General purpose circuit of the simple pressure sensor alarm is built around a couple of readily available cheap components. Working of this circuit is straight forward and self-explanatory. When the circuit is powered by a 9V compact battery, the active piezo-sounder at the output of IC1 starts beeping for a short time and then goes into idle state.
Whenever, the pressure sensor element (Piezo-ceramic wafer) is gently tapped, mosfet T1 is fired by the electric pulse from the sensor through related components and IC1 is again enabled by T1. As a result, the piezo-sounder starts beeping for a short duration, set by the in-circuit values of R3 and C2. Piezo-sounder at the output of IC1 can be replaced with a low current 6 to 9 V electromagnetic/solid-state relay to control external loads. Likewise, values of components T1,R3 and C2 are not very critical.
You can experiment with another values to “tune” the circuit as per your requirements. Pressure sensors (in piezo-wafer form) are widely available with reputed hobby electronics components dealers.
Possible Applications of this pressure sensor circuit:
Automatic Door Bell, Carpet Alarm, Hit Switch, Knock Bell, Garage Alarm, Doormat Sensor…