Perplexing circuitry
Added 2023-08-05 13:59:23 +0000 UTCOn one hand, this circuit could have a glaring defect, but on the other hand the microcontroller could theoretically contain an independent simple shunt reference of about 0.6V below the lithium cell's maximum voltage.
I won't release this video until I can prove my thoughts, as it would be inappropriate to diss a product as being potentially dangerous when it just had an unusual design quirk.
https://www.youtube.com/watch?v=pvH54RVZ2sw
Comments
Consider me perplexed too, Clive! What if we call the connection to the top left NPN base charge, the one to the right of the on/off switch Vi, and the chip /not/ a microcontroller. I think it's more analogue than that. If the charge input has an NPN with the emitter to ground and collector to charge input, plus a resistor from charge to its base. If the switch is off, the charge input is kept low and the battery never charges or discharges. The solar cell can float high when lit and not source much current. Then if the Vi input has a PNP with a suitable base resistor and limit resistor it can pull the charge input high to allow the battery to charge, and add a 3V9 zener across the first NPN so it doesn't charge above 4.2V. Add a small state machine to control brightness using PWM, and another transistor & zener so if Vi drops too low there's something to turn the LED output off. Does any of that make sense? It wouldn't use much silicon area.
Nigel Walker
2023-08-08 15:48:08 +0000 UTCWhat about measuring the resistance from 0v to the mystery IC connection when the switch is off. Does it get pulled to 0v? (Sorry if I missed you doing that.)
Dave Haans
2023-08-06 16:45:27 +0000 UTC
