EM interference and xenon flash bulbs

I’ve started looking at bumblebee flight paths (especially during initial orientation flights from the nest). To this end I’ve wanted to increase the acquisition frequency of the system.

I found that firing more frequently than about every 1.6s seconds lead to marked decreases in the actual brightness of the flash. Instead I’ve rebuilt the electronics to allow the flashes to be fired sequentially. I have previously done this but found often the flashes would end up firing together. I assumed my circuit had a short, but I found the same happened again in my new circuit. I experimented for a while adding various capacitors across the supply rail (thinking maybe there was a ‘spike’ coming back through the two trigger wires from the flash), with the same thinking I added a reversed diode across those lines to catch any such spike. None of this helped.

I eventually found that spreading the flashes out across my desk helped a lot… this wasn’t expected, and suggested the problem was likely to be electromagnetic interference. The flash going off involves considerable current*, which even given the small size of the flash probably will equate to quite a large whole-spectrum EM pulse.

After chatting with helpful people on freenode’s ##electronics, I tried out tin-foil, and found (as long as each flash & wire was wrapped in its own foil & not touching) the 4 flashes would fire independently.

Quick foil experiment!

I’ll try out using some household build thermal insulation tape to shield the flashes next as that will be a little more tidy. I also found direct sunlight got the black casings quite hot so they will probably benefit from the silver foil for that reason too.

*back of the envelope calculation: If the flash (at 1/32) is abour 3J over 10us (=300kW) with say, 300V across it, then the current will be on the order of 300kW/300=1kA.

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