Radio battery saving

[payano]

The nrf24 radio consumes around 15mA when in RX mode.
The stm32f103 circuit can be set to sleep mode and draw around 2uA.

If a battery has 2000mAh and the only consumer is the radio, it can drive the radio for around 133,3 hours.

Because of the battery consumption from the radio, there might be a good idea to have three nodes in the network:

• Master
• End device
• Router

The master is directly connected to a computer and gets its energy from there. A router is connected to the main lines and can have the radio in RX mode all the time. An End Device is a device that uses a battery is energy source, therefore its good to set that radio in sleep mode as much as possible.