Arduino Pro Softserial Not Functioning?

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Hello, I do not know if this belongs in this forum or another but I believe it is a microcontroller issue.

I am trying to integrate an Arduino Pro (full-size or mini 3.3v or 5v) with a Linksprite SIM900 shield. We are using the provided Linksprite test code found on this page (SIM900 GPRS/GSM Shield - LinkSprite Playgound).

What works:
We have been successful with this code on an Arduino Uno and a SainSmart Uno sending text messages with the Uno powered by USB and the SIM900 shield powered by an external 4.8-5.2v power source. On the SainSmart Uno there is a 3.3v / 5v switch. The code works on both. In this case, we type a letter into the serial monitor which sends AT commands to the shield and responses are shown on the serial monitor.

What doesn't work (but we want it to):
When we connect the an Arduino Pro (3.3v) or Arduino Pro Mini (5v) to the shield and power the Arduino by an FTDI Friend or FTDI cable and power the SIM900 shield by an external 4.8-5.2v power source (same code as above). In this case the serial monitor is unresponsive. To confirm function we have configured a circuit to read and display analog sensor readings on the serial monitor, this was successful. My suspicion is there is something up with "softserial" but I am novice to Arduino so this is a mere hunch.

Has anyone else had a similar issue or have any pointers for us? As we intend to run our system off batteries we do not want to use the standard UNO as the regulators draw significant current not doing anything.

Thank you in advance for your help and I look forward to your responses. Cheers!

-Aaron

Bump... 42 views and not one reply!

They all use the ATmega328(p) or ATmega168 chip. If that works with one board, it should work with another board also.

The difference is the crystal (8MHz or 16MHz) and the voltage (3.3V or 5V) and pin 0,1,13 and some Arduino boards have other input logic voltage levels.
Pin 0 and 1 are used for the serial connection with the PC via the usb.
Pin 13 is for the system led. Sometimes a gate is used, sometimes a resistor with led is connected.

You should use the newest Arduino (version 1.0.5 at the moment), and the SoftwareSerial that is included in 1.0.5.

I can't figure out the SIM900 shield. It uses 5V and the logic is 2.8V ?
The 2.8V is not enough for a 5V Arduino board.

The 8MHz clock might cause an inaccuracy of the baudrate.

The SaintSmart at 3.3V still runs at 16MHz, even if that is out of specs.

Can you do this test:
Use an Arduino Uno for the 3.3V to power the Arduino Pro.
Be sure to connect all the grounds, the GND of the Arduino Pro, the Arduino Uno and the SIM900 shield.
Use different pins for the RX and TX, pin 7 and 8 might be damaged while trying to make it work.

Hi,
Did you manage to solve the problem. Currently I am using Arduino Pro Mini and SIM900 shield. With the Arduino Uno everything works fine. I can make/receive a call, also send/receive a message. But with the Arduino Pro Mini nothing happens. The serial monitor is unresponsive...
Cheers.

rogatip:
Hi,
Did you manage to solve the problem. Currently I am using Arduino Pro Mini and SIM900 shield. With the Arduino Uno everything works fine. I can make/receive a call, also send/receive a message. But with the Arduino Pro Mini nothing happens. The serial monitor is unresponsive...
Cheers.

So I've manage to solve it. The tricky part here is in addition to connect RX and TX, the GND also should be connected between the Arduino Pro Mini and the GSM shield.