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!
“the fact that the fabulously beautiful planet Bethselamin is now so worried about the cumulative erosion by ten billion visiting tourists a year that any net imbalance between the amount you eat and the amount you excrete whilst on the planet is surgically removed from your bodyweight when you leave: so every time you go to the lavatory there it is vitally important to get a receipt.”
― Douglas Adams, The Hitchhiker’s Guide to the Galaxy
Poo fall in water… Mass of poo displaces the same mass of water (which falls in the pipe), so after the poo, same mass.
Archimedes principle.
What if it’s a waterless toilet like on a train where there’s simply a hole to dump the “ice cream” onto the tracks. In Germany fast inter-city trains often have airplane-style toilets but older trains still empty straight into the Earth, like here: https://live.staticflickr.com/1130/866858409_195c013ce4_b.jpg
A sensor under the toilet seat would roughly weigh you before and after you poop. A sensor under the toilet and above the flange would give you a similar reading, biased with the weight of the toilet plus contents, in addition to noise based on the discrepancies between the density water and the density of the poo de jour
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.
Once again I’m forced to apologize to a user because I accidentally tapped “report comment” on their post, and there is no confirmation OR info on that action. Sorry Hackaday’s comment system sucks, @smellsofbikes. (And sorry, also, that I’m a clumsy idiot.)
OR *undo
It’s not uncommon for heat sinks to be secured with plastic pins that clip into the board and have a spring that pushes the heatsink to the chip. Constant pressure under various thermal expansions and manufacturing tolerances.
This is awesome!
So, it is also a microphone…
The Chinese ones have it by design, the Russian ones have it as redundancy. :D
i wonder what sort of range and accuracy could be had from using a quartz crystal oscillator as a weight scale for very small quantities.
perhaps even as a way to measure very small earthquakes or even local gravity fluctuations if a mass or counter lever were to be added.
Been done, with a decent enough frequency counter and reference you can see the effect of gravity by turning a crystal oscillator 90 degrees
Does anyone know what effect in particular is responsible for offset voltage drift in this case? As i mentioned at project page I expected that using two opposing op-amps would produce a differential signal, but it didn’t., Voltage tracking of both channels is almost perfect. How mechanical deflection is causing change of semiconductor properties?
And secondly this article mensions DIP8 package but SO14’s were used as i had them on hand. Now AI is writing articles on had?
People can make an audio amplifier out of a linear voltage regulator. The schematic was around since 1990