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Strain gauge made out of PCB

github.com

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Re: Strain gauge made out of PCB

#21

Post by kragen »

userbinator wrote: post #19
kragen wrote: post #17

Earlier quoted context omitted.

At some level it becomes expensive, but it's far from clear that five significant figures of mass is that level. A US$2 quartz watch measures time to 5½ significant figures, US$10 multimeters routinely measure voltage to 4½, and US$5 GPS receivers can provide you with time measurements accurate to 40ns that inherit the drift of world metrology standards, a precision of 16 significant figures if you are measuring a lo…

Where are you finding $10 4.5 digit multimeters?

Hardware store, usually. 3.5 digits is common, 4.5 digits less so.

Re: Strain gauge made out of PCB

#22

Post by bitdivision »

amelius wrote: post #20

Can anyone explain why the BRIDGE_SUPPLY voltage is connected to the voltage regulator output and PWM signal at the same time (through the FSA5157L6 analog switch)?

I don't think it is. PWM_BIAS is used as the select for the analog switch. High connects COM to B1 (GND) and low connects COM to B0 (BRIDGE_SUPPLY).

Re: Strain gauge made out of PCB

#24

Post by amelius »

bitdivision wrote: post #22
amelius wrote: post #20

Can anyone explain why the BRIDGE_SUPPLY voltage is connected to the voltage regulator output and PWM signal at the same time (through the FSA5157L6 analog switch)?

I don't think it is. PWM_BIAS is used as the select for the analog switch. High connects COM to B1 (GND) and low connects COM to B0 (BRIDGE_SUPPLY).

Ah yes, you're right, my bad.

Re: Strain gauge made out of PCB

#25

Post by qwery »

amelius wrote: post #18

> Thinner boards will result in a smaller output voltage swing. For the same weight? I would expect the opposite.

For the same deflection, I assume.

The device effectively measures mechanical strain at the surface of the PCB. The surfaces of a thicker board will experience more strain from bending because the radius of the curve (at the surface) is greater.

Re: Strain gauge made out of PCB

#26

Post by thirdhaf »

kragen wrote: post #17
dogma1138 wrote: post #15

Earlier quoted context omitted.

Precision and accuracy is very expensive there is a reason why high end measurement equipment costs as much as it does.

At some level it becomes expensive, but it's far from clear that five significant figures of mass is that level. A US$2 quartz watch measures time to 5½ significant figures, US$10 multimeters routinely measure voltage to 4½, and US$5 GPS receivers can provide you with time measurements accurate to 40ns that inherit the drift of world metrology standards, a precision of 16 significant figures if you are measuring a lo…

As a quick and dirty rule of thumb measuring parts per million in anything except time or frequency will get expensive. Temperature drifts will cause expansions and contractions on that order if you’re measuring lengths.

Re: Strain gauge made out of PCB

#27

Post by stavros »

kragen wrote: post #14
s0rce wrote: post #6

Earlier quoted context omitted.

My dad built one with an electromagnetic coil many years ago, can't find the design, capacity was limited but had 100? microgram resolution, maybe similar to this applied science video https://www.youtube.com/watch?v=ta7nlkI5K5g but I think simpler. maybe something like this: https://www.erowid.org/archive/rhodium/chemistry/equipment/s... https://www.erowid.org/archive/rhodium/chemistry/equipment/s... I found some ol…

Thanks for the reference! If you do find the link maybe it will be in the WABAC machine.

That's the most interesting misspelling of "wayback" I've seen so far.

Re: Strain gauge made out of PCB

#28

Post by bialpio »

stavros wrote: post #27
kragen wrote: post #14

Earlier quoted context omitted.

Thanks for the reference! If you do find the link maybe it will be in the WABAC machine.

That's the most interesting misspelling of "wayback" I've seen so far.

TIL it may not necessarily be a misspelling: https://en.m.wikipedia.org/wiki/Wayback_Machine_(Peabody%27s...

Re: Strain gauge made out of PCB

#29

Post by stefan_ »

knotimpressed wrote: post #3

For a long time I've been trying to make a DIY milligram-accurate scale, and milligram-accurate strain load cells are expensive. Does anyone know if the resolution of this is high enough?

Shahriar has a video on repairing a milligram resolution scale: https://www.youtube.com/watch?v=Lz9mBc6FGzE

They don't tend to use strain gauges I think.

Re: Strain gauge made out of PCB

#30

Post by kragen »

thirdhaf wrote: post #26
kragen wrote: post #17

Earlier quoted context omitted.

At some level it becomes expensive, but it's far from clear that five significant figures of mass is that level. A US$2 quartz watch measures time to 5½ significant figures, US$10 multimeters routinely measure voltage to 4½, and US$5 GPS receivers can provide you with time measurements accurate to 40ns that inherit the drift of world metrology standards, a precision of 16 significant figures if you are measuring a lo…

As a quick and dirty rule of thumb measuring parts per million in anything except time or frequency will get expensive. Temperature drifts will cause expansions and contractions on that order if you’re measuring lengths.

Yes, but in this case we're measuring weights, not lengths, and we're looking for 5 sig figs, not 6.
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