Does it absolutely have to use tone detection? I think it would be far easier to get working reliably if you just added a pair of RF24 transceivers to your solution so that the two Arduinos could communication wirelessly.
Does it absolutely have to use tone detection? I think it would be far easier to get working reliably if you just added a pair of RF24 transceivers to your solution so that the two Arduinos could communication wirelessly.