consists of a set of ultrasonic receiver and transmitter which operate at the same frequency. When something moves in the area covered the circuit's fine balance is disturbed and the alarm is triggered. The ultrasonic circuit is very sensitive and

Here is a simple 12 V inverter for using a small soldering iron (25W, 35W, etc) in the absence of mains supply. It uses eight transistors and a few resistors and capacitors. Transistors T1 and T2 (each BC547) form an