Electronic Circuits and Diagram-Electronics Projects and Design

Description. Many fire alarm circuits are presented here,but this time a new circuit using a thermistor and a timer to do the trick. The circuit is as simple and straight forward so that, it can be easily implemented. The thermistor offers a low resistance at high temperature and high resistance at low temperature. This phenomenon is employed here for sensing the fire. The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output (pin 3) of IC1 is couples to base of transistor T3 (SL100), which drives the speaker…

Description. 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. 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…

Description. Here is a simple variable frequency circuit based on timer NE555. Here NE55 is wired as an astable multivibrator, whose output frequency can be varied by varying a potentiometer. This circuit is a must in the work bench of a electronic hobbyist. Frequencies ranging from several Hz to several KHz can be obtained using this circuit. For very low frequencies (few Hz) replace C with a higher value electrolytic capacitor. The low frequency oscillator schematic is shown below. Circuit diagram with Parts list. Notes. The values of R and C can be obtained using the following equations. 1/f =…

Description. A simple scoring game circuit that can be used for all occasions when a dice is needed.The circuit is based on a NE555 timer,a 74LS192 counter,a74LS247 decoder and a & segment LED display.The timer IC1 will produce the clock for the counter IC(IC2) whose frequency is determined by R1 and C2.When S2 is pressed the IC2 will count in up mode and when S3 is pressed the IC2 will count in down mode.The IC 3 will decode the count to display it on the seven segment LED display .Thats about the working of the circuit.The circuit is designed strictly…

A simple Light to Frequency Converter Introduction. Here is the circuit diagram of a effective light to frequency converter circuit that can be used for variety of applications such as light intensity measurement,fun etc. The circuit is based on TLC555, the CMOS version of famous timer IC NE 555. A photo diode is used for sensing the light intensity.The timer IC is wired in astable mode.The leakage current of the reverse biased photo diode is proportional to the light intensity falling on it.This leakage current charges the capacitance C1.When the capacitor voltage reaches 2/3 of the supply voltage the out…

Description. A dual tone train horn simulator circuit can be made using two NE 555 timers connected in cascade.Here instead of using two NE 555 timers a single NE 556 timer is used which is a nothing but two 555′s in one package and each timers work independently.Switch S1 can be used to start the horn.The circuit is simple and low cost but works greatly. Circuit Diagram & Parts List. Notes Use a 9V DC power supply or battery for this circuit. Assemble the circuit on a good quality PCB or common board.Constructing a bread board prototype is recommended. We…

InfraRed (IR) Sensor/Detector Circuit Description. The circuit shows that the output of IC1 555 IC,which is designed for a duty cycle of 0.8mSec,with a frequency of 120Hz and 300 mA peak current, is used to drive the infra red LED,D1.From the connection it is clear that the diodes D1 and D2 are on the same line,just a few centimeters apart, on the breadboard.Thus diode D2 receives the infra-red output from the diode D1.The diode signal, which is given to the inverting terminal of the op-amp IC LM 358 gets amplified and its peak is detected by diode D4 and capacitor…

Fridge Door Alarm Circuit Description. This is a fridge door alarm circuit, which produces an audible alarm when fridge is left open for a preset time. This versatile alarm is based  on two 555 timer IC’s. Both ICs are wired as astable Multivibrators. An LDR is connected in parallel to the timing capacitor C1 of IC 1.When door is completely close there will be no light inside the fridge and LDR offers high resistance keeping R1 fully charged.When door is left open ,the lamp inside the fridge will keep glowing ,LDR will be illuminated, and its resistance falls. This makes…

Make a Digital Stop Watch Description A digital stop watch built around timer IC LM555 and 4-digit counter IC MM74C926  with multiplexed 7-segment LED display. MM74C926 consists of a 4-digit counter, an internal output latch, npn output sourcing drivers for common cathode, 7-segment display and an internal multiplexing circuitry with four multiplexing outputs. The counter advances on negative edge of the clock. The clock is generated by timer IC LM555. The circuit works off a 5V power supply. It can be easily assembled on a general-purpose PCB. Enclose the circuit in a metal box with provisions for four 7-segment displays,…