Reading several blogs about High Altitude Balloon launches in Australia, it appears I may need a way to cut the payload free from the balloon mid flight.

This will ensure that the payload doesn’t travel into a unrecoverable location such as the ocean or dense scrub, but more importantly it can be terminated if the payload looks like it may land into a densely populated area.

I plan to build a cut down circuit and control it via a 2nd Arduino. I’m hoping to be able to transmit a tone such as DTMF to the Arduino and have it trigger a current through some nichrome wire.

I’ve found a cut down circuit on Bovine Aerospace and have built a trial system.

Cut Down Circuit
Circuit from Bovine Aerospace

I have tested some AA’s in parallel to get approx 6v’s with a higher current, which seemed to be enough to heat the wire. However the current was over 2 Amperes and I only had a small relay capable of 2 Amperes and it became damaged. I have since upgraded to a relay that supports more Amperes and everything seems to be working again.

Cut Down Testing
Cut Down Testing

The first test I ran was using some baler twine with a milk bottle on the end. The milk bottle was approx 3 Kg for this test. I’m still yet to confirm if the AA’s are the best batteries for the job, maybe I need something more compact or more current to get the wire glowing red hot.

This is already being activated by the Arduino using a digital output but I am still yet to implement a receiver based activation. I also still need to determine the best way to trigger it.