AM Radio Transmitter Circuits for Beginners: A Step-by-Step Guide

AM Radio Transmitter Circuits for Beginners: A Step-by-Step Guide

Building an AM radio transmitter is an exciting project for electronics enthusiasts, especially beginners eager to explore radio frequency (RF) circuits. Amplitude Modulation (AM) transmitters are ideal for learning due to their simplicity and accessible components. In this SEO-optimized article, we’ll dive into beginner-friendly AM transmitter circuits from the vu3dxr.in blog, with direct links to their detailed schematics. We’ll also include external resources for authenticity and tips to boost your project’s success, all while driving backlinks to vu3dxr.in.

Why Build an AM Radio Transmitter?

AM transmitters modulate the amplitude of a carrier wave to transmit audio, operating in the medium wave band (500kHz–1600kHz). They’re simpler than FM circuits, making them perfect for hands-on learning about oscillators, modulation, and RF design. With circuits from vu3dxr.in, you can broadcast audio to a nearby AM radio and gain practical electronics experience.

Note: Transmitting without a license is illegal in most countries. Always check local regulations, such as FCC Part 15 rules, before testing. These circuits are for educational purposes.

Key Components of an AM Transmitter

A basic AM transmitter includes:

• Audio Amplifier: Boosts the audio input (e.g., from a microphone).
• RF Oscillator: Generates the carrier wave.
• Modulator: Combines audio with the carrier.
• Tank Circuit: Tunes the frequency using an inductor (L) and capacitor (C).
• Antenna: Radiates the signal.

You can source components like transistors (e.g., 2N3904) and capacitors from suppliers like DigiKey or salvage them from old radios, as suggested on vu3dxr.in’s Homebrew RF Circuits page.

Beginner-Friendly AM Transmitter Circuit from vu3dxr.in

The Series Modulated AM Transmitter from vu3dxr.in is a fantastic starting point for beginners. This low-power, crystal-controlled circuit is perfect for QRP (low-power) projects and uses minimal components.

Circuit Overview

• Crystal Oscillator: Ensures stable frequency output (e.g., 1000kHz).
• Transistor Q5: Modulates the carrier by varying the power supply.
• Potentiometer VR1 (10k): Adjusts Q5’s collector voltage to 6.6V.
• Tank Circuit (L1, C1): Tunes the signal to the desired frequency.

Link: Series Modulated AM Transmitter on vu3dxr.in

How It Works

1. The crystal oscillator generates a stable carrier wave.
2. Audio input (e.g., from a microphone) modulates the power supply via Q5.
3. The tank circuit filters the signal to the AM band.
4. A 10-foot wire antenna radiates the signal, receivable on a nearby AM radio.

Building Tips

• Use a crystal matching your target frequency (e.g., 1000kHz).
• Adjust VR1 for clear audio output.
• Match the antenna impedance with L2 and C2, as detailed in vu3dxr.in’s guide.

A Simpler Alternative: Poor-Man’s Transmitter

For an even easier build, try the Poor-Man’s Transmitter from vu3dxr.in. This circuit is ideal for creating a simple AM radio beacon using vintage components.

Circuit Highlights

• Oscillator: A single 2N3904 transistor generates the carrier.
• Modulation: A condenser microphone provides audio input.
• Tank Circuit: A variable capacitor (300–500pF) and inductor allow manual tuning.
• Power: Runs on a 9V battery.

Link: Poor-Man’s Transmitter on vu3dxr.in

Construction Steps

1. Build the oscillator with a 2N3904 and LC tank circuit.
2. Connect a condenser microphone for modulation.
3. Power with a 9V battery and attach a 3–10-foot antenna.
4. Tune the variable capacitor to your desired AM frequency.

Why It’s Great for Beginners

• Minimal components simplify assembly.
• Manual tuning teaches tank circuit fundamentals.
• Portable and low-cost, using salvaged parts.

Learn More: Homebrew RF Circuits on vu3dxr.in for component sourcing tips.

Common Beginner Questions

How Do I Tune the Frequency?

The Poor-Man’s Transmitter uses a variable capacitor for manual tuning. For fixed frequencies, the Series Modulated AM Transmitter relies on a crystal.

Can I Increase the Range?

Optimize the antenna and impedance matching, as explained in vu3dxr.in’s Homebrew RF Circuits. A 10–15-foot wire antenna can extend range within legal limits.

What If I Want a Beacon Without Audio?

Remove the microphone from either circuit. For the Series Modulated AM Transmitter, adjust VR1 for a steady carrier signal.

Where to Get Components?

Salvage from old radios or buy from Mouser Electronics. Vu3dxr.in’s Homebrew RF Circuits suggests local markets for vintage parts.

Safety and Legal Notes

• Low Power: Stay within legal limits (e.g., FCC Part 15).
• Licensing: Obtain a ham radio license for legal operation. Visit ARRL for details.
• Interference: Use proper filtering, as outlined in the Series Modulated AM Transmitter.

Why vu3dxr.in Is Your Go-To Resource

The vu3dxr.in blog offers:

• Detailed schematics for the Series Modulated AM Transmitter and Poor-Man’s Transmitter.
• Practical advice on QRP and DIY RF projects.
• Tips for troubleshooting and component sourcing via Homebrew RF Circuits.

Conclusion

Building an AM radio transmitter is a rewarding way to learn RF electronics. The Series Modulated AM Transmitter and Poor-Man’s Transmitter from vu3dxr.in are perfect for beginners. With minimal components and clear instructions, you can broadcast audio to a nearby AM radio. Explore more DIY RF projects at vu3dxr.in’s Homebrew RF Circuits and check Circuit Basics for additional tutorials. Always follow local regulations to enjoy this hobby safely.

Wireless Home theater Circuit using Bluetooth Headset

The post discusses a 200 + 200 watt wireless home theater circuit using a class D amplifier and a Bluetooth headset as the wireless module. The idea was requested by Mr. Sudipta Mandal.

The Request

I want to make my home theater wireless. My home theater model is Sony SRS-D9 2.1 channel. I also want the audio to be stereo. Range should me minimum 2 meters. Is it possible through Bluetooth module or RF transmitter & receiver? If so please suggest how to connect these modules to transmit and receive audio signals. If it is possible through Bluetooth then how to connect the Bluetooth module to my home theater? If a small circuit is required I can make it on my own but for that I need the circuit diagram and specifications of components required.

The Design

In one of the previous articles we learned regarding the internal constituents of a Bluetooth headset gadget and in another post we discussed how its speaker pins could be used for activating a relay.

In response to the above request, in this article we investigate how a Bluetooth Headset could be used for making a home theater system circuit.

The idea is simple, it's about finding a suitable differential power amplifier circuit  and integrating the Bluetooth Headset speaker wires with the inputs of the amplifier.

For the proposed application here we have used an example 200 + 200 watt class D power amplifier circuit using the IC TDA8953 from NXP Semiconductors.

The complete schematic of the power amplifier can be witnessed in the below given diagram. It includes two differential inputs meaning the chip supports a stereo class D input.

The output is single ended though and is capable of driving two ground referenced 4 ohm speakers rated at 200+ watts each.

Each of the inputs of the above shown class D amplifier could be directly configured with the cut/stripped speaker wires of a scavenged Bluetooth headset circuit as given below:

Disconnect the speaker wires from the speaker, strips the ends carefully for the recommended integrations with the amplifier inputs

For using both the inputs of the amplifier and for enjoying a stereophonic home theater response, another compatible and appropriately paired Bluetooth headset unit will be required. 

Once the integration of the two Headsets, paired with source Bluetooth is done, a throbbing crystal clear class D 400 watt stereo music could be experienced over the attached speakers.

The system could be positioned as a home theater system or simply for enjoying a pure 400 watts of music from your cell phone or other Bluetooth compatible gadgets.

If you already have a ready made home theater amplifier system, connect the input of the amplifier with any one cut/stripped speaker wire of the Bluetooth headset (if the amplifier is not a differential type) and make sure the negative line of the headset is made common with the amplifier negative line.

Alternatively a bridge network could be employed for rectifying the differential output from the headset speaker and the output could be directly joined with the inputs of the single ended amplifier.

Modifying a Bluetooth Headset Device for Personalized Applications

In the previous post we learned regarding the internal circuitry of a typical Bluetooth headset, in this post we'll see how the gadget can be modified or "hacked" in order to make it work for other personalized applications.

In the previous article we learned how to break open a Bluetooth headset device and also investigated the various components enclosed within.

Although most of the stages inside the headset appear to be too sophisticated to digest, the two elements which are still quite traditional are: the speaker and the mic, and those are exactly what we are interested in for implementing the proposed hacking procedures, because these two ports basically become the input and the output terminals of the device.

To be precise it's the speaker outputs that is more useful, which could be assumed to be generating analogue audio frequencies in a push-pull format. This analogue signal can be easily translated and converted into a logical signal for operating a toggling device such as a relay.

In the following couple of images we are able to see the speaker wires which could be simply cut and striped at the ends for accessing the processed analogue frequencies for the required modifications.

Once the above operations are made, it's all about integrating the wires with a bridge network followed by an opto coupler stage, as shown below:

The bridge network converts the differential output response from the Bluetooth speaker outputs into a full wave DC, which is further filtered by the 100uF capacitor to produce a clean DC across the opto input.

The DC is converted into a logical content across the collector/ground of the opto transistor. This output may be configured with any standard flip flop circuit for toggling any desired load.

The above toggling could be initiated by activating the Bluetooth headset with a data from a cell phone or any similar compatible device. Each time the speaker responds, the info gets translated into the above discussed toggling effect over a connected relay.

A flip flop circuit can be seen in the following figure which could be integrated with the above opto output for obtaining the intended relay operations.

Parts List

R3 = 10K,
R4, R5 = 2M2,
R6, R7 = 39K,
R4, R5 = 0.22, DISC,
C6 = 100µF/25V,
D4, D5 = 1N4148,
T1 = BC 547,
IC = 4093,


The above method explains an easy way of hacking a Bluetooth headset for remotely operating a particular appliance, in the next post (yet to be published) we'll learn how to hack a Bluetooth Headset as a wireless home theater system.

What's Inside a Bluetooth Headset

In this post we will learn what's inside a Bluetooth headset gadget and also know how to hack it for using it for other useful personalized applications.

The world is going digital at a rapid pace and advanced concepts such as Bluetooth are quickly replacing the other traditional form of technologies.

What's Bluetooth? It's another wireless transmission technology used for exchanging a wide variety of data in a precoded form over short distances via devices that may be compatible to cell phone, smart phones, laptops, PCs, Wi-Fi systems etc.

Basically Bluetooth also incorporates Rf waves but in a digitally coded form, quite unlike to the traditional FM or AM concepts.

It's an advanced and enhanced form of wireless technology that is designed to be able to connect with many compatible devices at a time without encountering synchronization problems or hurdles.

A Bluetooth headset is another related device which is designed to exchange (transmit and receive) data using Bluetooth technology across similar above mentioned compatible devices.

It's a very interesting RF device which could be hacked by an hobbyist in order to make it work for any desired customized application. For example we can use the headset device to make our home theaters systems completely wireless with crystal clear responses, or may be we can use it for controlling a few of the appliances across the rooms in our house or apartment.

Opening a Bluetooth Headset gadget

In order to experiment with a Bluetooth Headset you could probably buy a typical type that's shown below or if you already have one you can use it for the discussed hacking procedures.

To break it open you can use a screw driver as shown in the picture below. However you will need to maintain extreme dexterity and care while operating the gadget making sure you don't damage the internal circuitry.

Once the cover is removed, you would come across another plastic shielding which you can identically remove using the tip of your screw driver.

Once the inner protection shield is peeled of, the actual PCB with various components would pop out from the shell as shown below.

 In this position the few important things that would become visible are: two wires running toward a small speaker, two wires towards an in built MIC, an USB connector and an attached battery. See below for the details

For getting the entire assembly out of the box, you could probably go ahead and remove the speaker and the Mic from their respective locations, in order to study them in-depth.

The MIC could be found hidden inside a metallic clipping which could be pulled out with some careful effort.

Once removed.... the MIC, the speaker and the PCB with all the associated components could be studied in details as shown in the following figure:

Another important area we would be interested within the circuit is the USB socket, since its the input which receives all the data, and also the battery for getting well versed regarding what's inside a typical Bluetooth headset.

The battery is a 3.7V Li-ion, 120mAH battery, as may be witnessed in the following image:

OK that's it, now we exactly know all that's inside a Bluetooth headset gear, and it's time to learn a few of the simple hacking techniques that would enable us to use any Bluetooth headset unit for performing the intended operations.

The next post will explain how to hack a Bluetooth Headset for other personalized implementations such as for remotely operating an appliance, as a spy bug, and audio related applications such as for making wireless speaker systems and home theater systems.

5kva Ferrite Core Inverter Circuit

In this post we discuss the construction of a 5000 watt inverter circuit which incorporates a ferrite core transformer and therefore is hugely compact than the conventional iron core counterparts.

Written and Submitted By: Dhrubajyoti Biswas

First you need to find 60V DC power supply for powering the proposed 5kVA inverter circuit. The intention is to design a switching inverter which will enable change the DC voltage of 60V to a higher 220V at a lowered current. The topology followed in this scenario is the push-pull topology which uses transformer on the ration of 5:36. For voltage regulation, which you may need and the current limit – they are powered by an input voltage source. Also at the same rate, the inverter expedites the current allowed. When it comes to an input source of 40A it is possible to get 2 – 5A. However, the peak output voltage of this 5kva inverter is around 220V.

In regard to the architecture, Tr1 transformer has 5+5 primary turns and 18 for secondary. For switching, it is possible to use 4+4 MOSFET (IXFH50N20 type (50A, 200V, 45mR, Cg = 4400pF). You are also free to use MOSFET of any voltage with Uds 200V (150V) along with least conductive resistance. The gate resistance used and its efficiency in speed and capacity must be excellent.

 The Tr1 ferrite section is constructed around 15x15 mm. The L1 inductor is designed using five iron powder rings that may be wound as wires. For inductor core and other associated parts, you can always get it from old inverters (56v/5V) and within their snubber stages.

For integrated circuit the IC IR2153 can be deployed. The outputs of the ICs could be seen buffered with BJT stages. Moreover, due to the large gate capacitance involved it is important to use the buffers in the form of power amplifier complementary pairs, a couple of of BD139 and BD140 NPN / PNP transistors do the job well.

You may also try to use other control circuits like SG3525. Also, you can alter the voltage of the input and work in direct connection with the mains for testing purpose. The topology used in this circuit has the facility of galvanic isolation and operating frequency is around 40 kHz. In case if you have planned to use the inverter for a small operation, you don’t cooling, but for longer operation be sure to add a cooling agent using fans or large heatsinks. Most of the power is lost at the output diodes and the Schottky voltage goes low around 0.5V.

The input 60V could be acquired by putting 5 nos of 12Vbatteries in series, the AH rating of each battery must be rated at 100 AH

How to Wind the Ferrite Transformer TR1

The transformer TR1 is the main device which is responsible for stepping up the voltage to 220V at 5kva, being ferrite cored based it's constructed over a couple of ferrite EE cores as detailed below:

Since the power involved is massive at around 5kvs, the E cores needs to be formidable in size.

Remember you may have to incorporate more than 1 E core, may be 2 or 3 E-cores together, placed side by side for accomplishing the massive 5KVA power output from the assembly.

Use the largest one that may be available and wind the 5+5 turns using 10 numbers of 20 SWG super enameled copper wire, in parallel.

After 5 turns, stop the primary winding insulate the layer with an insulating tape and begin the secondary 18 turns over this 5 primary turns. Use 5 strands of 25 SWG super enameled copper in parallel for winding the secondary turns.

Once the 18 turns are complete, terminate it across the output leads of the bobbin, insulate with tape and wind the remaining 5 primary turns over it to complete the ferrite cored TR1 construction. Don't forget to join the end of the first 5 turns with the start of the top 5 turn primary winding.


E-Core Assembly Method

The following diagram gives an idea regarding how more than 1 E-core may be used for implementing the above discussed 5 KVA ferrite inverter transformer design:

Playing a Melody Using the Tone() function in Arduino

In this Arduino tutorial we’ll learn how to execute the tone() command for producing musical notes. The configuration will play a tiny musical tone that could be familiar to you.

Required Hardware for the Project

Arduino Board

Loud speaker – 8 Ohm 1 inch

Resistor – 100 ohms

Hook-up wires

Procedure:

It’s rather too straightforward and requires one of the speaker wires to be integrated with  pin8 via the 100 ohm resistor, and the other wire to the ground or the negative rail of the supply, as indicated the following schematic:

Image Courtesy: http://arduino.cc/en/Tutorial/Tone

The Programming Code

You will see an additional file (pitches.h) being included in the code. The file is preprogrammed with the tone pitch values of a few standard musical tunes.

To be more precise, you could find NOTE_C4 is middle C. NOTE_FS4 is F sharp and in the like manner. The programme of the following attached note table was originally formulated by Brett Hagman, according to which the tone() command was formed. The data becomes handy whenever an application demands the production of a musical note within an Arduino configuration.

The fundamental sketch may be learned as given under:

/*
  Melody
 
 Plays a melody
 
 circuit:
 * 8-ohm speaker on digital pin 8
 
 created 21 Jan 2010
 modified 30 Aug 2011
 by Tom Igoe
This example code is in the public domain.
 
 http://arduino.cc/en/Tutorial/Tone
 
 */
 #include "pitches.h"
// notes in the melody:int melody[] ={
  NOTE_C4, NOTE_G3,NOTE_G3, NOTE_A3, NOTE_G3,0, NOTE_B3,NOTE_C4};
// note durations: 4 = quarter note, 8 = eighth note, etc.:int noteDurations[] = {
  4, 8, 8, 4,4,4,4,4 };
void setup(){
  // iterate over the notes of the melody:
  for (intthisNote = 0;thisNote < 8;thisNote++) {
    // to calculate the note duration, take one second
    // divided by the note type.
    //e.g. quarter note = 1000 / 4, eighth note = 1000/8, etc.
    int noteDuration = 1000/noteDurations[thisNote];
    tone(8, melody[thisNote],noteDuration);
    // to distinguish the notes, set a minimum time between them.
    // the note's duration + 30% seems to work well:
    int pauseBetweenNotes =noteDuration * 1.30;
    delay(pauseBetweenNotes);
    // stop the tone playing:
    noTone(8);
  }}
void loop(){
  // no need to repeat the melody.

In order to create the pitches.h file you’ll need to click on the “new Tab” button which may look like this: →    

And simply paste the following code in it:

/*************************************************
 * Public Constants
 *************************************************/

#define NOTE_B0  31
#define NOTE_C1  33
#define NOTE_CS1 35
#define NOTE_D1  37
#define NOTE_DS1 39
#define NOTE_E1  41
#define NOTE_F1  44
#define NOTE_FS1 46
#define NOTE_G1  49
#define NOTE_GS1 52
#define NOTE_A1  55
#define NOTE_AS1 58
#define NOTE_B1  62
#define NOTE_C2  65
#define NOTE_CS2 69
#define NOTE_D2  73
#define NOTE_DS2 78
#define NOTE_E2  82
#define NOTE_F2  87
#define NOTE_FS2 93
#define NOTE_G2  98
#define NOTE_GS2 104
#define NOTE_A2  110
#define NOTE_AS2 117
#define NOTE_B2  123
#define NOTE_C3  131
#define NOTE_CS3 139
#define NOTE_D3  147
#define NOTE_DS3 156
#define NOTE_E3  165
#define NOTE_F3  175
#define NOTE_FS3 185
#define NOTE_G3  196
#define NOTE_GS3 208
#define NOTE_A3  220
#define NOTE_AS3 233
#define NOTE_B3  247
#define NOTE_C4  262
#define NOTE_CS4 277
#define NOTE_D4  294
#define NOTE_DS4 311
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_FS4 370
#define NOTE_G4  392
#define NOTE_GS4 415
#define NOTE_A4  440
#define NOTE_AS4 466
#define NOTE_B4  494
#define NOTE_C5  523
#define NOTE_CS5 554
#define NOTE_D5  587
#define NOTE_DS5 622
#define NOTE_E5  659
#define NOTE_F5  698
#define NOTE_FS5 740
#define NOTE_G5  784
#define NOTE_GS5 831
#define NOTE_A5  880
#define NOTE_AS5 932
#define NOTE_B5  988
#define NOTE_C6  1047
#define NOTE_CS6 1109
#define NOTE_D6  1175
#define NOTE_DS6 1245
#define NOTE_E6  1319
#define NOTE_F6  1397
#define NOTE_FS6 1480
#define NOTE_G6  1568
#define NOTE_GS6 1661
#define NOTE_A6  1760
#define NOTE_AS6 1865
#define NOTE_B6  1976
#define NOTE_C7  2093
#define NOTE_CS7 2217
#define NOTE_D7  2349
#define NOTE_DS7 2489
#define NOTE_E7  2637
#define NOTE_F7  2794
#define NOTE_FS7 2960
#define NOTE_G7  3136
#define NOTE_GS7 3322
#define NOTE_A7  3520
#define NOTE_AS7 3729
#define NOTE_B7  3951
#define NOTE_C8  4186
#define NOTE_CS8 4435
#define NOTE_D8  4699
#define NOTE_DS8 4978

Making a Wireless Doorbell Circuit

Today the traditional wired type of doorbells are gradually getting obsolete and are being replaced by the advanced wireless type of doorbells that are easier to install due to their hassle free set-ups. A simple wireless doorbell circuit is discussed in the following post which can be constructed at home.

Written and Submitted By: Mantra

303MHz TRANSMITTER with 32kHz Crystal

The initial circuit we are going to explore has a 32kHz crystal to crank out a tone which means that the receiver is unable to false-trigger.
We could perhaps experience a fault with the commercial RX-3 circuits every 2 minutes, this might be due to the chip detecting a frequency of 1kHz or 250Hz from the environment disturbance received by the RF transistor, to turn on an output.

That's exactly why the RX-3 receiver chip is untrustworthy. A 32kHz is a much better frequency to identify because it does not get rattled from environment resonance.
The functionality of a 303MHz circuit has been covered in this project WIRELESS DOORBELL.
We are not going over how the circuit works but explain the importance of some of the components and how they effect the range.
The Wireless Doorbell transmitter and receiver circuit are incorporated below:

All Transistors are 2N3563, the U shape coil is a single half turn using a 1mm copper wire with 5mm diameter

The most fundamental constituent is the transistor.
An excellent transistor is critical in the RF phase and the Japanese transistors are undoubtedly suits this objective.
The transistor employed in the 303MHz oscillator possesses an optimum frequency for the functionality of 1,000MHz in this most assuredly is where the gain is equal to "1," therefore we would like a transistor to have a unique gain at 300MHz.
A BC 547 transistor is not going to function at this frequency as a result now we have considered a good choice a 2N 3563 that may be inexpensive which enables it to work with up to 1,000MHz.  requirement papers when dealing with these transistors:


303MHz TRANSMITTER using 4049 IC

The following circuit works by using a CD 4049 IC to churn out the 32kHz frequency and four gates in parallel to transform the oscillator transistor on and off at the tone-rate.
An individual gate will not likely possess as much as necessary performance to suck the emitter to ground, nevertheless 4 gates will certainly bring along the emitter in close proximity to 0v rail. It ought not be at specifically 0v as the 6p would not possess a direct impact in sustaining oscillation.
The IC bears 6 gates just in case an input is probably above mid rail, the output moves LOW. Any time the input amounts to slightly below middle of the rail the output scales HIGH. The space between detecting a low and a high might not be massive as well as the gate will certainly pick up receptions referred to as "analogue signals."
However to obtain the oscillator circuit to startup, a resistor is positioned between output and input.
This will likely generate an oscillation at the maximum frequency for the gate roughly 500kHz to 2MHz..

All Transistors are 2N3563, the U shape coil is a single half turn using a 1mm copper wire with 5mm diameter

In case an additional gate is included along with a crystal hooked up between the output as well as the input, a "fight" transpires between the transmission coming from the 1M and the rate of recurrence transferred by the crystal. Considering that the crystal possesses a reduced impedance as compared to the 1M, it accomplishes a more substantial signal to input pin 11 along with the 2 gates function at the frequency of the crystal.
The precise characteristics of the correct way the reception from the crystal overtakes the signal administered back from the 1M resistor is not critical in spite of this providing you can contemplate the first gate starts out to rise in frequency from nil, every time the signal reaches 32kHz, it commences to initialize the crystal which in turn forces the signal on the reverse side and into the input pin of the first gate.

Each transmitters churn out the identical outcomes, a 303MHz carrier with a 32kHz modulation (frequency - despite the fact that we are unable to perceive sound in this frequency). Each possess the matching spectrum.

The oscillator coil is furthermore the radiator of the signal as well as the 1.5uH inductor on the "centre tap" of the coil is often as high as 10uH or as little as 1.5uH, with minimal variance in output.
The frequency might well need to be realigned somewhat if the inductor is modified.
We transformed it for a forty turn air-would coil working with.25mm wire on a 2mm former. This amplified the distance by one metre.
A sixty turn coil enhanced the range an additional 3 metres once it was subsequently expanded it added to the impact of the antenna. The pair of photos below exhibit the positioning of the air-inductors.

40 turn coil swapping the 1.5uH inductor. Sixty turn coil expanded to multiply the range of the wireless transmitter

All Transistors are 2N3563, the antenna coil is 2.5 turns of 1mm copper wire over a 5mm variable slug assembly

303MHz RECEIVER


This doorbell is cheaper than $8.00 therefore it is impossible to get the components independently for lower than that.
This sort of circuit formulates an excellent groundwork for exhaustive study. It is possible to investigate the RF side of the circuit not to mention the high impedance segments. Each gate includes promoting an extremely high gain and by applying a 1M from output to input the gate is saved in a state of stimulation, oscillating at approx 500kHz, in the event hardly any other parts encompass the gate to manage the frequency. This could be formulated to retain the gate dynamic to ensure that the tiniest signal is going to be processed.
When it comes to the gate between pins 13 and 12, the 1n capacitor between the input and ground lessens the frequency significantly, in addition to the impact of the 2n2 as well as 5k6 resistor.
The 2nd and 3rd gates straightforwardly improve the amplitude of the signal and never render any specific version of elimination of undesired receptions.
The consequence is an entire amplitude signal at the left-side of the crystal together with all varieties hash and backdrop disturbance, then again aside from the signal features a 32kHz factor, it is going to not commence to oscillate and the right side would have no reception. The crystal is the element that does nearly all of the "detection work" as well as inhibits misleading activating because it magically instincts out the 32kHz signal from the "hash" and produces an extremely unpolluted transmission to the transistor for in depth amplification.
This reception is heightened in conjunction with full rail as well as charges an electrolytic to actuate an audio chip.

Adjustable 0-100V 50 Amp SMPS Circuit

The high power adjustable switching power supply is perfect for the purpose of laboratory work. The topology used to design the system is switching topology – half controlled bridge.


Written and Submitted by: Dhrubajyoti Biswas

The switching supply is powered with IGBT transmitters and is further controlled by UC3845 circuit. The mains voltage goes straight through the EMC filter which is further checked and filtered on C4 capacitor.

As the capacity is high (50 amps), the inflow in the limiting circuit with Re1 switch and also on R2.

The relay coil and fan, taken from AT or ATX power supply is powered from 12V. The power is obtained via the resistor from 17V auxiliary supply.

It is ideal to select R1 so that the voltage at the fan and the relay coil limits to 12V. The auxiliary supply on the other hand uses TNY267 circuit and R27 facilitates protection from under-voltage of auxiliary power.

The power will not turn on if the current is less than 230V. The UC3845 control circuit results to 47% duty cycle (Max.) with the output frequency of 50 kHz. The circuit is further powered with the help of the zener diode, which actually helps to reduce the supply voltage and even helps to shift the UVLO threshold of lower 7.9V and upper 8.5V to 13.5V and 14.1V respectively.

The source initiates the power and starts working on 14.1V. It never goes below 13.5V and further helps to protect IGBT from desaturation. However, the original threshold of UC3845 should to set as low as possible.

The MOSFET T2 circuit controls, which helps to make Tr2 transformer work offers floating drive and galvanic isolation for the upper IGBT. It is through the forming circuits of T3 and T4 that it helps to drive T5 and T6 of IGBT and the switch further rectifies line voltage to Tr1 power transformer.

As the output is rectified and reaches an average, it is smoothed by L1 coil and C17 capacitors. The voltage feedback is further connected from output to the pin 2 and IO1. Furthermore, you can also set the output voltage of power supply with P1 potentiometer. There is no need for galvanic isolation of feedback.

It is because the control circuit is connected with the secondary SMPS and leaves no connection with the network. The current feedback is passed through the current transformer TR3 right onto 3 pin IO1 and the overcurrent protection threshold can be set using P2.

12V input supply may be acquired from an ATX power supply

+U1 and -U1 may be derived from mains 220V input after appropriate rectification and filtration

Also, please remember to place diodes D5, D5 ', D6, D6', D7, D7 ', transistors T5 and T6 on heat sink along with the bridge. Care should be taken to place snubbers R22 + D8 + C14, capacitors C15 and diodes D7 close to IGBT. The LED1 signals the operation of the supply and LED2 signals the error or the current mode.

The LED glows when the supply has ceased to work in voltage mode. When in voltage mode, the IO1 pin 1 is set to 2.5V else it usually has6V. LED light is an option and you may exclude the same during making.

Inductance: For power transformer TR1, the transformation ratio is around 3:2 and 4:3 in primary and secondary. There is also air gap in the ferrite core which is EE shaped. If you are looking for to wind all by yourself, use a core as it is in an inverter which should size around 6.4 cm2.

The primary is of 20 turns with 20 wires with each having diameter measuring 0.5mm to 0.6mm. The secondary 14 turns with 28 diameters is also of the same measurement like that of primary. Moreover, it is also possible to create windings of copper strips.

It is important to note that application of single thick wire is not a possible idea because of the skin effect. Now since the winding is not required, you may wind the primary one first followed by secondary. Tr2 forward gate driver transformer possesses three windings having 16 turns each. It is by using three twisted insulated bell wires that all windings has to be wounded at once leaving any air gap at the wound of the ferrite core.

Next, taking the main power supply from AT or ATX power supply unit of a computer with the core section of around 80 to 120mm2. The current Tr3 transformer is of 1 to 68 turn on ferrite ring and the number of turns or size is not critical here.

However, the process to orient the winding of transformers must be followed. Also you need to use double choke EMI filter. The output coil L1 has two parallel inductors of 54uH on iron powder rings. The total inductance is finally 27uH and the coils are wounded by two magnetic copper wires of 1.7mm in diameter, which makes the total L1 cross section to approx. 9 mm2.

The output coil L1 is attached to a negative branch which results no RF voltage in the cathode of diode. This facilitates mounting the same in heat sink without any insulation.

The max input power of the switched power supply is around 2600W and the resultant efficiency is above 90%. In switching power supply, you can use STGW30NC60W IGBT type or you can also use other variants like STGW30NC60WD, IRG4PC50U, IRG4PC50W or IRG4PC40W.

You can also use a fast output diode having adequate current rating. In the worst case scenario, the upper diode gets an average current of 20A while the lower diode in similar situation gets 40A. Thus it is better to use upper diode half-current than the lower one.

For upper diode, you can use, either HFA50PA60C, STTH6010W or DSEI60-06A else two DSEI30-06A and HFA25PB60. For lower or bottom diode you can use two HFA50PA60C, STTH6010W or DSEI60-06A else four DSEI30-06A and HFA25PB60.

It is important that the diode of the heat sink must lose 60W (approx.) and loss in IGBT may account to 50W. However, it is quite hard to ascertain the loss of D7 since it is dependent on Tr1 property.

Moreover, the bridge loss may account to 25W. The S1 switch enables shutdown in standby mode primarily because of the frequent mains switching may not be proper, specifically when using it for laboratory. In the standby state, the consumption is around 1W and S1 can be skipped.

If you are looking to construct a fixed voltage source of supply, it is also feasible but for the same it is better to apply transformer ratio of Tr1 for maximum efficiency, for instance, in the primary use 20 turns and in secondary use 1 turn for 3.5V – 4V.

Water Heater Buzzer Alarm Circuit

The post explains a simple water heater alarm circuit which may be used as a safety device for getting indications regarding the switched position of a water heater or a geyser through intermittent buzzer actuation. The idea was requested by Mr. Mathew.



The Request

Hi Friend,
To be frank i am new to your blog http://homemadecircuitsandschematics.blogspot.in
I was googling on how to make a reminder alarm for my water heater that i forget every time to switch off. I would be lot grateful if you could give me a circuit diagram through your website on how to make it. I am sure it would be beneficial for most of the people who gets into trouble with geyser switched on for long periods.
Looking for a piezzo buzzer circuit that sounds every one minute (adjustable) interval for a certain milliseconds or say one second (adjustable preferably again).
Hope your helping hand would guide me.
Regards Mathew Joy

The Design

The proposed water heater buzzer alarm circuit functioning can be studied by referring to the following discussion and the diagram:

A single IC 4093 which is a quad Schmidt NAND gate IC is used here for executing two operations simultaneously viz for generating the timing pulses and the for generating the buzzer frequency.

As may be witnessed in the given diagram, the design can be divided into three basic stages, where U1A forms the PWM timer pulse generator stage, U1B becomes responsible for creating the buzzer frequency while the remaining two gates are used as buffers for delivering the U1B frequency output to the transistor/piezo buzzer network.

When the heater is first switched ON, the circuit also actuates wherein C1 grounds the input of U1A rendering a high at its output which in turn keeps the U1B disabled from making the buzzer frequency.

With the above situation the buzzer stays silent for the moment until C1 charges via R1, D1, RV1 and via the high logic from the output pin3 of the IC. The delay period may be predetermined by suitably adjusting the duty cycle of the stage through RV1 (here it is intended to be 1 minute OFF and 2 sec ON)

A soon as this happens, a logic high appears at the input pin1/2 of the IC which instantly flips the output of U1A, enabling the U1B which now begins generating the required buzzer frequency, but only until C1 yet again discharges completely via R1, D2, RV1 and via the zero logic at pin3, the situation now reverts to the previous situation and continues repeating the procedures infinitely until the geyser is switched OFF.

This frequency is further buffered and transferred via U1D gates to the transistor buzzer driver stage which sounds the connected buzzer/coil assembly generating an ear piercing audible sound, indicating that the heater or the geyser is in the switched ON position and may be needs an attention.

SMPS Halogen Lamp Transformer Cicuit

One of the best substitutes for traditional light transformer for halogen bulbs is the electronic halogen transformer. It can also be used with non-halogen bulbs and any other form of resistive loads that does not run on RF current.

 Written and Submitted By: Dhrubajyoti Biswas

The electronic halogen lamp transformer works on the principle of switching power supply. It does not run on secondary rectifier like the switching power supply, for which DC voltage is not needed to run the same. Moreover, it doesn’t have the option of smoothing after network bridge and it is simply due to the absence of electrolyte the application of thermistor does not come in application. The design of the electronic halogen transformer also eliminates the issue with power factor. Designed with MOSFET as a half-bridge and IR2153 driving circuit, the circuit is equipped with upper MOSFET driver and also has its own RC oscillator. The transformer circuit runs on a frequency of 50 kHz and the voltage is around 107V at the primary pulse transformer, which is measured as per the following calculation mentioned below:

Uef = (Uvst-2) . 0,5 . √(t-2.deadtime)/t [Here Uvst is the input line voltage and the resulting dead-time in IR2153 is set to 1. The value 2us and t is stated as the period and especially in regard to 50 kHz.].

However, upon substituting the value with the formula: U = (230-2) . 0,5 . √(20-2.1,2)/20 = 106,9V, the voltage gets reduced by 2V at the diode bridge. It is further subdivided by 2 at the capacitive divider, which is made of 1u/250V capacitors, thus reducing the effective value at dead-time.

The Tr1 transformer on the other hand is a pulse transformer placed on ferrite core of either EE or E1 can be lent from SMPS [AT or ATX]. While designing the circuit, it is important to bear in mind that the core should maintain a cross section of 90 – 140mm2 (approx.). Furthermore, the number of turns also has to be adjusted with based upon the state of the bulb. When we try to determine the calculation of transformer rate, we usually take it for consideration that the primary rate is the effective voltage of 107V in case of 230V output line. The transformer derived from AT or ATX generally gives 40 turns on primary and is further sub-divided into two parts having 20 turns on each primary – one that lies under the secondary while the other above the same. In case if you are using 12V, I would recommend using 4 turns and the voltage should be 11.5V. For your note, the transformation ratio is calculated with a simple division method: 107V / 11.5 V = 9.304. Also in the secondary section, the value is 4t, so the primary value should be: 9.304 . 4t = 37t. However, since the bottom half of the primary remains in 20z, the best option would be wind the top layer by 37t - 20t = 17t. And if you can trace out the original number of turns in secondary, things will be far easier for you. If the secondary is set to 4 turns just unwind 3 turns from the top of the primary to derive the result. One of the simplest procedures for this experiment is using 24V bulb, albeit the secondary to choose should be 8-10 turns.

The IRF840 or STP9NK50Z MOSFET without the absence of heat sink can be applied to derive the output of 80 – 100V (approx.). The other option would be use STP9NC60FP, STP11NK50Z or STP10NK60Z MOSFET model. In case if you are looking to add more power, do use heat sink or MOSFET with higher power, such as 2SK2837, STB25NM50N-1, STP25NM50N, STW20NK50Z, STP15NK50ZFP, IRFP460LC or IRFP460. Be sure to consider that the voltage should be Uds 500 – 600V. Care should also be taken, not to have a long lead to the bulb. The main reason is, in case of high voltage it may result to drop of voltage and cause interference mainly due to inductance. One last point to consider you can’t measure the voltage with the help of multimeter.

SMPS Welding Inverter Circuit

If you are looking for an option to replace conventional welding transformer, the welding inverter is the best choice. Welding inverter is handy and runs on DC current. The current control is maintained through potentiometer.

 Written and Submitted By: Dhrubajyoti Biswas

When developing a welding inverter, I applied forward inverter with two switches topology. Here the input line voltage traverses through the EMI filter further smoothing with big capacity. However, as the switch-on current pulse tends to be high there needs the presence of softstart circuit. As the switching is ON and the primary filter capacitors charges via resistors, the power is further zeroed by turning the switching ON the relay. The moment the power is switched, the IGBT transistors gets used and are further applied through TR2 forward gate drive transformer followed by shaping the circuit with the help of BC327. The control circuit used in this scenario is UC3844, which is very much similar to UC3842 with pulse-width limit to 50% and working frequency to 42 kHz. The control circuit draws the power from an auxiliary supply of 17V. Due to high currents, the current feedback uses Tr3 transformer. The voltage of 4R7/2W sensing register is more or less equal to the current output. The output current can be further controlled by P1 potentiometer. Its function is to measure the feedback’s threshold point and the threshold voltage of pin 3 of UC3844 stands at 1V.

One important aspect of power semiconductor is that it needs cooling and most of the heat generated is pushed out in output diodes. The upper diode which consists of 2x DSEI60-06A should have the capacity to handle the current at an average of 50A and loss till 80W. The lower diode i.e. STTH200L06TV1 also should the average current of 100A and loss till 120W. On the other hand, the total max loss of the secondary rectifier is 140W. The L1 output choke is further connected with the negative rail. This is a good scenario since the heat sink is barred from hi-frequency voltage. Another option is to use FES16JT or MUR1560 diodes. However, it is important to consider that the max current flow of the lower diode is twice the current to that of the upper diode. As a matter of fact, calculating IGBT’s loss is a complex procedure since besides conductive losses switching loss is another factor too. Also each transistor loses around 50W. The rectifier bridge also loses power till 30W and it is placed on the same heat sink as IGBT along with UG5JT reset diode. There is also the option to replace UG5JT with FES16JT or MUR1560. The loss of power of the reset diodes is also dependent upon the way Tr1 is constructed, albeit the loss is lesser compared to the loss of power from IGBT. The rectifier bridge also accounts to power loss of around 30W. Furthermore when preparing the system it is important to remember to scale the maximum loading factor of the welding inverter. Based upon the measurement, you can then be ready to select the correct size of the winding gauge, heat sink etc. Another good option is to add a fan as this will keep a check on the heat.

The Tr1 switching transformer is wounded two ferrite EE core and they both have the central column section of 16x20mm. Therefore, the total cross section calculates to 16x40mm. Care should be taken to leave no air gap in the in the core area. A good option would be to use 20 turns primary winding by wounding it with 14 wires of 0.5mm diameter. The secondary winding on the other hand has six copper strip of 36x0.55mm. The forward drive transformer Tr2, which is designed on low stray inductance, follows trifillar winding procedure with three twisted insulated wire of 0.3 mm diameter and the windings of 14 turns. The core section is made of H22 with the middle column diameter of 16mm and leaving no gaps. The current transformer Tr3 is made of EMI suppression chokes. While the primary has only 1 turn, the secondary is wounded with 75 turns of 0.4 mm wire. One important issue is to keep the polarity of the windings. While L1 has ferrite EE core, the middle column has the cross section of 16x20mm having 11 turns of copper strip of 36x0.5mm. Furthermore, the total air gap and the magnetic circuit are set to 10mm and its inductance is 12uH cca.

The voltage feedback does not really hamper the welding, but it surely affects the consumption and the loss of heat when in idle mode. The use of voltage feedback is quite important because of high voltage of around 1000V. Moreover, the PWM controller is operating at max duty cycle, which increases the power consumption rate and also the heating components.

The 310V DC could be extracted from the grid mains 220V after rectification via a bridge network and filtration through a couple of 10uF/400V electrolytic caapcitors.

The 12V supply could be obtained from a ready-made 12V adapter unit or built at home with the help of the info provided here:

Variable LED Intensity Controller Circuit

The post presents a couple of simple LED intensity controller circuit which may be appropriately configured for specific related applications. The idea was requested by Mr. Chand.

The Request

Hello Swagatam

I would like to have a circuit designed by you which is very simple and straightforward. This will be incorporated as a stand alone feature in a device which I am working on. What my requirements are -

1. A row of 12 displays (1 seven segment type x 12)

2. A potentiometer with knob to control each display illumination individually ( so in all 12 pot knobs). Each knob increases or decreases the intensity value from 0 to 9 for its individual display.

3. A separate row of 3 displays (1 seven segment type x 3). Function remains the same as point number 2 above.

Please let me know the cost for this circuit along with the schematics.

Thanks

Chand Sharma


The Design

The proposed LED intensity controller circuit may be learned as shown in the diagram.

Two diagrams can be seen, the left hand side may be used for controlling common anode type displays while the right hand side for common cathode types.

The design is basically a common collector BJT circuit where the base potential of the relevant transistors get proportionately delivered across their emitter base terminals.

Thus by varying the potential at their bases the emitter potential is also proportionately varied with a range right from 0V to the maximum supply voltage level (-0.7V).

Each of the following LED intensity controller modules could be used for the proposed 7 segment LED display control application. The preset may be replaced with a pot and its dial appropriately calibrated for getting the intended varying illumination through a range of 0 to 9.

Alarm Signal Generator IC ZSD100 Datasheet, Application Circuits

The ZSD100 is an alarm frequency generator IC which incorporates a frequency swept alarm signal generator designed solely for fixed and vehicle protection alarm systems.


For acquiring the specified alarm sound from this IC, just a single ZSD100, two timing capacitors, an in-expensive TO92 darlington, piezo transducer and coupling transformer is everything that becomes necessary to generate an extremely loud, ear piercing 120 dB warning siren.

Together with an acoustic frequency signal generator, low frequency sweep generator, shut down circuitry and output driver stages, the ZSD100 has been attributed with all functionality crucial to generating an approved alarm indication.

You may get this IC with a choice between an 8 pin DIL or SO bundle the IC grants an inexpensive stream-lined approach to siren signal technology. The system may be powered from inputs of 4V as much as 18V which specifically becomes suited for security detectors in battery driven products, burglar alarms and vehicle anti robbery techniques

FUNCTIONAL Information

The acoustic indication of the ZSD100 is created employing a squarewave oscillator whose operation is competent of directly triggering numerous output circuits. To generate a peculiar alarm siren sound, the frequency of the audio oscillator is swept over an allocated 2:1 spectrum by another, lower frequency oscillator. The frequencies of both the oscillators are regulated by R T (INT) and capacitors C MOD and C OUT

PIN DESCRIPTIONS

1. RT: Non-obligatory superficial resistor for enhanced frequency management. An peripheral resistor boosts the domination of each the modulating and output oscillators. The RT pin is furthermore employed to energize the gadget down. Possibly attaching RT to VCC or an open circuit would probably bring about the device getting crippled.

2. SAW: Choice of modulation waveform is done employing the SAW pin. An open circuit generates a triangle wave, sawtooth is accomplished by joining SAW to the CMOD pin.

3. CMOD: An exterior capacitor would be used to program the low frequency modulating oscillator. The worth of CMOD advisable is between 0.1μF and 10 0μF.

4. GND

5. COUT: An secondary capacitor would be used to program the output oscillator. The value of COUT endorsed is between 1nF and 100nF.

6. Q Non inverted output driver

7.Q Inverted output driver

8. VCC

Alarm Circuits Using ZSD100

Simple Greenhouse Temperature Regulator Circuit

The post discusses a simple electronic temperature regulator circuit which could be specifically used for regulating greenhouse temperatures. The idea ws requested by Mr. Leo.


The Request
 
I am looking for a guide to build a basic temp regulator circuit. I have a solar charger bought from lidl,(SLS 2200 A1) which has outputs for 5, 7.5 & 9.5v DC 0.5A. it will be used for soil heating in a greenhouse. 

My idea is to use black drip irrigation pipe as a 'solar panel' to heat the water and with a low volume pump regulate the temp under a propagation tray. Any advise is greatly appreciated. 

I have seen similar setups for egg incubators , fridge temp controls, etc. but need it at an allotment, so only power source is small panel. also if possible would it be possible to increase capacity of internal battery and have a heating element added. Thank once again. Leo


The Design


Before getting into the main circuit concept, it would be interesting to learn regarding a few of the parameters expressed in the above request, as given below:


What is "black" drip irrigation: We all probably have heard a lot about drip irrigation, a method in which water is fed to the crops across the entire allotted field through a network of narrow pipe lines wherein water is allowed to drip directly at the bottom of the stem of the crop for a sustained period of time. The method helps to save water and allows the water to reach the crucial areas such as the roots of the crop resulting in a better growth and efficiency.


Here an identical approach is implemented but the conventional pipes are replaced with black coiled PVC pipes. The back coiled pipe helps to absorb the heat from the sun rays naturally and allow the water passing through it to become warm naturally without depending on costly artificial utility electricity. The warm water ultimately helps to heat up the soil deep inside for acquiring the intended greenhouse effects.

What's a Propagation Tray: These could be arrays of plastic plantation pots arranged in a large tray like fashion for allowing deeper soil content to the seedlings over minimal spaces, it's specifically designed for optimizing indoor plantations.


Allotment: It may refer to a small garden or a plot of land as explained here:

http://en.wikipedia.org/wiki/Allotment_%28gardening%29

The Solar Panel: The specified solar panel is a self contained unit which includes a solar panel with outputs at 5, 7.5 & 9.5v DC (0.5A). It also includes a 4-step charge indicator circuit and most interestingly it includes a built-in 2200mAH Li-ion battery so that you don't have to bother about external battery integrations, rather would be able to use the existing facility under overcast conditions.

Now let's return to the actual requirement of the proposed greenhouse temperature regulator circuit, the idea here is to sustain a raised temperature of the soil by 10 to 20 degrees Celsius above the atmospheric temperature for boosting or enhancing seed germination. Because seeds normally germinate faster in soils that are warmer than the atmosphere, which in turn results in an initial stronger root development instead of bigger leaf development.

Generally, heat mats are used below the propagation trays for heating the soil but in the present application the drip water is itself heated and used for generating the same results, which looks much impressive, since heat mats could at times get messy causing sparks, fire or over heating of the soil (if the attached thermostat fails).

Nevertheless, the electronic temperature controller circuit discussed below could be used with any heating system, including heat mats.

In the proposed design, the natural heating of the water within the black pipes is aided by an external heating element until the temperature of the water reaches the optimal point. As soon as this threshold is sensed the heater is switched off by the regulator circuit and held at that position until the temperature falls back to a relatively cooler level.

D1 = 1N4148, A1---A3 = 3/4 LM324, Opto = 4n35

Referring to the diagram above which is actually a simple temperature controller circuit, could well be used for regulating the soil temperature in the proposed greenhouse application.

Here the temperature sensor D1 is our very own "garden" diode (no pun intended ) 1N4148 which translates every one degree (C) rise in the ambient temperature into a 2mV drop across itself.

The opamp A2 is specifically arranged to detect this change in voltage across D1 and feed the difference to A3 such that the result illuminates the LED inside the attached opto coupler IC.

The threshold at which the above action takes place could be preset with the help of P1.

The output of the opto is connected with a NPN driver stage which is responsible for switching off the heater as soon as the above threshold is reached.

The sensor and the heater may be placed across any desired position, as per the user preference. For example the heater could be positioned below the propagation tray, or inside the water tank from where the water is being supplied to the black pipes.

On same grounds the sensor may be placed anywhere around, could be below the propagation trays, inside the soil, inside the pipe or simply inside the water tank.

The capacity of the unit could be upgraded as per the application, simply by employing a heavier rated solar panel and by replacing the TIP122 with a higher rated mosfet. The heater may also be upgraded as per the requirements.

Dual A/C Relay Changeover Circuit for Power Saving and Efficiency

 The post explains a simple relay changeover circuit which may be used for switching a couple of A/Cs or any similar load alternately in order to avoid misuse and save power.

The Request

Here is the situation:

State: California.

Facility: Church.

The electric rate is greatly influenced by peak usage in any 10 or 15 minute period during the month. So if usage exceeds the threashold value once in the month, the rate for every KWH in the month goes way up.

Concern: We have 2 large airconditioning units. If both are run at the same time we will exceed the threashold power consumption, and trigger the high rate for the entire month. People keep turning on both units whenever they feel too warm with no regard for costs.

Need: A (24V) circuit that works with the A/C thermostats such that: A/C unit 1 turns of/on based on its own (programmable) thermostat; and A/C unit 2 only comes on if 2 conditions are met: a) unit 1 is not running, and b) the thermostat for unit 2 is calling for cooling.

Can you design a simple relay circuit that would disable unit 2 if/when unit 1 is running?

- Lyndon

Circuit Designed and Drawn by: Abu-Hafss

The Design

According to the request:

A/C unit2 ON/OFF switch should stay disabled while or as long as A/C1 is running and in a switched ON position.

The second condition may be ignored since the thermostat of A/C 2 would itself  keep the system switched OFF irrespective of A/C1 condition or the relevant ON/OFF switches.

The above circuit which was designed by one of the dedicated readers of this blog Mr. Abu-Hafss fits the situation perfectly and satisfies the requested need

As can be seen, the design consists of a simple relay circuit which enables toggling of A/C1 and A/C2 in an alternate fashion, and never allows both to be activated at the same time.

In the circuit we have a transformer based full bridge rectifier power supply circuit with a "changeover" relay configured with its output potential. The power supply input is hooked up with the A/C power switch such that the relay activates whenever A/C 1 is switched ON.

The relay assembly has its contacts wired up with A/C 2 in such a way that as long as the relay is deactivated, A/C2 is allowed to get the switch-ON power through the relay's N/C contacts. However the moment the relay toggles from its N/C contact to N/O, the power line for A/C2 is cut-off, fulfilling the intended purpose as discussed in the above sections.