RPi + Sipeed Tang Nano 20 k: new breakout board for LitexCNC

With the 5A-75B and 5A-75E we have a low cost way of creating a driver board for Linux-CNC. Based on the work of Romanetz, the project  LiteX-CNC  was started, providing a easy customizable firmware and driver to use these boards. The down-side however is that these boards require some soldering work to be done to accept inputs; I've messed up some boards in the process....

Therefore, Litex-CNC is going to be expanded to accept more FPGA's, starting with the Sipeed Tang Nano 20k. Compared with the 5A-75B it has less outputs (28 compared to 48 for the 5A-75B), but this is still enough for a simple 3 axis machine. The big advantage is that no SMT soldering skills are required to get this board up and running.

For the Raspberry-Pi I've designed a HAT, which provides:

• 7 extended PMOD-connectors. Each connector has 4 GPIO, power rails (+5V, max 200 mA) and a buffered enable signal;
• RS489 connector for communicating with for example a VFD;
• communication between Raspberry PI and FPGA using SPI in bidirectional mode (3-wire) to save on pins;
• conforms to the HAT+ specification , including a EEPROM with settings.

With the PMOD-connectors one can easily connect to break-out boards providing stepgen, GPIO (12V/24V inputs and outputs), differential encoders, etc. I'm also working to provide support for shifting data out (74HC595) and in (74HC165).

An estimation of the HAT will be around 7 Euro's, excluding the Tang Nano 20k. Inlcuding the FPGA, the price would be around the 40 Euro price point.