Have you ever thought that it would be funny if you had something that could make a big bang in the middle of the night?

Probably not, but I did. I live in leafy suburbia in England and thought a mystery bang now and then would get people talking. It needed to be radio controlled so I could activate it from my bed, it also needed to be battery powered and loud.

I thought about the propane bird scarers that I had seen in fields as a boy, so I did a search to see if anyone had ever built one at home. Sadly there was just one guy who had tried but could not get the gas/air mixture consistent and this resulted in a bang sometimes and just a puff of flame at others.

Undaunted I searched sites of bird scarer manufacturers for manuals and parts lists that may give some clues about their design. I soon found out that it is just a tube with a baffle in it, a jet for the gas and a spark ignitor.

My tube was 4 inch toilet pipe, my jet was a bit of copper brake pipe squashed at the end and my spark plug was two screws and washers. I cut a baffle from some scrap mild steel and bolted in about 18 inches in to the pipe. I used a 4 inch pipe junction to drill a hole for the jet and the spark gap went in the inspection bit at the back.

Control electronics.

A cheap fob receiver for a garage door triggers an electronic timer (RS) that opens a gas solenoid (Ebay) for 35 seconds. This loads the gas from a barbecue propane bottle.

The solenoid output also charges a capacitor. When the timer drops back to normal, this capacitor is discharged into an old xenon beacon PCB. This makes 400V for a few seconds until the capacitor discharges. The 400V is fed into an old electric fence output PCB that manages a couple of sparks across the ignitor gap.

The whole thing is run from 2 old 24AH 12V batteries making the system self contained and good for a month on a charge.

Unit built and ready to go.

gas gun diagram