Assembly

Now that the software is complete, let’s put the system together!

During testing, I used a 3D printed jig to hold the PCB so that I could easily hook things up to it, and not have to worry about it dragging across the surface of my desk. It’s also useful for making the PCB level so I can easily probe the test points. This setup was great for writing the register level drivers, but I couldn’t test the variable load with it easily.

I used the new setup shown above when I wanted to test the variable load and fan. I also added the heatsink so I could keep the load cool while testing it. The fixture I used above shows how the fan is mounted to the heatsink, and everything is on a platform for the sake of compactness. This is the setup I used to write the rest of the code.

Once I was happy with the code, I designed and then printed the full enclosure. I had a lot of trouble printing something so big, as I got a lot of warping. I got around this by (1) adding brims, (2) reducing the bed temperature, and (3) putting a lot more effort into bed leveling. The print took 32 hours, and 276 g of plastic.

The picture above shows the assembly. First, note the threaded inserts; this will be used to mount the cover onto the enclosure. Second, note the thick green wires; these are 10 AWG and should be able to handle about 30 amps. These wires had to be bent before being assembled since they were so stiff, so they were more like metal rods. Third, the orange wire shows the thermistor going from the PCB to the variable load. The thermistor was taped to the heatsink with a tiny dab of thermal compound. Lastly are a bunch of connectors to the PCB, like the banana jacks for the power supply being tested, and the barrel jack for powering the PCB and fan.

Now let’s look at the variable load, heatsink and fan. I drilled and then threaded holes on the heatsink for the variable load, then mounted it with thermal compound. The heatsink was then put inside the enclosure. Note that the walls and screws keep the heatsink from moving inside the enclosure during transport. The fan was then mounted to the heatsink and the right wall of the enclosure.

Above shows the enclosure with a cover! The LCD is mounted to the cover via screws, and the encoder has threads that are used to mount it to the cover. I also added a power switch to turn the system on and off since connecting and disconnecting the barrel jack was inconvenient.