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I’ve got a small Bluetooth module, it is powered by 12v and has 5 buttons on the side. I’ve desoldered and removed a few of them with the intent of triggering them programmatically via another device.

When I connect these two terminals together briefly the relevant action is triggered (in this case, it skips to the next song on the connected bluetooth device).

bluetooth module with wires soldered

Multimeter says there is 3.4v when measured from the white wire to the red one.

I used a transistor (2N2222) to create a gate that my Arduino can open (white to collector, red to emitter, Arduino GPIO to base) but it’s not triggering the action (same setup seems to work fine with a simple LED).

Can anyone clear this up for me?

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    \$\begingroup\$ Is Arduino ground also connected to emitter? Is there a base resistor? \$\endgroup\$
    – Justme
    Commented Mar 8, 2022 at 14:49
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    \$\begingroup\$ It might be simpler to use a relay controlled by your Arduino in place of the switch. \$\endgroup\$
    – jwh20
    Commented Mar 8, 2022 at 15:02
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    \$\begingroup\$ Vce of the transistor might be to high to be considered low. Maybe you need to use a logic level MOSFET instead of the BJT. \$\endgroup\$
    – Arsenal
    Commented Mar 8, 2022 at 15:05
  • \$\begingroup\$ @Justme No, I hadn’t connected the Arduino ground. Just tried it at your suggestion and it works! (I’m not sure where I should add a resistor to the mix though) \$\endgroup\$
    – kevin
    Commented Mar 8, 2022 at 15:53
  • \$\begingroup\$ @Arsenal I will look into the Vice, got a box of various transistors here so maybe another one will be better for this \$\endgroup\$
    – kevin
    Commented Mar 8, 2022 at 15:54

2 Answers 2

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The reason it does (did) not work is that the grounds are (were) not connected. The current must flow from Arduino IO pin to transistor base and from emitter back to Arduino ground.

Also without any resistor on transistor base means that too much current may flow and it might damage the Arduino or transistor. There are plenty of tutorials how to drive transistors if you just do a search.

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Transistor has a voltage in ON state from emitter to collector, in 2N2222 goes from 0.3 to 1V. It could be that it doesn't get to the low level threshold required in your bluetooth module. Try using a small relay switch, which does not have this issue.

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