DCC Lift decoder

Decoder to control an elevator (lift) for model trains. The print includes two micro controllers. The ATMEGA 328 is used to control two stepper motor drivers (X and Y = left and right). Software is intended to be [GRBL](https://github.com/gnea/grbl/wiki). Limit switches can be connected via two [opto-couplers](https://github.com/gnea/grbl/wiki/Wiring-Limit-Switches). The ATMEGA 2560 is the main processor that: - Sends commands to the GRBL ATMEGA 328 - Receives [DCC](https://en.wikipedia.org/wiki/Digital_Command_Control) commands from a DCC master station - Sends feedback messages via the [RS-Bus](https://sites.google.com/site/dcctrains/rs-bus-feed) to the master station - Has 14 digital inputs for buttons and/or IR receivers (light barriers) - Has 14 digital outputs for LEDs and/or IR transmitters (light barriers) To offload the ATMEGA 2560, the software can be split over multiple PCBs. Communication between the PCBs takes place via a RS485 bus. Only 1 of the PCBs need to receive external power (AC 12-18V), the others may receive power from the main PCB. Costs for 5 PCBs with all SMD components assembled is around 100 Euro (including tax and shipping). Costs do not include the Through-hole components, such as jumpers and terminals. - Updated 2020/07/14: PAD spacing SS34 reduced