MDBT42 crashes with motor powered by its battery

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AkosLukacs in reply to @user111953

The Vin pin of the MDBT42Q breakout goes to a regulator, and that regulator drops some voltage (don't want to look up right now, but probably couple hundred millivolts). If you use a battery (for example the CR2032) that's less than 3.6V, connect it to the 3.3 pin.

And not exactly what you asked, but a motor - I assume it's running not only for milliseconds - even at 10-20mA is huge for a CR2023.
You should try somewhat bigger battery. Watch out for it's voltage! If it's below 3.6V, connect to the 3.3 pin, if it's over that, connect to the Vin pin. For example, Li-ion, Li-poly must be connected to the Vin pin. LiFePo4, CR123A can be connected to the 3.3 pin.

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user111953 in reply to @AkosLukacs

Thanks Akos !

I connected battery to the 3.3 pin and it seems to be better indeed, 100uF capacitors is now enough to prevent crashing.

Any idea to improve this ? And why the puck doesn't have this issue ?

And yes you are right about the CR2032 max drain. Actually it drains 10-20mA just during 2 seconds and a very very few times. I will change battery to a special one allowing high drain but first I really would like to make the MDBT42 as stable as the Puck. I need the circuit to hold as much as possible with end-of-life batteries.

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Robin in reply to @user111953

Sat 2021.05.15

re post #4: 'And why the puck doesn't have this issue ?'

Likely the regulator U2 MCP1703T

See schematic link below heading 'Information'

http://www.espruino.com/MDBT42Q

See schematic ('Circuit Diagram') link(s) below heading 'Information'

http://www.espruino.com/Puck.js
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AkosLukacs in reply to @user111953

That's better. I can only guess, but you are abusing that poor CR2032 battery, a couple of things come to my mind:
Battery itself. Do you test with the same battery? Or at least same brand, same state of charge? Might be simply the one with the MDBT42 breakout has less capacity, higher internal resistance, etc. Check the no-load battery voltage at least.
Battery holder and leads: Lead length can affect resistance and inductance. Might be enough for different behavior. Lead length from battery to the uC in case of the Puck is minimal, in case of the MDBT breakout I guess it's longer.

Do you have an oscilloscope to check voltages? Or if you don't have anything better, just sampling the voltage with any uC might help to get more info...

Edit: a capacitor with smaller voltage rating, that would be physically smaller. And maybe even a low-ESR small-ish capacity one could help...

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