Tinysine SIM900 GSM shield - where is DTR?

When using transparent data mode there are 2 ways of returning to command mode

  1. Software - sending the string "+++"
  2. Hardware - set DTR high.

I know how to do the Software way, now I want to try the Hardware way. The only trouble is how to connect to DTR.

If anyone has access to the schematics for this shield - please share. After many hours of searching I'va had no luck.

The shield has an unpopulated GPIO but no hint what they are used for - anyone know?

I think the attached is part of the schematic for your shield.

Tiny OS GSMSHIELD-1.pdf (44.7 KB)

Thanks for the help. It shows a bit of info. Sadly DTR is disconnected and I don't trust my soldering skills to connect a wire myself.
Where did you find it? Maybe there's more there.

I've had the file for some time so unfortunately I don't know where I got it from.

Hi,

I use the DTR on my SIM900. I use a custom made interface board to interface the MEGA2560 and the SIM900. In place of the interface board, You can use a small jumper to an unused pin of the MEGA2560 and control the DTR with that. Any questions, please reply.

Stan K