Odd Sound Behaviours With Bluetooth Module BT-909

Proffieboards
21

A 33k pullup shouldn’t really have an effect, since it’s pretty weak.
Of course, there could be a short or something which would be a different matter entirely.

22

If there is a short I can’t see one.
Maybe at BT where i soldered the switch on, but I don’t see it.
Here are a few pics:
Board from above

proffie0-2048
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“LED6”-side

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“LED1”-side with CAPs

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BT909 from above (through battery slot)

proffie3-2048
proffie3-20481536×2048 381 KB

BT909 from the side with switch

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Maybe, because the switch can move a bit, its metal casing could sometimes touch the smaller Cap. Not sure though.

Could this cause a short?

23

I don’t think the metal of the switch should connect to anything, but it depends on the switch.
As for “not seeing a short”, I would like to quote Obi-Wan: Don’t trust your eyes, they may deceive you. But instead of using the force, I suggest using a multimeter to check for shorts.

24

So I went and did a re-do of the soldering on the PCB side of the bluetooth module.
While I was at it, I soldered it to SD Power to test the behaviour without 33k pullup and extra CAPs.

It kind of worked. I didn’t get a boot sound and this time around, this stayed true even when I re-plugged the battery shortly after unplugging it. All other sounds were working from what I could tell.

Eventually I ended up soldering it back to 3.3V between 33k pullup and my two CAPs. I just improved on the soldering on the PCB and wired in a new switch which I took further away from the capacitors so it wouldn’t accidently connect when switching around.

Going to double check with a multimeter tonight. I measured something between BT 3.3V and BT GND, but I guess this is to be expected, because of the two capacitors on the PCB bridging there.
image

I was of course checking this during my initial wiring, but it can’t hurt to check.
Any particular area I should especially focus on? BT only or everything?

25

I think we were mostly curious about shorts between the 3.3v and anything nearby, as that is primarily what would cause stability issues on the 3.3v supply.

26

Here are some values:
3.3v - D1: 32.9k
3.3v - SD Power: 41.1k
3.3v - GND: 51.1k (two capacitors are bridging these)

I also get values between 3.3v and

  • SDA, SCL
  • Batt+
  • GND, Batt-
  • TX, RX

Unfortunately I can’t decipher which is normal and which shouldn’t be there.

27

This looks normal to me.
Shorts would be low values, like less than 1000 ohm.

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