This is project about DL3LAC's Antenna Tuner called "Christian-Koppler". The original tuner used an semidigital remote controller and 24line cable between the tuner unit and remote controller. I decided me to build the tuner unit and replaced the controller part by an ATmega MCU on both sides and linked them with cheap network cable. The used protocol between the controllers are RS422 based and is frame based with checksum. The tuner relays are switched each sepperate and the I/O unit are an two MCP23017 as I2C-Bus expanders.The MCU is an ATmega88 in a small housing. I decided me to use I2C-Bus Expanders instead using an ATmega 1284p and direct I/O handling in the expanding capability of this concept. If i need more I/O or and ADC, RTC, Temp-Sensor or ever, i need just 3 Lines to join the hardware extension to the bus.
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