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I want to connect an Arduino Uno to an Arduino Nano, so that it can send signals. The problem is that the Arduino Uno has a motor shield connected to it, and it takes up all pins of the Arduino.

This is a picture of the whole motor shield contraption if it helps:

enter image description here

Does anybody know any solution for this?

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    Just because a shield sticks pins into the Arduino it doesn't follow that it uses all those pins. Read the shield schematic or manual to see what is actually used and what is not used. Chances are only a few pins are actually used.
    – Majenko
    Jul 15 at 18:56
  • Yeah, i figured that out, but its not really possible to keep only one side of it plugged in. Can i solder wires from the arduino to the pins that are not being used?
    – Julius
    Jul 15 at 20:05
  • Of course you can. Or you may find there are connections on the top that just connect direct to the Arduino pins.
    – Majenko
    Jul 15 at 20:43
  • On the image it looks like you can solder pin headers to the shield to connect the other pins from there. Though to say for sure we would need to have a look at the shields datasheet/product page. Can you provide a link for it?
    – chrisl
    Jul 15 at 20:55

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Pins 0 and 1 are serial pins which are also connected to usb, and you use them when you are programming your board or when you send anything to serial. It is unlikely that any shield uses it unless it has to and it although has a benefit of being able to listen to what the Arduino sends. I think hitching a ride on pins 1 and 0 (rx/tx) would be the easiest. SO you can print or write to them the same way as you respond to yourself.

Just a warning that when you are sending data between two boards and Print numbers they come as symbols of the numbers, not the numbers themselves So Serial.print(7) would arrive to the next arduino as number 55 or symbol '7'. If you are sending numbers between two arduinos you can use write Serial.write(7); which does not change data, but your serial monitor on a computer wont read it right, or you can send them as symbols, but then the arduino listening may have to convert number symbol to the number. (sooner or later you will have to create yourself a simple function to convert symbols to numbers in your project...

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