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funny story, i just spent a day troubleshooting why a microcontroller would not reset after cutting its power lines turns out it was leeching power from anothe
by jareklupinski 5y ago
funny story, i just spent a day troubleshooting why a microcontroller would not reset after cutting its power lines
turns out it was leeching power from another still-active device through its data pins!
there was not enough power flowing through this way to actually do something, but there was enough to keep the brownout detector from kicking in and resetting the chip
- formerly_proven 5y agoI mirrored the pinout of an AVR once and spent a few hours debugging why ISP wasn't working (so I unsocketed it for programming) and all the pins were wrong. It worked just fine pulling ground and Vcc from the I/O pins just opposite. These are of course fairly low-power 1.8-5 V devices, so when run on 5 V there is a huge margin for the supply voltage.
- phaker 5y agoYou were powering it through the protection diodes. Some 10-15 years ago someone built dirt simple radio tags this way. Just a microcontroller, with a capacitor and an antenna trace connected to some io pin. I loved that hack.
- a1369209993 5y agoTo be fair, the 'correct' way to do this is to use a double-pole switch that actively pulls (whole-device) VCC to ground when off, but that has it's own problems, especially if any of your sensors are capable of generating electricity on their own (piezoelectric microphone, radio reciever, alleged photo'transistor's that can operate photovoltaicly, etc).
- klysm 5y agoThe amount of energy generated by the microphone is gonna be crazy small