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Oh this is fun :) I knew LEDs and microphones could be used as light sensors (and vice-versa), but I would never know the specifics of how to do it. I appreciat

Oh this is fun :) I knew LEDs and microphones could be used as light sensors (and vice-versa), but I would never know the specifics of how to do it. I appreciate this. What other sensors/emitters can be reversed this way?

HarHarVeryFunny 2y ago
You can use a speaker as a microphone, and vice versa.
HeyLaughingBoy 2y ago
DC motors will generate electricity if you turn them by hand, diodes (including LEDs) make very good temperature sensors (not quite what you asked, but it's useful to know, sometimes).
beambot 2y ago
Certain capacitor materials are slightly piezoelectric and can be used as microphones.
r2_pilot 2y ago
It's helpful to step out of the box with those kinds of questions, and consider what it is the sensor is doing. Abstraction is great for programming and reasoning about complex objects like cars (have key, insert key press pedal to move, that kind of thing), but if you're going to use something like a sensor in a way that it isn't designed, you have to go lower in your abstraction level and look at, for example, the physics of what it's doing. Often a thing that emits can receive what it outputs (if you measure how the membrane of an ultrasonic sound generator is moving, for example, although you'd also have to add additional components at which point it becomes a ping sensor), but sometimes it's not feasible. I really enjoyed Practical Electronics for Inventors for this kind of perspective.
regularfry 2y ago
You can measure temperature with a heating element by measuring the thermal noise. Not sure what circumstances that would be useful in, though. I can also remember a project that used the arm of a galvanometer as a very sensitive balance for weighing tiny masses, too, which is the same sort of idea but the way it worked was to put a feedback loop around the voice coil and measure the current needed to keep it locked in place against the weight of the sample. https://www.erowid.org/archive/rhodium/chemistry/equipment/scale.html https://www.erowid.org/archive/rhodium/chemistry/equipment/s... is a copy of the original article which would probably appear at https://www.scientificamerican.com/id/down-among-the-micrograms/ https://www.scientificamerican.com/id/down-among-the-microgr... if I had access.
- kragen 2y ago
  there's a national instruments demo of using this technique to weigh an eyelash at https://www.youtube.com/watch?v=v68Dica16CU https://www.youtube.com/watch?v=v68Dica16CU (although ti claims it's actually them https://www.youtube.com/watch?v=n90whRO-ypE https://www.youtube.com/watch?v=n90whRO-ypE)

HarHarVeryFunny 2y ago

You can use a speaker as a microphone, and vice versa.

HeyLaughingBoy 2y ago

DC motors will generate electricity if you turn them by hand, diodes (including LEDs) make very good temperature sensors (not quite what you asked, but it's useful to know, sometimes).

beambot 2y ago

Certain capacitor materials are slightly piezoelectric and can be used as microphones.

r2_pilot 2y ago

It's helpful to step out of the box with those kinds of questions, and consider what it is the sensor is doing. Abstraction is great for programming and reasoning about complex objects like cars (have key, insert key press pedal to move, that kind of thing), but if you're going to use something like a sensor in a way that it isn't designed, you have to go lower in your abstraction level and look at, for example, the physics of what it's doing. Often a thing that emits can receive what it outputs (if you measure how the membrane of an ultrasonic sound generator is moving, for example, although you'd also have to add additional components at which point it becomes a ping sensor), but sometimes it's not feasible. I really enjoyed Practical Electronics for Inventors for this kind of perspective.

regularfry 2y ago

You can measure temperature with a heating element by measuring the thermal noise. Not sure what circumstances that would be useful in, though. I can also remember a project that used the arm of a galvanometer as a very sensitive balance for weighing tiny masses, too, which is the same sort of idea but the way it worked was to put a feedback loop around the voice coil and measure the current needed to keep it locked in place against the weight of the sample. https://www.erowid.org/archive/rhodium/chemistry/equipment/scale.html https://www.erowid.org/archive/rhodium/chemistry/equipment/s... is a copy of the original article which would probably appear at https://www.scientificamerican.com/id/down-among-the-micrograms/ https://www.scientificamerican.com/id/down-among-the-microgr... if I had access.

kragen 2y ago
there's a national instruments demo of using this technique to weigh an eyelash at https://www.youtube.com/watch?v=v68Dica16CU https://www.youtube.com/watch?v=v68Dica16CU (although ti claims it's actually them https://www.youtube.com/watch?v=n90whRO-ypE https://www.youtube.com/watch?v=n90whRO-ypE)