I am trying to reverse engineer a fingernail hardening device for rapid hardware prototyping (becoming some kind of hardware developer I guess)

Since it is a fucking mess (all cables are black) they've chosen a weird construct to operate microcontroller on 240Vac (seems to be possible and made in very low energy consuming devices) i do not find any datasheet for one of the used products. It would help a lot but no. And messing around with high voltage is no fun.

I'm unsure if this fits as a dev rant since most/all I've read so far are software-related.

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    It fits. Welcome to devRant!
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    Let me give you your first incrementation
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    Good to see another hardware dev! One thing you can be sure of though, they're not running the uC at 240V AC. Invest in a multimeter maybe..
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    @tinkrmind yup and an isolation transformer ;)
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    Arent they using uv light for hardening?
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    @stop it does look a lot like a few CFLs in a box. The choke would make sense with that as well.
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    @tinkrmind yepp, that's obvoius. I measured 5v but do not see any voltage regulator or something similar. It looks as if they've implemented a simple voltage divider with diodes and capacitors. I've googled around to find it seems to be common for simple circuits (atiny13 switching a thyristor). But since I have no datasheets for the lamp-inverters it's like poking in the dark. Plus the respect for HV.
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    @potatofriend yeah capacitor divider circuits are very common in cheap electronics. Had a headlamp that used it for charging via AC. Much lighter and cheaper than transformers. Is the microcontroller for auto switch off or some such?
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    @tinkrmind yes, I think there's a simple timer started via push-button (maybe interrupt?) opening a thyristor. I wanted to make the timer varying and settable with rotary encoder and a nifty lcd. So there the atiny is too small. Since i have sample ac/dc converters to 12vdc and buck-converters it should be fairly easy to swap the whole system.
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