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?