I need to make Raspberry Pi as my master and communicate with several slave devices (5-6 Attiny2313 in my case) that are kept 20-30 m (65-100 ft) away. Following are the requirements:
- cheap (preferably no external hardware)
- uses minimum number of wires (preferably two wires)
- speed can be very low.. it is not an issue... i just need to turn some devices on and off at the slave end.
- reliable over distances of 20-30 m (65-100 ft)
Please suggest me some communication protocol that can handle all these requirements.