Hi recently I've could send some messages with the A6 GSM module, which uses AT commands. To switch on the board, you need to press the power button about 4 seconds or connecting the VCC pin to the PWR pin to avoid manual switching on. In this Andreas Spiess' video (minute 2:21), he recommends reset the device to give to the board a defined state. I had not done this until the device didn't work properly with some scripts. To reset it, he advises to reset the modoule. Its RST pin needs 0.70 mA and works at low level. In addition, the Arduino can not provide that current with a single pin so he uses a N-channel MOSFET (3055) to reset the board.

In my case I used a transistor (I don't know if it's NPN or PNP) and I connected the circuit like in his video. It worked! But it given strange results to the serial monitor (yes, I set the baud rate correctly). After reset the board it switched on automatically because it was connected the PWR pin and VCC pin. The mistery occured when I unplugged the board (even its current) and then I reconnected it again. Since that moment it doesn't work, it doesn't switch on its LED to show you that the board is working. So, can anyone explain me why the 3055 it's neccesary to reset the board? Can it be done using Ohm's Law, a digital pin and a big resistance to give to the board the 70 mA?

Thanks!

  • try use program "at command tester" with ftdi for example, it works in my case but the the free license only works to 30 days. – Diogo Cid Feb 14 '17 at 22:36
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    Its RST pin needs 0.70 mA and works at low level. It is 0.70 mA or 70 mA as you mention later on? – Nick Gammon Aug 12 '17 at 22:12

I come across this problem too..based on what you said, i think it works like this:

The parameter you are looking for is power rating.. Arduino digital pin can only tolerate some amount of current, and im guessing it is less than 70mA..if you still do that, it is possible to damage that pin..since you want a LOW level for trigger, you can connect that RST manually to GND.. GND is also 0V just like the DIGITAL LOW, but it has no internal circuitry as of digital pin - meaning that you can sink a lot more current to GND.. If you want to be on the safe side, connect a limiting resistor(use ohm law for value), and also take note on the resistor power rating..

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