Hey, Fediverse, EE question here.

I'm building a solar powered night light. I.e. if the solar panels are dark, light should switch on (Digispark with WS2812b). The charger module needs a LOW signal of 30ms..2s to power up its output (normally via button).

Now my question: Is there any circuit that pulls its output LOW for 30ms..2s (and then back to floating or HIGH) as soon as its input drops from ~2.5V to 0V (due to solar panel controller logic)?
Is there some RC magic to achieve that? ^^

@anathem My first thought is an op-amp based comparator, maybe with hysteresis.

@buo Problem is, I don't have a reliable power source for the opamp at that time.
There might be an internal pull-up on that pin of the charger IC that I need to pull down, but apart from that the only power source would be the raw battery voltage -- which must not be deeply depleted, so the circuit must not draw any current when not pulsing...

@anathem Maybe some kind of flip-flop or latch then? Those can activate on negative edges or levels. With some clever feedback you could get them to go from high to low to high. I don't know know if it's possible without a power source of some kind, though.

@anathem normale "Klingelschaltung" sollte das können glaube ich. Die haben selbst-resettende Flip Flops drin - also lösen normal mit einem Puls aus auch wenn man gedrückt hält. So resetter sich das mit dem Lauf der Sonne am nächsten Tag automatisch 😅

@Drezil Die Flipflops brauchen dann aber ne noch ne eigene Stromquelle, oder? Die hab ich eben nicht zur Verfügung dann...

@anathem set an rs flip-flop with the signal from the solar reset it when its charging again and then generate a single pulse from the output

@hausaffe I don't see how that would work, I couln't follow ... also, I don't have any reliable Vcc for the RS-FF IC.

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