power_dist load test circuit

While testing some variants and new versions of the power_dist board, I wanted to be able to simulate the types of loads that it experiences with a fully loaded robot. Some things are easy, like this capacitor attached to an XT30 connector:

I also have giant power resistors in a similar form factor:

However, a dumb load resistor isn’t a particularly representative load. Most likely, the loads that a power_dist will drive are active loads with switching regulators. When the output voltage is lower, the current will be correspondingly higher. That is especially important when validating pre-charge behavior, because it means that the current is much higher during the initial pre-charge window than it would be for a pure resistive load.

Thus, I made a tiny switching regulator to which I can stick a load resistor to the output.

Unfortunately since MacroFab discontinued their prototype tier, it no longer is as convenient to get one offs populated in the US. So this one I did by hand with a stencil, solder paste, a 3D printed frame, and some new tools, a vacuum pick, and a hot plate. I discovered you can get room temperature stable solder paste now — how convenient!

There were a few bugs… I managed to not have 0603 resistors for the voltage sense divider on hand, but had 0402 of the right values so just stuck a blob of solder to connect them. On the same resistors, I also managed to get the PCB labels swapped. Fixing that resulted in a board that does what it is supposed to!

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