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Topic: Arduino Mega & GSM TC35 shield - connection lost when wiring (Read 528 times) previous topic - next topic


Dear all,

I'm new here and hope, someone might help me. I went already through a lot of forums and googled for hours, but I can't solve my problem.

I'm using an Arduino Mega and a Sunfounder GSM TC35 board (and a RTC, but this doesn't matter). This is exactly what I'm doing:

  • Wiring Mega with +5V (max. 2,5 A) external power supply
  • same with the GSM board
  • switching power on
  • pressing toggle on GSM board to connect to GSM - connected after some seconds as stated by the flashing connection led (short flash ever 3 seconds).
  • Now connecting the GSM to the Mega (the Software Serial library is using Pins 2 and 3 with an Uno but 10 and 3 with a Mega
  • On the GSM board I'm using the TXD0- and RXD0 pins. Many sources are saying that on this board, TX and RX are labeled wrong. So I'm connecting Pin 10 of the Mega (Uno = 2) with TXD0 of the GSM and 3 with RXDO.
  • The serial monitor is showing that the sketch is still waiting for the GSM connect, even when the connection is already up.
  • Much more anoing than the not running sketch is, that roughly after 10 seconds I did the wiring between Mega and GSM, the connection led of the GSM is showing that GSM connection is lost. It will stay like this up I unwired TXD0 and RXD0. Without the wiring between Mega and GSM the connection will be up again.

I hope, someone will come up with a great idea.

Thanks in advance from a very frustrated German guy...


solved by adding a wire between ground of both devices.

On the other hand it seems RX <--> TX and TX <--> must be connected (and not the otherway round as said at many sources...)

Now I'll open a new post with my second problem.

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