Wednesday, January 20, 2010

DIY Oscilloscope

I built the Sparkfun / JyeTech DIY oscilloscope today. The Sparkfun version comes with the surface-mount components already installed, leaving me with only the PTH components. Which probably explains why I was able to put it together with a minimum of trouble, and why it works now. Soldering a zillion surface-mount components would've been ... exciting, and probably well beyond my soldering skills at this point. I'm assuming that Sparkfun did the surface-mounting. They did a great job, as far as I can tell.

The assembly instructions are unbelievably full of suck. The first item pretty much set the tone: "Only install parts listed in the part list attached with the kit. Ignore components that appear in schematic but not in the part list." Which is certainly an ... interesting approach. Why print two sets of documentation (and of course by "print" I mean "generate PDFs") when you can print one? Users? Hah! Maybe I was just spoiled by Lego and Heathkit directions.

On the off-chance that someone other than me reads this post in the future, some warnings:
  1. Make sure to look at the picture before installing the voltage regulator. Note that there's a heatsink under said regulator. I did not. I installed the regulator, clipped the leads, and only then realized that I should've put the heatsink under it first. I'd also never used desoldering braid before (and didn't have any), so removing the regulator was all sorts of fun. Lucky for me, a) regulators are pretty tough, and don't seem to mind a little heat, b) swearing, pulling, and heating are sufficient to remove a 3-pin device without using braid, and c) I didn't have real wire-cutters, which meant that I hadn't cut the pins terribly short, which in turn meant that I still had enough length to reach the holes when I put the heatsink in.
  2. Point 5 in the notes mentions shorting JP1. Ok, do that. Don't unshort it -- you need a shorted JP1 to have a working oscilloscope. This becomes clearer once you look at the schematic. If you don't leave JP1 shorted, the LCD backlight won't turn on, and you'll measure unexpectedly-low voltages going into it.
  3. Remember to attach the 3-position switches facing the right direction. *cough*
With that all done, I now have my own working (and very inexpensive) oscilloscope. Yay me. Now I need to get a little further on in AoE so I can really use it.