... I have it on my arduino uno, and want to communicate with a 2nd arduino uno - to read and display the temperature that the 2nd one has measured, and to send it commands.
I don't see any specifics on this shield on how to do this - it has male pins labeled ICSP, and some unmarked holes that I can solder to on the digital pins side, but it's hard to tell what exact pins these are.
How can I communicate with a 2nd arduino? Should I be looking into wire.h and using the ICSP pins?
You could use hardware serial on pins D0 and D1, (unless you want to also print to the serial monitor), software serial on a couple of the other pins, I2C on pins A4, A5/SDA, SCL, or even SPI if you wanted. That's up to you, as long as you don't use pins that are already used by the shield. They're listed in the datasheet, (if you could call it that). The only LCD pin not listed is RS, (register select). It just says D*. Very poor documentation for a so-called "datasheet".
Serial is probably the easiest form of communications to set up.
Have you got the LCD working yet? If not, concentrate on that for starters, then worry about comms once the LCD is singing and dancing the way you want.
Edit: Looking at the LCD pin order, maybe RS is on pin D8.
Out of interest, did they supply you with header sockets to solder on for access to the unused pins? I notice that none are fitted in the datasheet photo.
Ho ho ho. "D*" is actually "D8" with the shift key held down.
I hope that the button marked "RST" is not actually connected to the Arduino reset. It looks too easy to hit that one by accident.
You definitely need another shield to stack under this and create a connection point for the Arduino-to-Arduino link. The Tx and Rx serial lines are easiest to use, although you may need to unplug when programming the Arduino. See Serial Input Basics - Updated for some ideas on how it might work.
Edit: wrong link - previously went to a discussion about Robin's thread, not the actual tutorial.
Cheers for the replies guys, and for clarifying what those pins are. Pretty useless "datasheet" hey?
I managed to get the LCD working no problems, but am problems with some of the buttons (based on code I got for a similar lcd+buttons shield). I think i'll need to figure out the button voltage levels by trial and error (button presses are input via A0 voltage levels)
Anyways, looks like serial I2C is the way to go as A4/A5 are available and I can solder directly to a hole that's provided. Thanks for pointing me in the right direction.
How far away is the other Arduino? I have had problems with I2C when extending it more than 10cm. Others on this board have claimed to run I2C a few metres.
TTL serial (just direct from the Arduino pins) can go 20m or more in a domestic environment. With the right converter chips, you can go kilometers.
