Wiparat Circuit Electronics

This is a single zone alarm - with independently adjustable Exit, Entry and Siren Cut-Off timers. It will accommodate the usual types of normally-closed input devices - such as magnetic-reed contacts, foil tape and PIRs.
When the alarm is activated - the Siren will sound for up to 20-minutes. Then it will switch off - and [...]

A 555 timer can be used to generate a squarewave to produce a negative voltage relative to the negative battery terminal. When the timer output at pin 3 goes positive, the series 22 uF capacitor charges through the diode (D1) to about 8 volts. When the output switches to ground, the 22 uF cap discharges [...]

This is a low power voltmeter circuit that can be used with alternative energy systems that run on 12 and 24 volt batteries. The voltmeter is an expanded scale type that indicates small voltage steps over the 10 to 16 volt range for 12 volt batteries and over the 22 to 32 volt range for [...]