Paste your Google Webmaster Tools verification code here
Browsing Category: "Circuit Diagram"

High and Low Voltage Cut-Off with Delay and Alarm

28th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
Simple and easy build High and Low Voltage Cut-Off with Delay and Alarm Circuit. This straight forward circuit will protect electrical appliances from over voltage as well as under voltage. The circuit also produces an alarm when the power supply comes back. An ideal circuit for home to protect your valuable equipments from voltage fluctuations. The same circuit with some modifications can be used  to make a automatic voltage stabilizer.

High and Low Voltage Cut-Off with Delay and Alarm Circuit Diagram :

Alarm Circuit Diagram

When the mains voltage is in the normal level, the voltage at the negative terminal of zener diode D4 will be less than 5.6 Volts. At this condition transistor T1 will not conduct. The same time voltage at the negative terminal of zener diode D5 will be greater than 5.6 and so the transistor T2 will be conducting. The relay will be activated and the green LED will be glowing.

When the mains voltage is higher than the set limit the transistor T1 becomes conducting since the voltage at the negative terminal of  D4 is greater than 5.6 V. At the same time transistor T2 will be non conducting which results in the deactivation of relay to cut the mains supply from load. When the mains voltage is less than the set limit transistors T1 & T2 becomes non conducting  making the relay to de-activate and cut the load from mains.

The timer NE555 is wired as a monostable multivibrator with a pulse width of 10ms.When the power comes back after a cut off a negative voltage is obtained at the trigger pin which triggers the IC NE555. The transistor T3 gets forward biased and it drives the buzzer to produce a beep as an indication of power resumption. Also the transistor T1 is made on which in turn makes T2 off. As a result the relay will remain de- activate for 10ms and this provides the sufficient delay and the equipment  is protected from surge voltages.

Notes :

  • To calibrate the circuit a autotransformer is needed. Connect the output of autotransformer to the transformer primary.
  • Set the voltage to 260V and adjust  VR1 to make the relay deactivated.
  • Now set the autotransformer to 160V and adjust VR2  so that the relay is de-energized.
  • VR3 can be used to vary the volume of buzzer.

Alarm Signal Generator IC ZSD100 Datasheet, Application Circuits

27th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
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

Underwater LED Boost Converter with Dimmer Circuit

27th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
The post discusses an LED controller circuit having a boost and dimming facility specifically designed for underwater shooting application. The idea was requested by Mr. Svein.

The Request

Hi Swagatam,


I came across your blog at homemadecircuitsandschematics.blogspot.com and thought I’d ask you a question regarding building or modifying a LED driver.

I planning to build a LED underwater light with a 100w LED SMD.

For the LED module I’m planning on using one of the following types:
New100W-LED-Chip-Cool-White-High-Power-SMD-LED-Panel-9000LM-Lamp-For-Flood-Light
or 
CREE-XLamp-XPG-XP-G-100W-Cool-White-LED-SMD-Light-Emitter-Chip-Solid-Copper-Base
For the driver I’m looking at one of the following:
DC-DC-100W-Constant-Current-Boost-Step-up-Module-Mobile-Power-Supply-LED-Driver
or
100W-LED-Driver-DC12V-24V-Input-DC30-36V-3A-Output-for-100W-LED-Light-Lamp-Bulb
or
100W-DC-DC-Boost-Adjustable-Power-Converter-LED-Driver-Constant-Current-Voltage
I need the driver to boost/step up voltage from 11-13v to the required voltage of the LED module, and in this case that would be 30-36V and of course be able to current limit the output.

But what I also want, that none of the drivers listed above provides is being able to dim, or set maybe 3 to 5 different intensities like 10%, 30%, 50%, 70% and 100%. I would also like the driver and on/off-function to could be controlled by a reed/magnet switch to avoid running a switch through the watertight casing. Keeping the size down is also beneficial. 

Is there any way you would think it is possible to modify the drivers listed? Or is it possible to build something like this by myself?
If you do have the time to consider a circuit like this it could be very helpful.

I am planning to have two separate light heads with one 100W LED SMD in each, and run them from the same battery. It is for video lights, so one light on each side of the camera. If the control of these two lights could be controlled by the same switch it would be nice also 🙂 

Great site btw, thank you for sharing all your information!

Kind regards,
Svein

The Design

The proposed LED underwater light booster circuit with dimming feature could be build using a few 555 ICs as presented in the following description and the above circuit diagram:

The design is basically a controlled PWM generator circuit using a couple of versatile 555 ICs.

The one on the left is rigged as an astable for producing a high frequency square wave which is fed to the complementary IC2 555 stage wired in its standard PWM generator form.

IC2 responds to the fed pulses at its pin2 and compares it with the potential at its pin5 as set by the attached 10k preset.

The potential at pin5 set by the 10k preset voltage divider determines and varies the output PWM content at pin3 of IC2 by proportionately varying the duty cycle of the PWMs.

Lower potentials at pin5 of IC2 results in higher space ratio thereby forcing the LEDs to go dimmer and vice versa.

The above PWMs finally is applied to the gate of an N-channel mosfet which transforms the data into an amplified, boosted voltage across the LEDs with the help of the inductor L1.

The mosfet along with L1 forms a simple boost circuit which converts the 12V supply to the required 36V directly across L1 for the LEDs to get illuminated optimally.

The BC547 at pin5 of IC2 is positioned as a current sensor and controller, its base resistor Rx decides the maximum safe current allowable for the LEDs, and may be calculated as per the following formula:

Rx = 0.6/I where I is maximum current limit as per the LED specs.

How to Wind L1

It could be a matter of some experimentation. Begin by winding arbitrarily a few turns of 22 SWG magnet wire over a ferrite rod of any dimension. Connect it with the circuit and measure the boosted voltage across the coil (without connecting the LEDs).

Now simply divide the measured voltage with the number of turns used, the result would give you the turns per volt of the coil assembly. Next, its just a matter of optimizing the number of turns for acquiring the required magnitude of volts, which is around 33V in the proposed under water LED light booster, dimmer circuit.

Variable LED Intensity Controller Circuit

26th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
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.

Simple and Mini FM Receiver

26th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
This is a very simple and mini fm radio receiver with good performances that works great even if the sensitivity is not too high. The working principle of this fm receiver may seem a little unusual. It is made of an oscillator (T2 and T3) that is synchronized with the received frequency of T1. This transistor works as a broadband preamplifier in VHF range.

Mini FM Receiver Circuit Diagram :

FM Receiver Circuit Diagram

The oscillator is adjusted between 87 … 108 MHz with C5. Because of the synchronization, the oscillator output will have the same frequency deviation as the received signal from the fm antenna. This deviations are caused by the broadcasted audio informations. The frequency modulated signal show up on P1 + R5. Low pass filter R6/C6 extracts the audio signal and then is amplifier by T4 … T6 and transmitted at the output through C9 capacitor.

The coil details are presented in the fm receiver circuit diagram. The radio receiver is adjusted on different stations with the help of C5. P1 potentiometer is adjusted untill the best reception is obtained. If we attach an audio amplifier and a speaker then this fm receiver can be made very compact as a pocket radio.

SMPS Welding Inverter Circuit

25th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »

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 36×0.55mm. 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 36×0.5mm. 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:

High Level Wideband RF Preamplifier

25th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
This High Level Wideband RF Preamplifier can be made in two ways: (1) with the aid of a linear active element, or (2) with a non-linear element operating with negative feed-back. This circuit is of the second kind, using an RF power transistor as the active element. Feedback is also required to ensure correct termination (50 Q) of the aerial, since bipolar transistors normally exhibit a low input impedance. Also, the noise figure is not increased because virtually no signal is lost.

High Level Wideband RF Preamplifier Circuit Diagram:

RF Preamplifier Circuit Diagram


The common-base amplifier is based on a UHF class A power transistor Type 2N5109 from Motorola. The feedback circuit is formed by RF transformer Th. The input and output impedance of the preamplifier is 50 4 for optimum perform-ance. Network R3-C5  may have to be added to  preclude oscillation outside the pass-band, which  ranges from about 100 kHz to 50 MHz. The gain is  approximately 9.5 dB, the noise figure is between 2  and 3 dB, and the third-order output intercept point  is at least 50 dBm.

The input/output transformer is wound on a Type FT37-75 ferrite core from Micrometals. The input winding is 1 turn, the output winding 5 turns with a tap at 3 turns.

Capacitor Based LED Tubelight Circuit Using 1 Watt LEDs

24th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
The post explains the construction of a homemade 100 watt capacitive tubelight circuit using 1 watt LEDs. The idea was requested, constructed, tested and verified by one the avid readers of this blog Mr. Tamam. Let’s go through the entire discussion.
Presented below is the email discussion between Mr. Tamam and me.
Dear Swagatam!

At first I want to give you thanks for sharing your vast knowledge on electronics among electronic hobbyist. My name is Tamam, and I am from Bangladesh. It was my long term wish to meet with you face to face, I was about to come in India for a personal work, but a complication in the visa process has delayed the travel plan although I still have plan to visit.

However, I regularly visit your blog, and so far I have constructed several circuits from you blog. It’s been a long time I am trying to build an AC LED Tube light which will run at 220-240 VAC and produce more or at least equivalent light as like a 60 Watt regular tube/florescent light, because I want to replace my room’s tube light which annoy me always. I like LEDs very much because of their low power consumption rate and high brightness. 

I have already seen several circuits related to AC LED lights on your blog, but none are fit to my criteria.

My Requirements:
“”””””””””””””””
1. I will use 1 Watt LED (3.3V, 10mm, 180 degree) a number of maximum 100-150 piece. 
2. Power Supply will be Capacitive Type with maximum protection as far as possible. I don’t want to use transformer.
3. Output light has to be bright as much as a regular tube light (60 Watt) like I said above.

I know it’s easy for you to design a circuit considering above requirements. 
Swagatam, I badly need the circuit, its my humble request to you, please take time and design the circuit for me. 
Sorry for my bad English & Thanks in advance !!
My Reply:
Thank you dear Tamam,
I appreciate your interest, I already have the requested circuit in my blog, please check out the following link:
Best Regards.
Dear Swagatam!

Thank you for your reply. Sorry to bother you bro, I don’t understand “SMPS types NTC thermistor”
Even my local spare parts dealers did not understand. All they asked me for a value in Ohms for the thermistor, is the termistor compulsory for the circuit? Because, I assembled and tested your circuit in project board successfully without the thermistor. If it is not compulsory then I wont use it.

Now about my second requested circuit: Dear Bro, its pleasure to me after knowing that you will design and post the circuit. I always try to keep in touch with your blog. Your blog is full of electronic circuits divided into many categories, like an ocean (just kidding). Sometimes its very hard and time consuming to find new post or a particular circuit in your blog.

All I want to say that, if possible please give me the post link in email just after posting the circuit in your blog. It will be great convenience to me.

Thank You !

Thank you dear Tamam!
You can explain the dealer by saying that you want a thermistor that are normally used in 12V smps adapters. I am not sure about the exact ohms so can’t suggest it correctly.
Alternatively you can simply eliminate the NTC and use an inductor directly in series with the LED chain, this inductor could be made by winding a magnet wire (super enameled copper wire) over any ferrite core, use 100 turns of it with 10mm diameter. The data is not critical could be a little here and there, we simply need a coil having a resistance of 10 ohms in series with the LED…that’s all.

Dear Swagatam,
Thank you for providing your 100 Watt LED Circuit. After some trial and error I have successfully built the circuit but slightly modified your circuit as below:
1. I have used total 96 nos. of 1 Watt high bright worm white LEDs.
2. I have changed the value of the AC capacitor in your circuit from 5uF/400V to 14uF / 400V (After putting total 4 nos. of 3.5uF capacitors in parallel) as I am not getting sufficient light with 5uF/400V. I used bleeding resistor rated 1 Mega Ohms between leads of capacitors.
3. I have also changed the Filter capacitor next to bridge rectifier from 10uF/400V to 100uF/400V and added a bleeding resistor rated 470 Kilo Ohms across its output.
4. I have put a Varistor between incoming AC Neutral and Phase to the circuit.
However, I am posting some images of the project.
The following image presents PCB design layout for the above 100 watt LED tubelight circuit, Courtesy Mr. Abu Tamam.

SMPS Halogen Lamp Transformer Cicuit

24th January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
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.

Water Heater Buzzer Alarm Circuit

23rd January 2016 Cat: Circuit Diagram, Uncategorized with No Comments »
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.