This is my second custom board, and it's supposed to be delivered today! What is it?

Most projects I've seen that have something like a dedicated hot-end circuit board use what's called CANBus. CANBus is a protocol designed for use in cars, where it's electrically noisy, and you have multiple microcontrollers talking to eachother. It's actually a pretty good match for what a 3d printer with multiple control boards is doing. I see why they do it!

But it does have downsides.

For one, you have to use a "CANBus hat" to make your Raspberry Pi talk via CANBus, so there's extra hardware required right at the Pi. And if you're like me and are just using your computer instead of a Pi, you're out of luck. You also cannot use CANBus for everything you use USB for (like updating the firmware on the control boards), so you have to still use USB sometimes in addition to CANBus, and it just seems like a kinda janky solution. And since there isn't any microcontroller that can update its firmware via CANBus, it's not a problem that can be easily worked around.

But what if we could just use USB directly? Low speed USB is not that sensitive. I am going to try connecting everything with just four wires: +24V, Gnd, USB+, USB-. I will derive any other voltages I need on the board on that actual board, and I will use high quality wires to try and shield the USB signals.

Today I will have the board that first tests this idea. If it's a complete abject failure, I will likely know today. If it works today, there's no guarantee that it will be fit for purpose -- adding in the noise of actually using motors might be too much for it.

But let's talk about this board I'm building today. It's basically just a custom USB hub. It takes USB in (from the Pi), ignores the 5V line, sends the USB+ and USB- into a USB hub IC, takes the USB+ and USB- signal(s) from the hub, adds those to a 24V line, and spits it out three custom connectors.

If this were ever a commercial product, this would be the one board everyone would require. It is the heart and soul of the custom parts of these electronics.

The USB hub chip only comes in SMD. Its pin pitch is 0.5mm, which I have done before. The new thing I'm testing on this board is SMD capacitors and resistors (who don't have a pin pitch, and it's hard to find what their "equivalent" is). I am going to try and hand solder those.

But in the future, I want to be working with chips that have pads on the bottom, and pads that aren't visible from the side, and pads with a pitch of less than 0.5. I am going to need something "better" than hand soldering. So I'm also currently working on a reflow oven. I likely won't make a project for that since I am not going to do anything all that custom there. But details of that work likely will leak over into here.

I will likely make one more post here later today, after my package comes in, and I have preliminary results. It might even be pushed into tomorrow. But after that, the speed will slow down quite a bit, because I will have to design, order, and receive custom boards for a lot of these tests. And as I said in the first of these initial posts, I am taking things slow and testing everything.