I actually have this problem with my SD Card reader too. I have an external power supply, (A 5V, 2A tablet charger) to the SD CCar reader and my GSM Board. I can solve the problem with the SD Card by using a transistor to feed the charger voltage into the SD Card reader when the arduino is powered on. However, this does not work for the GSM Board. The GSM board wants to be connected to Arduino ground before it will turn on when powered via transistor. So I connect eh 5V directly to the board, and GND to GSM GND, and it will turn on. Great, right? Well, the problem arises when I want to use the board. Using the AT commands, I get an output of "ÿ". The baud rates work for both Serial objects so Serial isn't the problem. Then, I tried fixing this by connecting everything to the external power. Power the arduino, gsm and SD Card Reader all by the charger. (By external I mean non-computer USB) However, the GSM will then only send and SMS every so often, seemingly random at times. It will output to Serial that it sent, and light up the LED that it is sending, and consequently sent, but I will never get the message
- Arduino, GSM Board and SD Card do not communicate well, if at all, on separate power sources
- GSM Board does not want to work on external power with transistor to control on/off with arduino
- GSM, Arduino on same external power, GSM not always sending SMS though tells Arduino it did.
Arduino: Arduino Uno R3 GSM Board: SIM800L EVB V2.0 SD: MicroSD; Brand unknown. Came with a 3D printer Power Requirements: 5V, maximum 2A