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I have an Arduino GSM Shield mounted on an Arduino Uno. Can I stack this GPS shield above Arduino GSM shield? Will there be any pin configuration problem?

In GSM Shield hardware pin’s configuraton are as below:

0 - Not connected
1 - Not connected
2 - GSM Rx
3 - GSM Tx
7 - Modem reset

If there is any problem, how can it be solved? I would be happy if there are any alternatives for the GPS shield.

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Start by finding the circuit diagrams of both shields and lining them in your question. –  jippie May 4 at 9:51
    
According to the GPS shield quick start guide (sparkfun.com/tutorials/173), it seems possible to select different pins for serial communication than the default ones (2 & 3) that conflict with yout GSM shield. So that should be OK. –  jfpoilpret May 4 at 11:15

2 Answers 2

enter image description here
Photo by John Boxall

Which pins do they use?

To determine if two shields are compatible, you have to read the specifications of both shields.

The best source for this information is the data sheets supplied with the shields. However there is also this Shield List

Can you reassign pins?

Some shields provide a means to alter which pins are used for communications. This can take the form of a switch or a jumper - either pull-off or solder-bridge type. (the GPS shield in the question has jumpers).

Where the shields do not support pin-reassignment or provides insufficient flexibility, to work-around incompatibilities you can use an in-between shield designed for the purpose.

here is one example:

You hear it all the time in the Arduino community, “will this shield work with my other shield?.” I think we’ve all been disappointed to find that two of our favorite shields compete for control of a digital pin here or a serial pin there. While there are sometimes some clever workarounds from elegant code modifications to aggressive ‘greenwiring,’ Mayhew Labs may have come up with the simplest solution thus far: The Go-Between Shield.

Are any alternatives for the foo shield

I notice that Arduino.cc now point people to the list referenced above. They used to have their own list.

Product recommendations are off-topic here but, obviously, you can search

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+1 for the link to Arduino shields references, and for the go-between shield as a generic solution to this kind of issue. However, in this specific case, a go-between shield seems useless as the GPS shield allows changing the TX/RX pins (2 & 3 are just the default pins) quite simply. –  jfpoilpret May 4 at 11:46
    
@jfpoilpret: Good point. I'll update answer. –  RedGrittyBrick May 4 at 15:19

From the shield description, the TX and RX of the GPS are mapped on pins 2 & 3, like your GSM, so you'll have to change that.

I'm using Adafruit GPS + flash card shield, which is a bit cheaper (and uses pins 7&8).

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But my GSM shield uses pin 7 uses modem reset. Will It create any problems by placing GPS shield on the GSM shield ? –  Manihatty May 4 at 13:15
    
Yes, very same thing. Depending on what you want to do, why not use a breakout plugged on a breadboard ? You'll be able to choose pin assignment. –  Victor von Cacahuete May 4 at 15:34

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