This is the simple circuit of diagram of a small touch using IC NE 555 . This circuit is ideally useful for making touch operated doorbells, buzzers, toys etc which when touched on the touch plate operates the relay for a preset time and the turns off automatically.
the circuit is realized by utilizing the high input impedance of trigger pin of the IC 555. When the IC is triggered by the induced voltage of human body the output goes high for a time determined by R1 and C1. The transistor is used to drive the relay. The relay contacts can be used to drive the load like bell, motor , lights etc.
To setup the circuit connect to power supply and adjust R1 while keeping touching on the touch plate. Stop at the point where relay activates.If relay is in the activated state initially then do the same until the relay is deactivated.
functions of each pin IC 555
- Ground, is the input pin of the source of the negative DC voltage
- trigger, negative input from the lower comparators (comparator B) that maintain oscillation capacitor voltage in the lowest 1 / 3 Vcc and set RS flip-flop
- output, the output pin of the IC 555.
- reset, the pin that serves to reset the latch inside the IC to be influential to reset the IC work. This pin is connected to a PNP-type transistor gate, so the transistor will be active if given a logic low. Normally this pin is connected directly to Vcc to prevent reset
- control voltage, this pin serves to regulate the stability of the reference voltage negative input (comparator A). This pin can be left hanging, but to ensure the stability of the reference comparator A, usually associated with a capacitor of about 10nF to berorde pin groun
- threshold, this pin is connected to the positive input (comparator A) which will reset the RS flip-flop when the voltage on the capacitor from exceeding 2 / 3 Vc
- discharge, this pin is connected to an open collector transistor Q1 is connected to ground emitternya. Switching transistor serves to clamp the corresponding node to ground on the timing of certain
- vcc, pin it to receive a DC voltage supply. Usually will work optimally if given a 5-15V. the current supply can be seen in the datasheet, which is about 10-15mA.