Monday, June 30, 2014

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.

Input Trigger Synchronized Monostable Timer Circuit Using IC 555

Here we study a simple IC 555 based monostable circuit whose output monostable time duration starts only after the input trigger is released thus making sure that the trigger ON time duration is added with the monostable's pre-programmed ON time duration. The idea was requested by Mr. John Brogan

The Request


I would like to know if I could hire you for a very simple project. This is to help me learn circuits.

I am looking for the following type of circuit (see below). Could you let me know what it would cost to design?

There will be 4 pins on the circuit board. 2 pins on the left side of the board, 2 pins on the right.

When someone closes the circuit of the LEFT side of the board, either momentarily, or for however long they keep the circuit closed, the pins on the RIGHT side of the board close *PLUS* 2 minutes after the time the circuit on the LEFT side of the board is opened. (that’s the part I’m stuck on – how to make a circuit stay closed for “n” minutes past the time another circuit is opened.

Please let me know what you would charge to diagram this and list the parts I need to buy to make this.

Thank you!

John Brogan

The Design 
In other words, the above request demands a monostable whose output on state delay will initiate only once the input trigger is released, meaning suppose the monostable is designed to produce a delay of 2 minutes, and let's assume the input trigger hold time to be x minutes, the total delay at the output pin3 of the IC should be then = 2 minutes + "x" minutes.

The design may be simply configured by adding a PNP stage to a standard IC 555 monostable circuit.

Referring to the figure below we see a standard IC 555 monostable circuit which produces an output high for a time delay determined by R2 and C1. This initiates each time pin2 is grounded momentarily or may be for some relatively longer period of time.

However normally this would happen as soon as pin2 is grounded without considering the trigger ON duration, and we don't want this situation for the proposed design.

The issue is effectively remedied by the inclusion of the PNP device T1 across the shown position of the circuit.

As suggested in the request when the left pins are closed, T1 is allowed with a negative bias forcing it to conduct.

The above condition allows the output to go high but shorts the timing capacitor C1 via T1 emitter/cpllector so that it is unable to charge until the left pins are opened by the user.

Once the left pins are released, C1 is allowed to charge and initiate the monostable counting operation wherein the relay actuates and closes the right pins for a total duration of the set two minutes plus the duration for which the input was held closed.

Saturday, June 28, 2014

SMPS 2 x 50V 350W Circuit for Audio Power Amplifiers

This article will illustrate a simple procedure to devise an unregulated switching symmetric power supply of 350W. This unit can be substituted with the standard audio amplifier power supply to reduce expense and also the weight. The proposed power supply works as a half-bridge with no regulation.

Written and Submitted by: Dhrubajyoti Biswas

My power supply relies on two N MOSFET and run by IR2153 integrated circuit. The IR2153 is powered by a power resistor of 27K 6W. The ripple at full load is recorded below 2V. The use of Zener diode (15V) ensures voltage stabilization and the operating frequency is set to 50 kHz (approx.). At the point of the input, I have placed a thermistor to force a check on the peak current when the capacitor is getting charged.

This same phenomenon can be found in AT/ATX power supply unit of a computer. Moreover, to ensure low leakage inductance and full voltage output, the first half of the primary is wounded in 20 turns followed by the secondary wound. Also to assure safety in the system, do be sure to connect the output (center tap 0V) to the earth.

The chokes used in the design will facilitate removal of RF output ripple. The number of turns and the core which is found in PC supply is not a critical factor. Additionally, the 6k8 resistors at the output section is used to discharge capacitors after it is switched off and this way it helps to prevent the voltage increase during no load.

The proposed Switched power supply 2x 50V 350W operates in single switch forward topology. It has an operating frequency of 80-90 kHz and has IRF2153 control circuit which is very much similar to that of US3842. However, the duty cycle is lesser and is limited to 50%.

The Tr1 transformer was devised by rewinding the SMPS ATX transformer and its primary inductance is 6.4 mH (approx.). The core of the system has no air gap and the primary inductance is further broken in two parts: The first half is the wind and the second is the winding.

Moreover, it is also feasible to deploy the original primary bottom half without rewinding. This type of power supply aptly suits for power amplifier applications. If required it may be also safeguarded against overload or short circuit and the voltage of the output could be stabilized. The Feedback of the system may be enabled through the help of optocoupler.

It is important to note that in regard to 350W power, care should be taken that in the conductive state the typical resistance should not cross more than 0.8R. MOSFET can also be used to lower the point of resistance. Interestingly, the smaller the resistance better is with the system.

The voltage tolerance is in the range of 900-1000V. In the worst case scenario 800V can be used. Considering this, the best MOSFET I found was SPP17N80C3 or 900V IGBTs.

Coil Details:

The main transformer which can be seen integrated with the mosfets may be wound on a standard 90 by 140mm^2 ferrite bobbin core assembly.

The primary side winding consists of  40 turns of 0.6mm super enameled copper wire. Remember to stop after 20 turns, put an insulation layer with an insulation tape and wind the secondary winding, once the secondary is wound, insulate it again and continue with the remaining 20 turns over it. Meaning the secondary winding gets sandwiched between the primary 20 + 20 turns. The center tap of this 20+20 may be connected with the body of the SMPS for an improved stabilization and cleaner outputs in terms of ripples or buzzing interferences.

The secondary consists of a center tapped 14 x 2nos turns made by winding 0.6mm super enameled copper wire.

The input and output filter coils may be wound on ferrite torroidal cores. The paired winding must be wound on the same individual torroidal cores using 0.6mm super enameled copper wire with 25 turns on each arm of the relevant supply terminals.

DIY Taser Gun Circuit

A Taser also known as Stun Gun is one non-lethal electric shock producing unit used to paralyze a person for a time being without causing any severe damage or injury. It is a very useful device, especially to immobilize an attacker.

The use of stun gun is restricted in most of the countries. However, in the United States of America, some state allows use of stun gun.

A stun gun is available in variety of styles like lipstick stun guns, cellphone stun guns, stun batons, police force stun guns, pink ribbon stun guns and disguised stun guns.

How it works?

A Taser functions like two-stage voltage converter. In the first stage, the high frequency switching transformer increases the battery voltage to several kV to charge the capacitor. After the capacitor is charged, it powers the second transformer by increasing the voltage to 10 – 50kV (approx.) with the repetition rate of 5-40 Hz (approx.).

Taser Type
There are basic types of Taser: Multiplier, Thyristor and spark gap. Multiplier Taser is made of one transformer having voltage of higher output and it runs on DC voltage. This type of Taser also has high-voltage capacitors and diodes and it is for the capacitors that multiplier Taser makes loud sound. The Thyristor type is the most efficient one. Here the voltage of the capacitor is not high (250 – 500 V approx.) and it functions with the aid two main components: resistive divider (neon lamp) and diac. The spark gap guns on the other hand is the most cheapest and ineffective stun gun. As the name implies, it has spark gap to function and the voltage of the battery is charged with transistor converter.

How I made my Taser

Of the three types of Tasers, I chose to go ahead with the Thyristor because of its effectiveness. I used MOSFET (Metal–Oxide–Semiconductor Field-Effect Transistor) to build the voltage converter. The main reason to use MOSFET is purely from the point of efficiency. In a push-pull converter which is generally used in stun guns, the level reaches around 20% whereas in MOSFET the converter gives efficiency as much as 75% with the working frequency of 80-120 kHz. I then used a gate thyristor for the second switch along with four neon glow lamps with the ignition voltage of 95V and the pulse repetition rate of 30 – 50 Hz. For inverter transformer, I preferred to use EE core based transformer keeping the middle column cross-section of 20 – 25 mm2. The air gap of 0.5mm thickness is place in the mid column. The primary polarity is set to 2x12 turns of the diameter of the wire (0.4mm) while the secondary polarity is set to 700 turns of wire (0.1mm). The secondary polarity is wounded in multiple isolated layers. The reason to isolate the layers is to avoid breaking the wire enamel under high voltage. There are two electrodes in a Taser gun. They look like a dart and are connected to the main unit with a conductive wire.

One can power a stun gun with either six 1.5 V cells or seven 1.2 V cells. The best option is to have two cells or Li-pol or Li-ion connecting the series. It should be note that stun gun draws current of around 1.5 V for which the ordinary batteries would not work in the same.

Written and Submitted By: Dhrubajyoti Biswas 

Friday, June 27, 2014

6V Battery Charge Controller with Over Current Protections

In this post we learn regarding a simple 6V battery charge controller circuit, which could be used in conjunction with a solar panel, or an AC/DC adapter input. The circuit also includes a 4 stage battery status indication feature, an over current controller stage, automatic switch OFF for the load and battery charging, and also a separate cell phone charging outlet. The idea was requested by Mr. Bhushan Trivedi.

The Request

Dear Swagatam,

Thank you very much for your continued support.

I have a few minor changes to the design now, which I would like to request you for incorporating in the circuit design.  I would like to express that cost of the PCB and components is a big concern, but I do understand quality is also very important. Hence, I request you to strike a fine balance between the performance and cost of this circuit.

So to begin with, we have this BOX, in which will house the 6V 4.5 Ah SMF Lead Acid Battery and the PCB too.

The 6V 4.5 Ah Battery will be charged either through the following options from one single input:

 a) A 230 V AC to 9V DC Adaptor (I wish to go ahead with a 1 amp rating charger, your views?) ‘OR’

 b) A 3-5 Watt Solar module (Max Voltage: 9 V (6V nominal), Max Current: 0.4 to 0.5 Amps)

The battery can be charged by only one supply at a time hence will only have one input on the left side of the box. For the time when this battery is being charged, there will be small red led light which glows on the font face of the box (Battery Charging Indicator in diagram)

Now, at this point, the system should also have a battery level indicator (Battery level Indicator in diagram)

I wish to have three levels of indications for the battery state. These tables state the open circuit voltage. Now with the very little electronic knowledge I have, I am assuming this is ideal voltage and not the actual conditions, right? I think I will leave that on you to decide and use any correction factors if required for calculations.

I wish to have the following indicator levels:

Charge level 100% to 65% = Small Green LED is ON (Yellow and Red LED off)

Charge level 40% to 65% = Small Yellow LED is ON (Green and Red LED off)

Charge level 20% to 40% = Small Red LED is ON (Green and Yellow LED off)

At 20% Charge level, battery disconnects and stops supplying output power.

On the Output side now (Right Side View in diagram)

The system will supply power to the following applications:

a) 1 Watt, 6V DC LED Bulb – 3 No’s

b) One output for Mobile Phone Charging
I wish to incorporate a feature here. As you see, the DC loads connected to the battery are of relatively less wattage. (just a mobile phone and three 1 watt LED Bulbs). Now, the feature to be added in the circuit should kind of work as a fuse ( I don’t mean an actual fuse here). Assume if a CFL bulb is connected here or some other application of higher wattage rating, power supply should be cut off. If the total power drawn is in excess of 7.5 Watts DC connected to this system, the system should cut off supply and shall only resume when the load is below 7.5 Watts. I basically wish to ensure that this system is not misused or drawn excessive energy from, thereby damaging the battery. This is just an idea. I do however understand this can potentially increase the complexity and cost of the circuit. I will look for your recommendation on this on whether to include this feature or no as we already are cutting off the battery supply once the state of charge reaches 20%.

I hope you find this project exciting to work on. I look forward to receiving your much valued inputs on this.

I am thanking you for all your help till now and in advance for your extended cooperation on this.

Kind Regards,


The Design

Here's a brief explanation of the various stages included in the proposed 6V automatic battery charge controller circuit:

The left side LM317 is responsible for producing a fixed 7.6V charging voltage across its output pin and ground for the battery, which drops to around 7V via D3 to become an optimal level for the battery.
This voltage is determined by the associated 610 ohm resistor, this value can be reduced or increased for changing the output voltage proportionately if required.

The associated 1 ohm resistor and the BC547 restricts the charging current to around a safe 600mA for the battery.

The opamps A1---A4 are all identical and perform the function of voltage comparators.
As per the rules if the voltage at their pin3 exceeds the level at pin2, the corresponding outputs become high or at the supply level..... and vice versa.

The associated presets may be set for enabling the opamps to sense any desired level at their pin3 and make their corresponding outputs go high (as explained above), thus A1 preset is set such that its output becomes high at 5V (Charge level 20% to 40%)....A2 preset is set to respond with an output high at 5.5V (Charge level 40% to 65%), while A3 triggers with a high output at 6.5V (80%), and finally A4 alarms the owner with the blue LED at battery level reaching the 7.2V mark (100% charged).

At this point the input power will need to be switched off manually since you did not demand for an automatic action.

Once the input is switched off, the 6v battery level sustains the above positions for the opamps, while the output from A2 ensures that the TIP122 conducts keeping the relevant loads connected with the battery and operative.

The LM317 stage at the right is a current controller stage which has been rigged to restrict the output amp consumption to 1.2 amps or around 7 watts as per the requirements. The 0.75 ohm resistor may be varied for altering the restriction levels.
 The next 7805 IC stage is a separate inclusion which generates a suitable voltage/current level for charging standard cell phones.

Now, as power is consumed the battery level begins receding in the opposite direction, which are indicated by the relevant is the first one to shut off illuminating the green LEd, which shuts off off below 6.5V illuminating the yellow LEd which identically shuts off at 5.9V making sure that now the TIP122 no longer conducts and the loads are shut off....but here the condition may oscillate for some moment until the voltage finally reaches below 5.5V illuminating the white LEd and alarming the user for an input power switch on and commence the charging procedure.

LM317 IC Tester Circuit

Here is simple but handy testing circuit for LM317 adjustable voltage regulator IC. I am sure it can be used to test other similar ICs like LM117, LM158, LM358 etc.

The circuit is pretty straightforward. The circuit is based on normal configuration of adjustable voltage regulator.
For details follow

A DPDT switch is used to connect the ADJ pin of the IC to either ground or to the resistor R1. When connected to ground, the output should be at the lowest level around 1.2V and when connected to R1 the output should be the maximum level (around 7.5V for 9V input). Next, LM741 is used to compare the output with a preset voltage level.

When the DPDT switch is in X position the ADJ pin is connected to ground and the (-)ve input of 741 is connected to R4. The potential divider R3+R4 gives about 1.37V at (-)ve input of 741 which is compared with the output from the Voltage Regulator IC. In this case it should be about 1.2V which less than 1.37V hence the output of 741 remains low and the green LED glows. If for some reason the output from the voltage regulator IC is more than 1.37V the output of 741 goes high and the red LED lights up, indicating malfunction of the v/reg IC.

When the DPDT switch is in XX position the ADJ pin is connected to R1 and the (-)ve input of 741 is connected to R5. The potential divider R3+R5 gives about 8.1V at (-)ve input of 741 which is compared with the output from the Voltage Regulator IC. In this case it is should be about 7.5V which less than 8.1V hence the output of 741 remains low and the green LED glows. If for some reason the output from the voltage regulator IC is more than 8.1V the output of 741 goes high and the red LED lights up, indicating malfunction of the v/reg IC.

If none of the LEDs glows, it indicates that input pin and ADJ pin of the voltage regulator IC is short because the +9V are connected to ground via ADJ pin.

An 8-pin IC base or simply a 3-pin female connector may be used to hold the v/reg. IC for testing.

Designed, Written and Submitted by: Abu-Hafss

Real Time Activated Water Level Timer Controller Circuit

An automatic water level timer controller circuit which responds to a real time clock input is discussed in the following article. The design also includes a water detection stage which makes sure the initialization takes place only in the presence of water in the tank or the pipe. The idea was requested by Miss Soumya Mathur.

 The Request

Hi Swagatam Sir,
i m ur biggest fan. m in final yr of my b.e. in electronics & all i can say i will b soon engg. bcoz of u only. i make my each & every project form your guidance. i
passed by 3rd yr only because of u n ur project. u r biggest help of mine. without u n ur idea....m nothing. u teach ur each n every project in simplest possible manner.
each n every student on my batch n even our seniors take help from your ideas n site. u can imagine how famous u r in our college, that college has blocked your site in our
hostel premises LAN n wifi. dats y i access ur site from my cell n writing u mail on gmail.
m in final year n i need ur help in my project. if u don't help, i will FAIL in my project. ur Semi Automatic Water Level Controller/Timer Circuit
( is already made by one of our seniors. m planning to modify it a bit. PLEASE
HELP ME". m planning for something different which is as follows :
1. on/off timer : it should have on/off timer. it can be real time (i.e. like alarm in cell) or simply fixed time (i.e. like on timer in tv). similarly off timer also.
if possible it should give me facility to off my ckt after every 15min till 120 min after ckt is on.
2. water checking : suppose timer is set to 6:00am, den at 6:00am before ckt gets switch on, it should check whether water is available in tap or in tank. if yes, then
only it should switch on ckt, else not. similarly if ckt is set on for 60min (6:00am) n water goes off after 45min (6:45am), then immediately ckt should cut-off n
should switch off pump.
3. i want to run my home pump. i don't understand electrical much but its name plate is written 1.5kw 210V 15Amp.
if u need ny help from me, plz let me know, i wil help u in every possible manner
u can make n post this on ur site. al i expect is jst send me link to my personal gmail id, as i told u ur site is block in our college n hostel premises.
thanks a lot sir in advance
Soumya Mathur 

The Design

The circuit design of the proposed digital clock controlled, real time, automatic water timer/controller circuit may be understood with the help of the following points:

Referring to the diagram above, when a clock positive pulse is received at the input of C2, the circuit consisting of T1 and T2 is latched, allowing the positive 12V to reach the IC1 stage.

The above action powers up the IC1 stage which immediately gears up into a counting mode with an initial zero logic at its pin3.

However the IC1 is able to initiate only in the presence of water in the tank or in the pipe which is detected by T4 through its base sensing plate.

If the presence of water is detected, pin12 of the IC is enabled with a ground signal so that the IC is allowed to proceed with the counting process as expressed in the above discussion.

The triggering clock signal could be from a digital clock alarm output jack or any other similar source which is able to provide a real time based signalling as per the setting of the alarm in it.

Once IC 1 is initiated, it begins counting with the initial status of its pin3 at logic zero.

At this situation T1 is unable to conduct, which allows T2 to conduct triggering the connected relay.

The relay thus initiates by switching ON the motor which starts pumping water across the intended location.

As soon as the counting period of the IC lapses, pin3 goes high switching off T2, relay and the motor to a stand still.

The positive feed from pin3 also reaches pin11 of the IC and the base of T3 which together make sure that the IC gets completely disabled and switched OFF until the next pulse from the real time clock gadget or a cell phone is applied at the shown input of the circuit.

There's one situation that needs to be noted: If a water is absent and not detected by T4, the IC1 will not initiate the motor switch ON and the counting procedures, but T1/T2 stage will continue to be in its latched position and will prompt the procedures to restore as soon as water is detected later on in the course of time. Thus in such a situation the circuit will respond and reset only with the detection of water and not via the input clock trigger. Only once the IC1 counting gets over, and the latch breaks would enable the circuit to respond to a clock trigger for initiating a fresh start as described above.

Parts List for the above explained real time controlled water level timer controller circuit

R1, R3, R6, R11, R12, R13 = 100K
R2, R4, R5, R10, R9, R14, R15, R8 = 10K
R7 = 1M
P1 = 1M POT
R16 = 4.7K
C1 = 100uF/25V
C3 = 10uF/25V NON-POLAR, made by using 10nos 1uf/25v non-polar caps in parallel
C2, C4, C5 = 022uF
C6 = 470uF/25V
D1, D2 = 1N4007
T1, T5 = BC547
T2, T6 = 8050
IC1 = 4060

A Few Doubts as put forth by Miss Soumya (Answers enclosed under the questions)

sir, to be very frank dis ckt is above my expectation. m getting highly confused n not getting ny thing. nw m worried that I don't get failed in xam. ckt is bit complicated for me.

1) if m not rong, grey sq is motor. m rite ??

Yes grey square is the pump motor

2) hw can I trigger clock ? u told via digital alarm clock...but I didn't got hw. plz explain or suggest any other simple way.

A high output could be extracted from the digital clocks IC, or the speaker/piezo or from some relevant point that becomes high when the set alarm is triggered
3) once I trigger clock via alarm, hw can I set time for its operation.

The 4060 timer output can be set by sutably adjusting the variable resistor or the pot at its pin10. This will require little patience and the calibration will need to be experimented through some trial and error.

4) +12V DC supply.... 1 probe wil get connected to 12V battery +ve terminal. wil -ve terminal of battery open ??

-ve of the battery will connect with the line which is connected with pin8 of the IC, anywhere on that rail.

5) can I use common 12v dc battery for both d points.

answered in the previous question

6) off in green color n on in red color...wat r they ??

Those are LED indicators, when green is ON means pump is switched OFF, and when red is ON means pump motor is running.
7) c2,c4,c5 is 22mfd/25v na ??

Those are 0.22uF/50V not 22uF

8) plz elaborate on relay to be used & NC ??

N/C refers to normally closed, meaning the pole of the relay will be connected with this (N/C) when the relay is in a switched OFF state or deactivated state.

Thursday, June 26, 2014

Modifying Car Turn Signal Lights, Park-Lights and Side-Marker Lights

The post explains an innovative circuit modification which allows a single common lamp to be used as a parking light, turn signal indicator light, as well as a side marker light on the relevant positions. The idea was requested by Mr. Chris

The Request

Hello Swagatam. I have a project that is slightly related to this one and could use your help.

I have 2 single filament bulbs that I would like to use as parking lights as well as turn signals. They would be wired to stay on anytime the car is running, and each light would turn off and on when the corresponding turn signal is activated. The wire from factory the turn signal harness controls the +12 side. I also have 2 single filament bulbs that I would like to use as side markers anytime the parking lights are on, and I want them to flash opposite the turn signal, so when the turn signal bulb is lit the side marker is off, and when the turn signal bulb is not lit, the side marker bulb is. The side markers will not be lit unless the parking lights are on, but I do still want them to flash anytime the turn signals are activated. I prefer not to use led's as my project is striving for a retro look, but I might if it's not possible with the incandescent bulbs.

Chris R

The Design

According to the first requirement a single lamp needs to perform the dual function of a turn signal lamp as well as a park light, also the lamp should switch ON as soon as the turn signal switch is turned ON.

The following modified turn signal cum park lamp implements the features exactly as per the above specs.

When the park light is in switched ON position, the TIP122 switches ON the lamp through its base trigger via the upper diode and the series 1K resistor.

Now, if the turn signal switch is triggered, the TIP122 responds by flashing the lamp, while the lower BC547 transistor which also gets triggered with the turn signals makes sure that the signal received from the park light switch is grounded and inhibited from influencing the lamp.

The second requirement demands another lamp which may be positioned as a side marker lamp to respond to the above side indicator or the turn signals but flash with an opposite switching. Also the same lamp is also supposed to light up when the park lights are ON.

The diagram of the enhanced or the modified side marker lamp as shown above satisfies the conditions by flashing the connected lamp with opposite switching, and also responds to the park  switch toggling during normal operations.

The TIP122 is responsible for triggering the lamp when the park lights are switch in.

However when the turn signal switch is toggled, irrespective of the park light input the BC547 begins oscillating in response to the turn flash signals causing the TIP122 to also blink the lamp with the corresponding flash rate.

The 100uF capacitor makes sure that the TIP122 is fed with its stored positive feed for sustaining the illumination on the bulb during the flashing actions.

As per the suggestions from Mr. Chris, the first diagram has been slightly modified with the following couple of improvements:

1) The transistor has been upgraded to TIP142.

2) The park-light input trigger has been replaced with +12V trigger from the ignition key so that the lamp works as fog lights and not as parking lights.

Wednesday, June 25, 2014

Programmable Sequential Temperature Controller and Timer Circuit

Here we learn about a circuit configuration which produces adjustable sequential timing outputs for controlling a heater device through a simultaneously sequencing temperature controller circuit which can be also preprogrammed for acquiring the desired temperature levels across the sequencing time slots. The idea was requested by Mr. Carlos

The Request

Dear Sir,
I’m Carlos and I live in Chile.
As I see that you have the willingness to get us out of trouble with some electronic circuits, I would ask if you have any circuit that controls the temperature and time simultaneously. What I need is a controller with programmable temperature timescales. For example you first hold a temperature T1 at t1 minutes, at the end of this t1 maintains a temperature T2 for t2 minutes after that maintains a temperature T3 for t3 minutes.
The temperature and time should be adjustable in a simple seer either via a PIC or the like, but must be capable of being adjusted without being re-programmed by means of a PC.
I stay eternally grateful.
Best wishes

The Design

The first requirement as mentioned in the above request is a programmable timer which would be able to generate a sequential delay ON periods through a serially connected timer modules.

The number of timer modules and time slots will depend on the user and could be selected as per individual preference. The following diagram shows a 10 stage programmable timer stage made by using 10 discrete 4060 IC stages connected in a sequential configuration.

The design may be understood with the help of the following points:

Referring to the given diagram below, we are able to see 10 identical timer stages consisting 10 nos of 4060 IC arranged in a sequential switching mode.

When the circuit is powered and P1 pushed ON, the SCR latches on resetting pin12 of IC1 to ground initiating its counting process. As per the setting or selection of Rx, 22K and the adjoining 1uF capacitor, the IC counts for a predetermined period after which its pin3 goes high. This high latches itself through the 1N4148 diode and pin11 of the IC

The above high at pin3 of IC1 activates T1 which resets IC2 pin12 into action and the procedure repeats carrying forward the sequence to IC2, IC3, IC4...until IC10 is reached, when T10 resets the whole module by breaking the SCR latch.

Rx may be replaced with a suitable pot for acquiring the desired delays discretely across all the sequential 4060 stages.

The above configuration takes care of the required programmable timing control, however for obtaining correspondingly sequencing timescaled temperature control, we need a circuit that would be able to produce precise, adjustable temperature outputs. For this we employ the following configuration in conjunction with the above circuit.

The shown temperature controller circuit is a simple IC 555 based PWM generator which is able to produce PWMs adjustable right from zero to maximum depending upon a external potential at pin5 of IC2.

The PWM content decides the switching period of the connected mosfet which in turn regulates the heater element at its drain ensuring the required amount of heat in the chamber.

The mosfet will need to be selected as per the heater specs.

The link between this PWM stage and the above sequential timer stage is determined by an intermediate stage made by configuring a common collector NPN device along with a PNP inverter stage, which may be seen in the diagram below:

 Five stages are shown in the diagram which may be increased to 10 numbers for integrating with the 10 stages of the first sequential timer circuit.

Each of the above shown stages consists of an NPN device wired up in a common collector mode for enabling a predetermined magnitude of voltage  to be obtained at their emitters, which would depend upon the setting of the base preset or pot.

All the emitters are terminated to pin5 of the PWM IC2 via separate diodes.

The PNP devices work like inverters for inverting the counting low logic at pin3s of the sequential timer stages into a 12V supply for each of the common collector stages.

The pots here may be adjusted for feeding the preset amount of voltages to the PWM stage which in turn will regulate the PWMs to the mosfet and the heater device, generating the relevant amount of heat for that particular time slot.

Thus in response to the relevant timer stage switching, the corresponding common collector NPN gets activated producing the set amount of voltage at the pin5 of IC2 of the PWM circuit.

Depending upon this preset voltage the heater outputs gets regulated via the mosfet switching.

As the timer sequences, the heater temperature is switched to the next predetermined level as set by the base presets of the above common collector stages.

All resistors in the common collector circuit are 10k, the preset are also 10k, the NPNs are BC547 while the PNPs are BC557