MOD-GSM-EDGE comms voltage

[aquarat]

Hi

Can I use 5V levels to communication with the MOD-GSM-EDGE module ?

I've been using 5V levels so far, but the module I was testing with stopped responding after a while... and now won't communicate at all via the serial link (even though the baud rate has been set).

There's no mention in the datasheet or manual that Olimex provides regarding voltage levels, so as a precaution I'm using a level shifter with my second module.

Thanks

[aquarat]

My second module has now stopped responding and this is while using a level shifter to bring the comms voltage down to 3.3v. The module is being powered from USB.

[dave-at-axon]

They have 1K series with 10K to ground to act as a potential divider on the input lines to the device. With 5V you would be putting 4.5V into the SIM700D. With 3.3V you would be putting 3V.

http://wm.sim.com/producten.aspx?id=1017

The datasheet says 2.8 to 3.0V on these pins to very likely that you killed it with 4.45.

http://wm.sim.com/upfile/201056144248.pdf


PS.. You will need to register with SIMCOM to download the files I linked to.

[dave-at-axon]

If you are connecting USB and UART you may be getting a conflict with the device internally.

Can you power it up from the 12V input as a test?

[aquarat]

Thanks Dave - a potentially expensive mistake on my part.

It's quite strange, at both 3.3v and 5v the modules worked for a fair period of time, enough to authenticate with a PIN, establish TCP tunnels and transmit data several times (over four hours).

[dave-at-axon]

Yeah, they will in most cases but after a while they will fail.

Try testing with USB on a computer as they should still be working even if the UART is fried.

I always use level shifters with the modems from SIMCOM just to be on the safe side.


AND ONCE AGAIN, the Olimex docs should have this information in nice big BOLD LETTERS in the docs but they don't.

[aquarat]

If you are connecting USB and UART you may be getting a conflict with the device internally.

Can you power it up from the 12V input as a test?

I connected to USB cable to a "dumb" power source and both modules are responding again . Thanks Dave!

This would probably also be the cause of all the auto-bauding related issues I had.

[dave-at-axon]

Good stuff. Glad to hear you got them both working again. That will save you the expense of going for a new module.