Power Down Alarm

A friend of mine always forgets to put the handbrake on, it’s amazing that her car is ever where she left it. So for Christmas, I gifted her this doohicky.

This little circuit sculpture sits in the car…waiting… suspiciously connected to a USB port. When the car is switched off and it loses power, the hold-up capacitors dump their charge into a Piezo Buzzer and “BEEEEEP”. Consider yourself ‘reminded’ to check the handbrake.

In its simplest form, this circuit is a switch that either connects the capacitor to a power supply for charging, or to a buzzer for discharging. Swap that switch out for a relay whose coil is connected across the power supply and now it will automatically switch between the two when the power goes off. Add a second capacitor in parallel to make it beep for longer, add an LED to indicate when it is receiving power, and turn the whole thing into a circuit sculpture to make it look interesting.

A great excuse to dip my toes into some circuitry and learn something new, and scare a friend along the way.

Lessons Learned