ALeggeUp's Current Sink Or Swim Build Log

I had a bit of a hard time following the CSOS content, I made it through about half of the videos hoping that I would start to gather what the end goal was supposed to be but I never quite got it. I asked @ChrisGammell for some help and he helped me understand what I might use a current sink for and also pointed me to an EEVblog video that gave more insight

Now that I’ve got a better idea what the CSOS project is all about, I’m going to start into the juicy stuff without feeling so lost.

Created a repo for my CSOS project and I’m currently at the “Creating the initial CSOS schematic” step of the project.

and here is my initial schematic

Couldn’t sleep, needed to fix the pins on TC1016.

In the “Finding a higher rated linear regulator” step of CSOS we find the LM2931, I am going with the same one but I learned something about KiCad schematic symbols that I wanted to share.

The LM2931 has multiple GND pins and as @ChrisGammell points out you should create all of the pins, but when you do you can make all but one of them invisible and put them all in the same position in the schematic and as long as they all have the same name and electrical type they will all be connected. Makes for a much simpler symbol.

I was not a fan of the hierarchical layout, I can see potential uses for it but I was already having trouble figuring out how everything worked together and moving things into different sheets and having to go in and out of sheets was not going to be good. I found it easier to unravel things and break them into blocks all in one sheet so that I could see everything at once and how everything is connected.

I would appreciate it if anyone who has done or understands the CSOS project could take a look and see if it looks like I missed anything.

Thanks in advance for any feedback or advice!

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I found that the BUK9575 that was found in the videos for the MOSFET is now obsolete and unavailable at DigiKey. I found an alternative that I think will fit the bill:

PHP23NQ11T (

I got to the “CSOS Layout Session 1” step and the advice to double check the FET was great, saved me a facepalm moment (well, I got to facepalm before getting the boards).

It looks like they’ve changed the names of the generic FETs and once I took a second look it makes sense. The three letters at the end tell you which order the pins are, so once I knew I was looking for 1-G, 2-D, 3-S I just switched to the GDS part and confirmed it was what I wanted.

Now I know for next time, but I’ll still check because I can see how easy it would be to mess that one up.

Nothing like a rainy long weekend to help get some traction on a project. I was able to finish the layout of my attempt at the CSOS project. Ready to ship off to OSH Park.

and in 3D of course for the final look:


I got a warning uploading my board to OSH Park about unsupported drilled slots due to the oval hole, without going ahead and watching the rest of the videos to see how it turns out I decided to just go with round holes instead and the warning went away.

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These are great updates!

Thanks! I appreciate the encouragement

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Yeah, we have that warning because we can not guarantee plated slots in all circumstances.

We advise replacing small or plated slots with a large via like you did. Typically, setting the hole size equal to the slot length is sufficient to fully replace the feature with minimal design impact.

However, we do have some tips to achieve plated slots for different CAD tools. We’ve developed a solution that works for KiCad in many cases. Please email your .kicad_pcb file to and we can provide specific advice.

Thanks, Drew (


Thanks Drew, I haven’t received those boards yet (they’ve been shipped though), so I’ll see how everything fits when I receive them, possibly by the end of the week. I think it will work fine as is, but it’s good to know there are options if I need, I’m sure it will come up again.

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