Return of the dreaded disease

Last night as I making for algorithm changes to my lightning detector, I experienced an unexpected reboot. Never mind, I was probing with a scope lead at the time. That likely caused the problem. But after a few minutes it became clear that I had a problem. The same problem that scuttled my sailboat race start timer.

With small simulated lightning bolts, the unit works fine, but with a large simulated bolt, the processor reboots. A quick look shows a glitch on the 3.3V supply to the micro. I added a cap close to the + and – pins of the processor but that did not correct the issue. I am going to guess that the way to solve this issue are decoupling caps close to the two opamps. I am sure with large pulses, these must need lots of power and pull the power rail down.

But what size caps do I need? This is one place my knowledge fails me. I tend to just “goof around” till it works rather than knowing how to make the appropriate calculations for the correct size caps. Need to learn how to do this. It would not only benefit this project, but perhaps I can get my sailboat race timer working as well.

Any advise on where to learn these skills would be most welcome.

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