Current Limiter Project Wrap-Up

Four years ago I made my first printed circuit board using EagleCAD and purchased a few units using BatchPCB. It was a version of this current limiting circuit with R5 as a potentiometer, which lets me modify the cutoff current. By the time the boards arrived I probably had exams or something, and so the project was forgotten.

Today I was trying to clean my desk, but I found the boards and got distracted. I scavenged around Sector67 for parts (making backwards progress on the desk-cleaning situation) and populated the board.

When the output draws under some current limit (can be modified by the potentiometer), the green LED is on. When the output would draw more than that limit, the red light turns on, and the output current is limited to what flows through the red LED and resistor in series with it. The concept and operation is described in detail at the Instructables page of the source for this project: http://www.instructables.com/id/PC-Power-12-V-Current-Limiter/

I made the traces thinner than I would have liked. It was my first time getting a PCB made and I didn't realize that I had forgotten to set the trace width until it was too late. The default trace width is probably fine here anyway. It feels good to finally wrap up this project. I could go further with it (compute some values, measure some values, stress test the board, refine the design) but there are hundreds of other projects that will probably take priority.

My First PCB

Welp, I've always wanted to try getting my own pcb fabricated with BatchPCB and it is about time I did so. First things first though--I need a circuit. I found this current limiter on instructables, and I really like it.

While breadboarding this project I ran into some difficulties...This comic I made documents the trouble:


So then it was time to make a permanent version. However I suck at perfboard and my soldering iron is about ten times too hot and has no knobs or anything. So I brushed up on my EAGLE skills.

Hopefully that doesn't look too terrible! Venture Industries is just me paying homage to the Venture Brothers, which is only the best animated TV show ever.

In short, it does this:

• I put it in between my experiments and my power source (usually for me, the 5V line from the USB port of my computer).
• During normal usage, the current my experiments draw is underneath some threshold value. The green LED is lit.
• When my experiment goes awry and the current draw is above that threshold, the green LED turns off and the red LED turns on and the current drops down something small (for example no more than 5V/.47kohm = 25mA).
• My computer doesn't have to shut off the USB ports as a safety measure! +1 to laptop longevity.

Of course, I'm not about to send it off to BatchPCB right now...It's almost 5am. I don't trust myself so much at this hour. So I will error check again after sleep and then send it off. You have something like 12 hours of the posting time to warn me if you see a mistake! GO!

Anecdote: I was seeing a small (.05 or so) drop in voltage from the input to the output. I replaced what looked like a kind of thin, kind of old breadboard wire. The drop disappeared. Science FTW.