Hi Greg!
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I have read that portion of the manual too, since I bought QMX+ to integrate the ATU tuner and internal battery. And, as an experimenter, mentally I was ready to accept risks associated and bite the bullet.
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So, I did not think that Nano would cause an appreciable current to be drawn while radio is off and it is powered through the usb.
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Without turning radio off and arduino being powered from QMX+ - all has been working perfectly for couple of weeks. Until I plugged usb to arduino and turned radio off :)?
And, I did that on purpose to see the serial debug messages from my code while radio is powering up.
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And before powering arduino from QMX+ and USB on it - it also consistently worked from the protype board and arduino being powered with its own power supply. But grounds between itself and QMX+ were shared. Turning radio on/off did not cause any issue. So, these two bits of a success deceived me :)
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I have a revision 2 board with SMPS integrated. But most of its components are big enough I can resolder them with my fat fingers. Now I will have to troubleshoot to find what is broken on SMPS. Will follow Steve's advise.
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73,
Sardar ( AC8L).
