APC220 radio

231005 - code here might be outdated

The APC220 radios is one of the simplest ways to implement radio communication between computer devices.

The APC220 has a simple serial transmit receive interface.

You dont have do do anything but just connect your rx and tx on your microcontroller to tx and rx on the radio.

setup

   micro TX --> RX(APC220)  ---radiolink---> (APC220)TX -->  RX(another micro)

Transmission - Half duplex

The APC220 use the same frequency both ways aka half duplex.

So you are responsible for only one unit at time transmitting.

A messy network

The APC220s can send and receiver from another identical device. So ther is no problem having 2,3,4,5… 'nodes’ in your setup.

Your (or your sw) will be responsible for handling communication.

Could be

• One master node, many slaves (like I2C)

• Token based system (like arcnet)

• Your own idea.

Ther might be issues about timeout bq if you only transmit a few bytes then the APC200 wilol first wait a little bit until it finally ship the short package.

NB; I have not been able to find documentation so this is learned by playing :-)

Robust radiolink

The APC 220 radio byte stream is encoded and have added forward error correction so there is a high chance that your data will be received without any errors.

This has a cost in capacity. So if your transmit 100 bytes the APC2200 will transmit 180-210 bytes in the air. This overhead must be taken into account in your link capacity budget. A conservative rule of thumb is to multiply with 1.0 or 2.0 to the bytes that are going to be transmitted.

This apc220 interface and configuration library is based on a simple C class

It is based on use of SoftwareSerial so on a UNO the hardware serial port is available or other things.

On a cansat it could be like

• hardware serial for logging data on sdcard

  • higher baudrate than for radio to log large amount of data

  • 57600 which gives 5000 bytes to log pr second

• software serial for telemetri back to your homebase

  • 9600 baud or lower (lower for extending range)

  • a few hundred bytes pr second

Still beware of your databudgets. Dont use all CPU power and time for logging

If you have a MEGA there is 4 hardware serial ports. In that case you can just change the serial port library to just use a hardware serial port.

because …

Changing frequency on radio

The library provide a simple interface for reprogram the apc220

See examples

See apc220code.html

more to come

Jens

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