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I have a vibration sensing alarm circuit here. I want to build in a switch, which should act like a reset switch. It should stop the buzzer from sounding, the LED from emitting light and decharge the capacitor. I tried many time but couldnt find the right place to place the switch. The fist swtch on the right is the main switch, the push to make switch is the vobration switch. By the way, it has got to be a standard SPST on/off switch. Please help, urgently needed!

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You use pin 4 the reset pin, and it's always a good idea to add a 10nf capacitor between pin5 and ground and a 100nf capacitor across the power supply.

I've made these changes for you, notice I've changed the positions of pin 4 and 8 to make it easier to draw.


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The 100nf accross the power supply is always agood idea for any circuit because when the circuit switches (in the case with the 555 it's totem pole output) it can suddenly draw a larger current than normal. The inductance and internal resistance of the power supply can cause the power supply voltage to drop a couple of volts for a few miliseconds, the capacitor stores energy and supplys the power to the circuit during this small power cut. The capacitor on pin 5 (control voltage) keeps the voltage on the internal comparators (which is also from the power supply) in the 555 above the voltage on the timing capcitor during these small power cuts, thus avoiding false triggering.

Sorry I'm a bit drunk at the moment, ;D I hope I've explained this clearly enough, please tell me if I haven't.

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