Simple Electronic Doorbell Circuit Using Counter

This is a simple design circuit for a door alarm circuit, but in this design using electronic system. This circuit uses a synthesized sound chip from Holtek, the HT-2811. This circuit reproduces the sound of a "ding-dong" chiming doorbell. Additionally, the circuit includes a CMOS 4026 counter display driver IC to count your visitors. This is the figure of the circuit.


The operating voltage must remain within 2.4 to 3.3 VDC and standby current is minimal. The reset switch zeroes the count, and the 7 segment display is a common cathode type. To save power consumption the display can be enabled or disabled with a switch as shown in the above diagram. The count will still be held in memory.

The envelope of the chime is set by the 220k, 330k, 3u3 and 4u7 resistors and capacitors. These values are the manufactures default values, but may be adjusted to alter the length and delay of the chime. The combination of the 2k2, 22k and 47u resistor capacitor network has a double function. It provides a de-bouncing circuit for the bell press and at the same time has a sufficiently long time constant. This ensures that anyone rapidly pressing the doorbell switch, only advances the count once. The 47u capacitor may be increased in size, if needed.

Pin IC CMOS can look for the list below.
Pin 1 is the clock input
Pin 2 is the clock enable
Pin 3 is display enable
Pin 4 enables the carry output
Pin 5 is the carry output
Pin 6 is display segment f Pin 7 is display segment g
Pin 8 is 0 V.
Pin 9 is display segment d Pin 10 is display segment a
Pin 11 is display segment e Pin 12 is display segment b
Pin 13 is display segment c Pin 14 is the2 output
Pin 15 is reset
Pin 16 is +Vcc

Simple Light Sensor Circuit Using Op Amp

This is a one of the light sensor. This circuit is a dark sensor that is based on op – amp 741 IC as main control. This circuit is a simple design for sensor the light at the night. This is the figure of the circuit.


For sensor the light is using LDR. Operation of the circuit is under normal conditions the resistance of the LDR is high, keeping pin 2 low. When light falls onto the LDR the resistance drops to a couple hundred ohms and triggers pin 2 high which biases the base of Q1 via pin 6 and R4 and in turn activates the relay. Trimmer pot P1 and the two 470 ohm resistors, R2 and R3, are a voltage divider to adjust for sensitivity.

If you want the action reversed (make it a dark sensor), change the positions of the LDR and R1. If the relay 'chatters', add a bit of hysteresis by adding a 100K to 1Meg-ohm resistor (R6) over pins 6 and 2 of the 741 op-amp, but in most cases 100K to 330K will do the job. The LDR is a regular, general purpose type. D1 serves as a spark-arrestor when the relay contacts open. This circuit power supply is using 12 V DC.

Simple Cascaded Timer Circuit

This is a simple design circuit that uses a CMOS dual re-trigger mono stable IC 4528 in a cascade timer circuit. The CMOS timer can be easily cascaded with other similar 4528 circuits to lengthen the timing needed. This is the figure of the circuit.


The timing of the project is determined by VR3 and C1 for the first stage and VR4 and C2 for the second stage. Once button S1 is pressed, the 1st stage output pin 6 logic level will go high and output pin 7 will go low for the preset time which is determined by VR3 and C1. When the time is up, the output pin 6 will go low and pin 7 high. At this moment of time, pin 7 will positive trigger the 2nd stage of the timer at pin 12. Output pin 10 will go high and pin 9 will go low for a time determine by VR4 and C2 before the cycle end with pin 10 back to low and pin 9 to high.

Simple White-LED Flasher Circuit

This is a design circuit for flasher LED. This circuit flashes an LED to provide a highly visible warning signal—for example, to indicate power on, battery low, or another eye-catching visual signal. However, white LEDs typically present a forward - voltage drop of 3 to 5V. This circuit is work with based on Logic IC and two transistor as main control. This is the figure of the circuit.


The principle of the operation in this circuit is when IC1’s output pulses high, Q2 turns on and saturates, sinking current, IL, through inductor L1. The inductor current ramps up at a rate determined mainly by VBATT; L1’s inductance; and Q2’s on-time, tON. During this interval, LED D1 and Q1’s base-emitter junction are reverse- biased. Provided that the inductor does not saturate, current IL ramps up linearly and reaches a peak value, IL(PEAK) at the end of the on-time. When IC1’s output goes low and Q2 turns off, L1 generates back EMF to forward-bias D1 and raises its anode voltage, VA, to a value greater than VBATT. Current circulates through L1 and D1 and ramps down to zero as L1’s stored energy decays. Values of 100 pF for C2 and 220 k_ for R2 set the astable oscillator’s frequency at approximately 20 to 30 kHz.

Simple Thermostat Circuit Using LM358

Thermostat is one of the common device used to control the temperature of a space be it a warehouse, a room, a hall or an office. This thermostat circuit will focus on the heating control of a space that uses electric heater as its source of heating. It basically consists of a comparator that controls the ON and OFF of the electric heater based on the sensor temperature. This thermostat is based on op-amp LM358 to control the operation this circuit. Look this figure of circuit.


The LM358 op amp is used as a comparator to sense the inputs of the reference voltage (PIN 3) and room temperature (PIN 2). The thermistor used is a NTC (negative temperature coefficient) type where its resistance will drop when the temperature increases and vice versa. It has a resistance of 20K ohm at 25 degree Celsius. When the room temperature drops, the thermistor resistance will go up and hence the output of the operational amplifier will be low. This cause the relay to turn OFF and the heater will conduct until the temperature of the room rises again. To calibrate this circuit, we using variable resistor VR1. Set the lever of the slide potentiometer or rotary potentiometer VR2 to 25 Celsius location. Place the thermistor at a space where the temperature is at 25 Celsius. By varying VR1, set the resistance at the position between the ON and OFF of the relay. Use a suitable contact relay rating according to the load of the heater.

Simple Inverter Circuit for Florescent Lamps

This is the design for simple inverter circuit. This circuit is very easy and inexpensive to construct, reliable, and enough powerful to light up a 15 W florescent tube lamps. This circuit is based on a transistor NPN bipolar. This is the figure of the circuit.


The only hard-to-find piece of this baby is the so-called yellow inverter transformer. It's a miniature high frequency transformer that has a 25mm x 20mm x 5mm ferrite core, 30 turns of primary, 15 turns of feedback, and 250 turns of secondary all concentric, wound on plastic frame than wrapped with a 'yellow' adhesive tape. The transistor that is used in the circuit is 2SD882. This is a single transistor oscillator circuit. Current passed through primary winding inducts a magnetic field to the core and the core gives the energy back to the feedback winding with a delay determined by the core material and windings. System then oscillates continuously on a frequency depending on this timing.

Simple High Gain Amplifier Circuit with Transistor

This is a design circuit for gain amplifier. This circuit is using transistor to control the operation. This is the figure of the circuit.


The transistor is a current amplifying device and it will amplify the base current by at least 200 times. The diagram below will assist you to see this. The resistance between the collector and emitter leads of the NPN transistor reduces and a "turn-on" circuit is produced for the PNP transistor by the action of the NPN transistor, combined with the 1k resistor. These two components form a base-bias resistor for the PNP transistor and the base of the PNP is turned on. This causes the PNP transistor to turn on and current flows through its emitter-collector leads. The actual gain of the PNP transistor is about 50 - 100 and depends on the current through the load. In series with the emitter-collector leads of the PNP transistor is a LED and 22R resistor and the current that flows through this circuit causes the LED to illuminate.

Simple DC Converter Circuit 5V to 10V

This is design circuit for converter in DC voltage. This circuit can work to convert voltage in 5 – 10 Volt. The circuit is work based on IC MAXIM. This is the figure of the circuit.


The MAX889T voltage inverter, IC1, converts a positive input to a negative output voltage with an absolute magnitude lower than that of its input. But, in this circuit, Schottky diodes D1 and D2 and capacitors C4 and C5 help produce a higher output voltage. The circuits nominal output is VOUT = (2xVIN − 2VD − IOUT−RO), where VIN is the input voltage, VD is a diode’s forward-voltage drop, IOUT is the output current, and RO is IC1’s output resistance in free-running mode.

Simple Voltage Regulator Using LM317

This is a design simple voltage regulator power supply. This circuit can be used to power the two way mobile radio from the car cigarette lighter circuit. The circuit is based on LM317 IC as regulator voltage and should accept up to about 14 volts without problems. It can handle up to 1 amp, but this circuit will need a heat sink on the voltage regulator. This is the figure of the construction circuit.


This circuit needs some component in this list:
R1: 270R
R2: 2K Cermet or carbon preset potentiometer
C1: 100nF
C2: 1uF tantalum
LM317T Voltage regulator Heat sink
PCB board

In this circuit added DC power jacks for input and output on my voltage regulator, a green power LED, and a red over-voltage LED. The over voltage LED uses a zener diode to switch on the LED at a certain preset voltage, this can be varied depending on the voltage of the zener diode, I used a 6.2v zener diode. You can even add a relay to switch off the power if the over voltage LED turns on, but bear in mind it will have to work from the voltage of the zener diode right up to the input voltage.

Simple Thermistor Triggered Switch Circuit

It is a simple design circuit for thermistor triggered switch using adjustable threshold. This circuit is triggered with cold temperatures that may be used as frosh alarm or cold temperatures switching. This circuit working with based on op-amp 741. This is the figure of the circuit.


In this circuit, temperature that is used resistance of 15k at 25 degrees Celsius and 45k at 0 degrees Celsius. For operation the circuit, it is begin with function of the op-amp. In this circuit, the op-amp is used as comparator. Pin 3 in the op-amp is used as biased to half the supply voltage. The non-inverting input is connected to the junction of the thermistor and potentiometer. The control is adjusted so that the circuit is on when the thermistor is at the required temperature range. A slight amount of hysteresis is provided by inclusion of the 270k resistor. This prevents rapid switching of the circuit when the temperature is near to the switching threshold.

Simple Telephone Status Indicator Circuit

This is a simple design circuit that can be used as a telephone status indicator. This circuit is work with based on two transistor. This is the figure of the circuit.


When the telephone is in use (off hook) the transistor Q1 switches ON making the red LED D2 glow. When the telephone is not in use (on hook) the Q1 turns OFF and Q2 turns ON. This makes the red LED D2 off and green LED D3 ON. The circuit is powered from the phone line itself and no external power supply is required.

Simple LED Flasher Using Transistor

This is a circuit that has function as LED Flasher. This circuit will flash a bright light of the LED (5000 mcd) to take attention getting devices to the alarm. This circuit is work with based on the two transistor as the control of the circuit. The component value that we used is not a critical component. This is the figure of the circuit.


Flash duration in the circuit is determined by R2 and C1 and it is approximately 3 time constant. For control the brightness of the LED by R3 with limits 20 milli ampere. R1 is provide bias for the transistor.

Simple 3 Amp Power Supply Circuit

This is a design for simple regulated power supply. This circuit can adjust from 3 to 25 volt and it is current limited to 2 ampere. In this circuit, the current limited can increased to 3 ampere or more with select a smaller current sense resistor. The circuit can operate with based on two transistor and regulator IC LM1558. This is the figure of the circuit.


Operation of the power supply begin with Voltage regulation is controlled by 1/2 of a 1558 or 1458 op-amp. The 1458 may be substituted in the circuit below, but it is recommended the supply voltage to pin 8 be limited to 30 VDC, which can be accomplished by adding a 6.2 volt zener or 5.1 K resistor in series with pin 8. The maximum DC supply voltage for the 1458 and 1558 is 36 and 44 respectively. The power transformer should be capable of the desired current while maintaining an input voltage at least 4 volts higher than the desired output, but not exceeding the maximum supply voltage of the op-amp under minimal load conditions. The power transformer shown is a center tapped 25.2 volt AC / 2 amp unit that will provide regulated outputs of 24 volts at 0.7 amps, 15 volts at 2 amps, or 6 volts at 3 amps. The 3 amp output is obtained using the center tap of the transformer with the switch in the 18 volt position. All components should be available at Radio Shack with the exception of the 1558 op-amp.