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/diy/ - Do It Yourself

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>> No.1617098 [View]
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1617098

>>1615963
Noob here trying to understand the schematic for an LED hourglass kit I've purchased.

I've managed to figure out how most of the circuit works, but I can't understand why they chose to use a 4069 hex inverter to make a hacky pulse generator instead of using a 555. Is there something I'm missing here that would mean a 555 wouldn't work? As far as I understand the 555 is designed to properly compare voltage levels of the discharging capacitor, whereas this relies on transitioning between logic high and logic low, purposefully transitioning through the indeterminate region, which I imagine would cause inconsistent behaviour / timing.

Full schematic is here but my screenshot includes everything that's relevant:
https://files.banggood.com/2017/18.01/EH-30-Electronic-hourglass-kit.pdf

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