Problems stacking Arduino Shields

Question

I'm trying to stack the Adafruit Data Logger Shield https://learn.adafruit.com/adafruit-data-logger-shield/overview onto a CuteDigi Sim900 GPRS Shield so that I can upload data (collected eventually by a GPS breakout) to a server at certain intervals.

The problem is that I can't seem to get the two shields to play nicely together. I'm a beginner with the Arduino and electronics in general, so hopefully this is just a noob issue.

When I power on the GPRS Shield, the data logger stops outputting the Date/Time to the serial monitor. And when I turn the GPRS Shield off, the serial monitor continues again and shows the Date/Time from the data logger.

They don't share any pins that I'm aware of, and I've tried connecting a 7.4V li-po for external power with no success.

Any help is greatly appreciated!

Answer 1

Make sure you are using a software serial port for the GPRS shield.

If you aren't using the software serial port, then you are probably running into an issue with trying to read data over the only UART (serial) port while two devices are tryiing to use it.

It looks like there are two jumpers next to D0/D1 on the GPRS shield, I can't tell but I think if you remove those, the shield will use software serial over D7/D8. If you do this, you'll have to code your program to use a software serial. This wiki page on the GPRS shield if you need help with that.