The late and lamented [Bob Pease] was one of a select band of engineers, each of whose authority in the field of analogue integrated circuit design was at the peak of the art. So when he remarks on something in his books, it’s worth taking notice. It was just such an observation that caught the eye of [Trashtronic]; that the pressure on a precision op-amp from curing resin could be enough to change the device’s offset voltage. Could this property be used for something? The op-amp as a load cell was born!
The result is something of an op-amp torture device, resembling a small weighing machine with a couple of DIP-8 packages bearing the load. Surprisingly modest weights will change the offset voltage, though it was found that the value will drift over time.
This is clearly an experimental project and not a practical load cell, but it captures the essence of the 2025 Component Abuse Challenge of which it forms a part. Finding completely unexpected properties of components doesn’t always have to lead to useful results, and we’re glad someone had done this one just to find out whether or not it works. You still just about have time for an entry yourself if you fancy giving it a go.
You could attach it to the underside of a toilet seat and indirectly measure amount of poo left behind by user. Signal will be nosy though, you might need a kalman filter.
if you have trouble visualizing the signal, you might try a log scale
( ͡° ͜ʖ ͡°)
That’s easier than weighing yourself before & after!
We build chips that have heatsinks on top, with the heatsink clamped to the board rather than to the chip itself. As in, chip is soldered to the PCB, heatsink is jammed on top of it with thermal compound, and we rely on the manufacturing tolerances being good enough that there’s decent heat transfer between the chip and the heatsink in what is, realistically, an uncontrolled distance.
Well, what if someone messes up building their heatsinks and they’re all 0.2mm of interference?
We needed to figure out if this was going to be a problem, so I got to make something that bolted into the PCB and applied pressure to the top of the package, and then we used water as a weight (we could add more in any amount we wanted so we didn’t need a fancy calibrated weight set, all we needed was a calibrated scale) and we proceeded to moosh the chip in a full automated test setup so we could see if its characteristics changed.
They did but at almost an order of magnitude more pressure than it was possible to exert because the PCB would flex at a lower pressure than where we started seeing things like bandgap changes. Fun project, though, and it was interesting to realize how much packaging affects the die performance.