New sibling project: HUB75HAT

[Peter-van-Tol]

In topic Raspberry Pi + SPI there have been some images for the development of a HAT for the 5A-75B. Last Saturday I've launched this open-source project in The Netherlands during a CNC Tech Meetup, so I opened the repository. You can find it here.

The board features:

• Designed for Raspberry Pi 4 and 5 (the older version RPi 3 might also work) with SPI communication
• 3 I/O connectors:
  • each 17 pins of freely addressable inputs / outputs;
  • selectable 10 kOhm pull-down or pull-up resistor;
  • optional 5V power supply on the connector;
• 2 RS489 connectors for communication with VFD's or other peripherals (powered by Rasberry Pi);
• number of GPIO can be extended by using serial connection through the three I/O connectors (up to 64 GPIO per serial channel);
• eco-system of break-out boards designed for the HUB75HAT is under development. Currently the following boards are available:
  • BOB4STEPGEN: 4 differential stepgen drivers with ENA, DIR, PULSE outputs and ALARM input. The board also has 4 inputs for homing switches, which can be individually selected to be either NPN or PNP.
  • BOB4ENCODER: 4 differential encoders with A, B and Z (index) channels. Per channel it can be selected whether it is differential or single ended, allowing re-use of possible unused channels. This board also features connectors for serial daughter boards for expanding GPIO or attaching other sensors.

Total cost of building the HAT (excluding the Raspberry Pi, but including the 5A-75B) is around 35 Euro.

There is still some work to do in that repo, for example the board has the following issues:

• the space around the 40 pin connector of the HAT is a bit tight with the mounting points of the RPi. The solution to work with the current board is to use plastic stand-offs and cut part of these away.
• the enable signal should be inverted on the board, because the buffer Output Enable (OE) is active LOW. I rather send a HIGH signal to the board to enable it (safety).
• enable LED is not working (can also be a problem with the buffer IC, had some trouble with soldering this buffer). However, even if this LED was working, it would indicate that the board would be disabled (see previous point);
• The 3 I/O headers do not have space for shrouded headers. In stead, I chose to use coloured pin headers to show the different functions of the pins;