GSM shield, interruptions and sleeping code

Projects General Guidance
1

Hello,

I am building a system with UNO and a GSM shield. I am trying to make a system that runs on batteries, so it must consume as less power as possible.

I would like arduino to spend most of the time sleeping, and wake up whenever any of these two events take place:

  • 1 minute passed
  • a button is pressed

As far as I know, arduino can wake up from sleep by means of interruptions on pins 2 and 3, but GSM shield is using them. Can I also attach a button to those pins? Would it be possible to move the communication with GSM shield to other pins? My guess it's that GSM needs to use those pins for a certain reason which I don't know.

I'm aware that the first step to save power it's to replace the voltage regulator with a more efficient one, I will do that too :slight_smile:

Thanks in advance.

2

Can I also attach a button to those pins?

Not while the GSM shield is using them.

Would it be possible to move the communication with GSM shield to other pins?

Bend the pins so they don't fit in the slots. Solder wires to the pins, and to two other pins, and use the two other pins in the SoftwareSerial instance setup.

My guess it's that GSM needs to use those pins for a certain reason which I don't know.

Laziness.

None of this, though, will allow you to turn off the GSM shield. Without doing that, you won't save power.

3

Thanks for your comments.

Bend the pins so they don't fit in the slots. Solder wires to the pins, and to two other pins, and use the two other pins in the SoftwareSerial instance setup.

I will definitely do that :slight_smile:

My guess it's that GSM needs to use those pins for a certain reason which I don't know.
Laziness.

It wasn't clear for me if the communication with GSM shield needed those two pins and in particular, because it was making use of the interruptions. After reading this Arduino Playground - HomePage it's clearer :slight_smile:

None of this, though, will allow you to turn off the GSM shield. Without doing that, you won't save power.

It is not possible to turn off the GSM shield using the power mode related functions? I haven't studied the functions yet, but I was expecting to control the 5V pin directly with those functions.

4

but I was expecting to control the 5V pin directly with those functions.

Time to adjust your expectations, I think.

5

Bend the pins so they don't fit in the slots. Solder wires to the pins, and to two other pins, and use the two other pins in the SoftwareSerial instance setup.

I am quite confused on how to change the default pins to other pins in the arduino. The GSM library is the one which creates the SoftwareSerial. Diving into the code, in file GSM3SoftSerial.h I found this:

// An adaptation of NewSoftSerial for Modem Shields
// Assumes directly that Serial is attached to Pins 2 and 3, not inverse
// We are implementing it because NewSoftSerial does not deal correctly with floods
// of data

and GSM3SoftSerial.cpp

#if defined(__AVR_ATmega328P__) 
#define __TXPIN__ 3
#define __RXPIN__ 2
#define __RXINT__ 3
#elif defined(__AVR_ATmega2560__) || defined(__AVR_ATmega1280__)
#define __TXPIN__ 3
#define __RXPIN__ 10
#define __RXINT__ 4
#elif defined(__AVR_ATmega32U4__)
#define __TXPIN__ 3
#define __RXPIN__ 8
#define __RXINT__ 3
#endif

I think changing the values to i.e. 5 and 6 would make it. This might be a stupid question: the pin numbers specified must be always the ones of the arduino and not the shield, right?
If I modify the .cpp file, the IDE will be aware and will recompile it or should I do something special?

6

After trying it out, I will answer myself :slight_smile:

Modifying GSM3SoftSerial.cpp is enough. Arduino will recompile the library and use the specified pins. I love open software.