Strain Gauge Amplifier Board

Made in collaboration with Andrew Greenberg for Portland State Aerospace Society. This was a last-minute overnight project to design, route, and assemble the boards for a next-day test.

The quarter-bridge design uses the strain gauges as one of the four resistors in a Wheatstone bridge, references the bridge to 2.5V, and runs the output of the bridge through an INA125 Instrumentation Op-Amp IC which actually has three op amps in it. We’re using Euroterminals for the strain gauge input and the sense signal outputs.

This is a non-intuitive approach but bear with me. Everything on the board except the purple reversed lettering is on the top side of the board. The reversed purple lettering is on the bottom. I made the boards on the LPKF router that doesn’t actually make two sides of a hole connect electrically … so we’re soldering all the components, including the legs of the connectors, on the top side. The connectors are actually accessible on the bottom side. Just their pins are sticking through to the top layer.

We’ll turn the top side towards the bamboo carrier and use washers to make space so the components aren’t touching the bamboo.

Using a laser cutter to make the bamboo carrier boards.

Our PCB router. Alas, no time lapse.

This is the top side of the board.

And the bottom side.

What it’ll look like.

All ten boards, ten carrier boards, and the parchment stencil.

I was out of town for the stress tests but the team took a ton of photos.