Now that I have a chassis that can walk a little bit, I need to get the onboard computer working.  To do that, I needed to update the raspberry pi 3 daughterboard I built for the previous turret for the new bus voltage and communication format.

The rpi3’s UART is incapable of controlling the direction line on the RS485 transceiver, so I added a small STM32 micro in line to control the transmit / receive direction.  It adds a little bit of latency, but testing the firmware I was able to get it down to only a byte’s worth or so.

Here’s a quick render:

And a shot of the actual board:

Unfortunately, I managed to omit a necessary pullup on the enable line of the primary buck converter.  To get things moving along, I blue-wired it under the microscope:

And here’s a shot of it installed on the rpi3 b+:

Sources:

• https://github.com/mjbots/mjmech/tree/master/hw/pi3_hat – PCB design
• https://github.com/mjbots/mjmech_pi3_hat – firmware