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Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

May 26th, 2010

Simple Touch Switch Circuit

Circuit Description

Here is the circuit diagram of touch switch circuit using timer IC NE 555. As the name says this circuit is based on NE 555 IC. This circuit is a simple touch plate controller which when touched on the touch plate operates the relay for a preset time then turns off automatically. This circuit has got applications in common equipments like touch operated doorbells, toys, buzzers etc.

The trigger pin of NE 555 has high input impedance. This property is exploited in this circuit in such a way that human body induced voltage is used for triggering this IC. When this IC is triggered, its output goes to high for a time duration determined by resistor R1 and capacitor C1. The relay used here is driven by a transistor. This relay contact is utilized here to drive loads like bell, lights, motor etc.

Circuit Diagram

Simple Touch Switch Circuit
Simple Touch Switch Circuit

Notes

  • Use a good quality PCB or common board to assemble this circuit.
  • Use an IC holder for mounting the IC NE 555.
  • Cut a 1 square cm thin metal sheet to make the touch plate.
  • To setup the circuit connect to power supply and¬†adjust R1 while keeping touching on the touch plate and stop at the point where relay activates.
May 26th, 2010

Simple Lamp Flasher Circuit

Circuit Description

Here is the circuit diagram of Lamp Flasher using NE 555. As the name says the heart of this circuit is the timer IC NE 555. This circuit is operating from 230V AC mains. In this circuit, the timer IC is wired in such that it works as astable mutivibrator. This astable multivibrator circuit produces pulses for flashing the lamp. The duty cycle of the pulse can be varied by using the resistors R2 (47K) and R3 (10K). As the duty cycle changes the rate of flashing also changes accordingly.

The power supply for timer IC is half wave rectified output that is taken through diodes D1 and D2. The triac T1 (BT 136) is used to drive the load L1. The triac T1 is driven by the transistor Q1 (BC 548). The 1K resistor R4 is used here to limit base current of transistor Q1.

Circuit Diagram

Simple Lamp Flasher Circuit

Simple Lamp Flasher Circuit

Notes

  • Use a good quality PCB or common board to assemble this circuit.
  • Use an IC holder for mounting the IC NE 555.
  • If frequent changes in rate are needed, replace resistor R2 with a 100K potentiometer.
  • Intensive care should be taken while dealing with this circuit since many parts of it are live with potential shock hazards.
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