GPRS Module unexpected reset

I´m working with this cellular radio module:

(It it a SIMCOM SIM900)

Plugged on a Spyder board.

Here is the deal. If I turn on the GPRS gadget, after about 20 seconds without using it or send an instruction, the Spyder board gets a hardware reset.
After several tests I’m pretty sure that the SIM900 has a watchdog.

If this module indeed has a watchdog, how can I disable it?
If it hasn’t, what is making the SIM resets?

In addition, this is the power supply:

(USB client DP module)

What are you plugging in to the power supply, and how much power (amperage) does it supply? Do you have any other modules plugged in?

I’ve found that certain modules seem to have pretty high power requirements, and so if my input power is at all sketchy, the board may reset.

Since you are using the USBClientDP module, could you attach external power to it as well as USB, and see if that fixes your problem?

Thanks for your reply.
At this moment, the Spyder board has plugged-in the cellular radio and a T35 display. I can’t get the power requirements of these modules, but the power supply is able to give 800mA.
I suppose that the power supply was made for these modules. In the other hand, the USB client DP module has a component called “IC7” that works really hot.

Thank both of you for your help.

After made a lot of tests, i get to the conclusion that my problem is the GPRS’s power supply.


The GPRS module has 2 leds, D1 and D2. While D2 is blinking, everything seems to be fine. When D2 changes the blink frequency, come the problems. No matter how many modules are connected on the Spyder board, the cellular radio will reset itself.
I suppose that when D2 starts to blink slowly, the GPRS module gets signal. This situation must cause a rise of the current. If the .22 F capacitor is still charging, it will not supply to the module and the voltage will decrease.
In my opinion this is what causes the “unexpected reset”.

The cellular radio that we bought, don’t have an option for external supply. Maybe, I have to weld a connector.

Personally, unless you have a reputable brand plug-pack power supply and you know it maintains voltage up towards the 800mA upper limit, then I would be aiming for one with a few more mA (1A at least for all those things you have). If you want to try it out, take off the display as they suck a fair bit of juice, and it might make the GPRS device stable. That then definetely points to the need for more power - you may find you don’t need to to anything more than give the DP module more current capability from a new plug pack and you won’t have an issue and you won’t need to go soldering bits on.

One of the test i did, was take out all of the gadgets except of the GPRS. No matter how many modules are plugged, when the modem connects, it will reset itself.
The only way to pass this state is waiting about 15 minutes until power-on the cellular radio. But I can’t even think in sleep my program 15 minutes, while charging the capacitor, because I have to restore the connection.

Following your recommendation, I replaced the DP module installing a 500 W PC source. The GPRS module still resets the entire circuit.
I’m sure that the problem is the GPRS module and install a secondary supply or replace the DP module is not helping.

I would like to solve this problem asap please.

What voltage and what amperage you have added?

I recommend 12V at 1A, or better 2A.

3.3V 10A

Are you suggesting to supply the Spider board with 12V?
Maybe I misunderstood your answer.

Please see what voltages are listed under the connector.

Ok. I have already tried to power the circuit using the USB Client Module as dual power. In that case the circuit was more unstable than without the secondary power supply, even in release mode when is supplied by a single source.
The test I did today was disconnect the DP module and supply the circuit with the PC source.

Then we are back to our original question :slight_smile: What voltage/amperage you are using to power your board?

1° Test:
The secondary supply for DP module delivers 12V 1.2A.
2° Test:
The PC power source, supplies 3.3V 10A and 5V 7A.

I’m thinking that the power supply is not the problem. There must be something wrong in the GPRS power-on sequence.
Generate a power-on pulse and wait, is all that I can do.

It can´t be possible, I can´t be the only one with this problem.

Please give us steps to see the same behavior on our end.

This program initialize the GPRS module with no problems

    void ProgramStarted()


but this restarts before finish the power-on sequence.

    void ProgramStarted()
        while (true)

The board has connected the cellular radio in socket 4, socket 6 is unused.

[quote]void ProgramStarted()
while (true)

You can NOT put while loop in ProgramStarted(). See the comments generated by the designer.