This week I'm starting work on the final project I proposed during week #0. As a reminder, it's a crêpe machine and an integral part of that is the batter pump. What I created this week is a peristaltic pump, which works just like our intestines and although that sounds gross, it has the advantage of being completely food safe because the only component touching food is a silicone tube.
Flexible silicone tube, or, intestines
I designed the CAD for this in Shapr3D and printed the necessary parts on the Prusa i3 MK3S+.
Assembled CAD
Blown-up CAD
Then, I needed a way to drive the stepper motor. I'm using the DRV8428 stepper motor driver chip, and following the application circuit on its datasheet I made the following board:
Design of the PCB in KiCAD
The board is powered via a barrel jack connector and I've included a 3.3V voltage regulator so that the Xiao RP2040 is also powered.
PCB, realized
I didn't get around to making that PCB work, unfortunately. It didn't work first try and it was way too late on Tuesday to debug it. Instead, I went with the Pololu STSPIN820 stepper driver breakout board.
A very important step: be sure to configure the VREF pin on these stepper drivers. It limits the current drawn by the motor and failing to do so can damage the motor and/or the board. In retrospect, that might have been the issue with my PCB.
Tuning the vref potentiometer while probing it with a multimeter
So with that, the motor spins!
Oh yeah and the pump itself doesn't work; the motor isn't able to compress the silicone tubing but I think I may have damaged it somehow because it seems unlikely that it is that weak.