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Temporary pull-up during boot (ESP-01)
(lemmy.world)
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this post was submitted on 12 Dec 2023
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I’m not entirely clear on the problem, but yes - the circuit as drawn makes the microcontroller pin start high, then fall after some time. Do you need the microcontroller pin to have a different voltage than the transistor base (I assume when you said gate you mean base…gates are for FETs), or is this good enough?
Uh yes, pin to base.
I still couldn't come up with a way to make it work using a resistor-capacitor circuit, but I did learn a lot (that particular rabbit hole led to me an article discussing capacitance in potato tubers...!).
There is probably a better way of solving it, but at least I got it working with another transistor to "decouple" that sensitive pin from the base. I'm not exactly sure why there's a negative voltage across base and emitter, but it was preventing boot.
I'd be very interested in hearing any criticism you would be willing to share. I have hopes of moving this from my breadboard and solder it to a PCB so I can put it into a paper-cut lightbox that will be controllable from HomeAssistant, but I wouldn't want to risk setting anything on fire...
One thing that concerns me is that 7333A. I only have it in a TO-92 package, and while it's only powering the ESP-01S, which doesn't really draw that much current, it still gets uncomfortably hot to touch (I can hold it for a few seconds, but not much longer). Is there a better alternative, or is it supposed to get hot?
Thank you!
[edit: updated the circuit, I had misplace a resistor]
The 7333A is a linear regulator, which means it drops voltage by converting power to heat. Typically those make sense when the input voltage is close to the output voltage or the load is very small. If it’s getting too hot, the load is high enough that the efficiency will be very bad…whether or not this is a problem depends on your application.
Some random site claims 170mA and another claims up to 400mA. 170mA * 8.7V (12V in minus 3.3V out) = about 1.5 watts, which is too much for a TO-92 package.
Can you use a tiny buck converter instead? Or a larger package for the linear regulator that can add a small heat sink?
As for your actual circuit, the second transistor is an interesting idea (you’re using it to invert the state so you can have the GPIO pulled in the non-problematic direction?) and I don’t have enough experience to give further suggestions.