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I noticed that the pinout for cheap Baofeng connectors has +V available. I'm interested in powering some electronics directly from this connector.

When unloaded, this seems to have about 3.3V on it, but when I try to power my load (an ESP32), the voltage drops to 0.8V.

How much current can this pin actually provide without significant voltage drop? Or, what does the voltage/current curve look like?

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    $\begingroup$ Have you measured the current draw of your ESP32 to rule out a fault? $\endgroup$
    – Phil Frost - W8II
    Commented May 29, 2019 at 17:42
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    $\begingroup$ The voltage is probably meant to bias an electret microphone, so I wouldn't be surprised to hear that that terminal can't source much current. $\endgroup$
    – rclocher3
    Commented May 29, 2019 at 19:48
  • $\begingroup$ 3.3v is a common level for logic signals in electronics. This page linked in the other question seems to indicate V+ can be used for PTT 2 - is that not the case? $\endgroup$
    – JPhi1618
    Commented May 30, 2019 at 18:16

2 Answers 2

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  • With no load, I measure 3.17V
  • With 100kΩ load, 2.91V
  • With 10kΩ load, 1.59V
  • With 1kΩ load, 0.29V

The math works out to a 10kΩ series resistance between +V and ground.

As such the maximum power that can be drawn is at 1.59V/10kΩ load, or 0.25mW max power. Short circuit current would be about 0.3mA.

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I would first measure the current draw of your ESP32 to rule out a fault there.

The +V pin on the Baofeng microphone connection is probably intended to bias an electret microphone. These are essentially a capacitor, with sound pressure changing the spacing between the plates and thus the voltage. They contain a FET buffer since the capacitor could not drive a cable directly. The buffer requires power, but very little: the bias current is probably far less than 1 mA.

Thus it's quite likely the +V pin is unable to supply even a small current. Adding a series resistance on such a pin would have no impact to the intended use of biasing a microphone, but is a cheap and effective way to protect the radio from all kinds of faults that could happen on such a connector.

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    $\begingroup$ Almost certainly an electret mic. The only other possibility would be for the PTT; pressing it might feed 3.3 volts back to the main board. $\endgroup$
    – Mike Waters
    Commented May 30, 2019 at 15:39

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