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Tips and questions relating to the GPS modules from SFE
By jtjj222

I am using a Sparkfun GPS shield and MP3 shield together in a project. Independently, both work perfectly. When stacked onto each other (gps shield at the top), the GPS shield only works when there is no music playing.

The MP3 shield uses pins 2 and 3, so I cut them on the GPS shield and put some electrical tape just to be sure. I used jumper wire to connect pins 2 and 3 on the shield to pins A0 and A1. The GPS still functions perfectly, except when music is playing. Using pins 5 and 10 for Rx/Tx causes the same problem.

When music is playing, the frequency of the updates that I get from the gps decreases and I get garbage data. If I call MP3player.stopTrack(), immediately the GPS begins returning sensible data.

Picture of the setup: ... 037997.jpg

Any help would be greatly appreciated. Thanks!
By Valen
There was no need to cut the lines on the GPS shield. If the switch was set to the UART position, instead of DLINE, then D2 and D3 pins from the Arduino would not be connected to the GPS module. (And free for the MP3 Module) Though any data sent from the PC/serial monitor would conflict with it. How did you have this switch set?

According to the MP3 shield hookup guide there are different board versions. Which one do you have?

You haven't shown any code of this program you have running. It's probably a software issue, or a timing issue: SPI processing of the MP3 player conflicting with UART processing of the GPS.