12 ms·
"As part of the calibration, the speed of sound is also a parameter which is optimized to obtain the best model of the system, which allows this whole procedure
by frankus 2y ago
"As part of the calibration, the speed of sound is also a parameter which is optimized to obtain the best model of the system, which allows this whole procedure to act as a ridiculously overengineered thermometer."
Reminds me of the electronics adage: "all sensors are temperature sensors, some measure other things as well."
- Marthinwurer 2y agoI love these kind of inadvertent measurements. One of my favorite examples is that a sufficiently accurate IMU can get you relatively accurate longitude measurements from the Coriolis effect.
- emptiestplace 2y agohttps://en.m.wikipedia.org/wiki/Inertial_measurement_unit https://en.m.wikipedia.org/wiki/Inertial_measurement_unit
- adolph 2y agoSlight correction, latitude, not longitude. The earth’s surface closer to the poles has less distance to travel for any rotation than the surface closer to the equator. As a result the inertial navigation systems of long distance systems must be adjusted. Iirc, this is also the case for artillery firing computations. https://www.oxts.com/blog/going-round-circles-earth-rotation-inertial-navigation/ https://www.oxts.com/blog/going-round-circles-earth-rotation... https://www.britannica.com/science/latitude https://www.britannica.com/science/latitude
- 01HNNWZ0MV43FF 2y agoIs that the same thing where a flat-earther tried to measure something with an expensive laser gyro and kept finding that Earth was rotating?
- adolph 2y agoI think the most you can tell from an IMU or gyro is that there is a change in velocity in a direction aligning with East-West when there is a change in location and that the change in velocity is greater when the location changes in line with North-South. The change in velocity would be greater as one approaches the poles and lesser at the equator. Thought experiment: if I zeroed my IMU at the North pole and traveled in a straight line away from the pole along longitude zero, following the guidance of the IMU. By the time I got to 45° latitude I’d be traveling Westward at 1,180 kph (.95 Mach) to keep the IMU at zero.
- trueshape 2y agoThe flat earther used a fibre optic gyro. You don't "zero" it, it continuously outputs a measurement of its own angular rate around it's sensitive axis. For a 3-axis gyro placed still on earth, it will read about 15 degree/hour around wherever the axis of earth is oriented.
- nielsole 2y agoAsahi Linux (and likely MacOS too) uses the resistance of the speakers coils to detect overheating of same speakers and reduces volume.
- derhuerst 2y agohttps://github.com/AsahiLinux/speakersafetyd https://github.com/AsahiLinux/speakersafetyd
- CamperBob2 2y agoInteresting. If the voltage across the speaker voice coil can be sampled with enough sensitivity at a fast-enough rate, you have an undocumented microphone.
- xyzzy_plugh 2y agoThis is true of all speakers
- CamperBob2 2y agoExactly.
- ssl-3 2y agoIt's true of all dynamic speakers -- the sort with a voice coil and a magnet. (But not all speakers are dynamic speakers.)
- planewave 2y agoWould this also be true for electrostatic speakers as well? Though would probably would require greater gain/amplification or, potentially the application of some kind of bias voltage for the capacitive diaphragm of the speaker. Just speculation based on the shared operating principal with condenser microphones
- psunavy03 2y agoI believe this is one of the initial steps an aircraft INS uses to find north while it is aligning, but it's been too long since I had aircraft systems theory in the front of my brain.
- t0mas88 2y agoYes, from earth rotation the INS could figure out true north if the latitude is known. Or figure out the latitude if current heading is known. But normally it's aligned with a starting position from pilot input or GPS.
- psunavy03 2y agoAs I recall, it's a combination of things all happening at once, to include using last known location at shutdown, GPS inputs (if available) and inertial inputs. There were various workarounds you had to use in the Navy, where the ship has not only usually moved from the last place the jet thought it was, but it's generally moving as the jet tries to re-align itself. GPS made things easier, and there wasn't a whole lot of thinking involved, but it always took the jet a bit more (or a lot more depending on model) thinking to get a stable platform underway.
- VBprogrammer 2y agoIf you are at an airport you will sometimes notice large signs giving Longitude and Latitude of the individual stands at an airport. These are used to give the initial position to the INS via the FMS. Of course these are now all built into the database these days so are only used (if at all) for gross error checking.
- deleted 2y ago[deleted]
- cameldrv 2y agoLatitude or Longitude?
- baybal2 2y ago[dead]
- sam_dam_gai 2y agoDo you mean latitude?
- cushychicken 2y ago> Reminds me of the electronics adage: "all sensors are temperature sensors, some measure other things as well." I wanna say that’s a Bob Pease quote but I can’t find an attribution to it.
- frankus 2y agoI first encountered it in Elecia White's book Making Embedded Systems, but the attribution is anonymous and whom it's attributed to may have heard it elsewhere.
- user_7832 2y agoIs there one saying “All electronic devices are smoke machines, some can compute too”?
- frabert 2y ago"All diodes are light-emitting if you try hard enough"
- bsder 2y agoAh, the light emitting resistor. The moment when you realize why it's called Ohm's Law.
- gavinsyancey 2y ago"All diodes are light-emitting at least once"
- dmoy 2y agoHahaha yea I've seen that in electronics lab a few times. The "temporarily light emitting diode"
- Moru 2y agoI have a Temporarily light-emitting harddrive cable. Really old 40 MB hdd connected to an old computer with a cheap power supply that most likely couldn't handle the slightly lower than standard power in a friends house.
- sitkack 2y agoAll diodes are also light SENSING is you try hard enough.
- immibis 2y agoYou don't have to try hard. Just use it as a photodiode and it magically works. However, if it's inside a plastic case that blocks light, it doesn't. Due to some law about entropy, efficient processes are necessarily reversible. That's why electric motors - some of the most efficient machines ever invented - are also generators.
- Bearsilber 2y agoI just learned how the Duracell Powercheck© worked, which was done with temperature. https://youtu.be/zsA3X40nz9w?si=oGg2wdUlLXSDxpsN https://youtu.be/zsA3X40nz9w?si=oGg2wdUlLXSDxpsN
- entropicdrifter 2y agoIt does act as a thermometer, if and only if the altitude remains constant. The speed of sound fluctuates with both temperature and altitude
- _0ffh 2y agoRight, it gets even worse: Air pressure in not only altitude-dependent but fluctuates even at constant altitude. The pressure (altitude) dependence is comparatively weak, though.
- KeplerBoy 2y agoone might say air pressure changes constantly as we speak.
- adammarples 2y agoIsn't air pressure the only thing that microphones actually measure?
- sojsurf 2y agoAir pressure differentials, to be precise!
- KeplerBoy 2y agoBy definition, sure. But one always needs some effect which changes some electrical property. We can't just hook up an ADC (analog digital converter) to thin air and hope for the best. In practice most microphones measure the displacement of microscopic membranes, which are deformed by the air pressure. The next question then becomes how to measure microscopic movements of a tiny membrane. Turns out the membrane forms part of a capacitor and the electrical characteristics of capacitors depend on their geometry.
- jpc0 2y agoThat is not necessary true. There are at least 4 different types of microphones. Condenser which does in fact form part of a capacitor, dynamic which is effectively a linear generator (coil attached to membrane), ribbon which is a change in resistance as a small ribbon flexes and piezoelectric which is some black magic witg crystals
- kqr 2y agoOh yeah. I realised this the day I discovered my fancy digital SLR was a thermometer: https://entropicthoughts.com/does-my-dslr-have-dead-pixels https://entropicthoughts.com/does-my-dslr-have-dead-pixels
- djmips 2y agoA lot of people like myself consider heat a form of light but I guess a photographer would be just thinking visible light. They say that about 50% of the sun's light emissions comes in the infrared frequencies.
- kqr 2y agoThat seems like a mistake since heat can transfer e.g. via contact without any electromagnetic emission. In fact, that is what I think happens with the sensor also, given that there is an IR filter in front of it. But I may misunderstand your comment.
- pletnes 2y agoVisible light from the sun, or incandescent lights, is also emitted due to heat. Planck’s law is the mathematical relation if you want to know more.
- glitchc 2y agoYup, it's called dark noise. Random generation of electrpns which sometimes find their way into the depletion region.
- danielheath 2y agoBack in high school, I built (with some parental assistance) an apparatus to measure how quickly the pressure would drop (in a pressurized cylinder) when a very small hole allowed air to leak out. Turns out, not only can you measure temperature that way, but can extrapolate the graph out to find absolute zero (IIRC my result was out by about 20 kelvin, which I think is pretty damn good for a high-school-garage project).
- Horffupolde 2y agoNo, there you are measuring R, assuming the air inside the cylinder was an ideal gas.
- analog31 2y ago>>>> Reminds me of the electronics adage: "all sensors are temperature sensors, some measure other things as well." A corollary that's one of my rules to live by: Never measure anything over time without also measuring the ambient temperature.
- mastersummoner 2y agoNot really related, but the way you chose to indicate a comment here immediately made me think you had merge conflicts.
- mnky9800n 2y agoa colleague of mine spent months analysing fluctuations in narrow band signal from a geophone only for a more senior colleague to get fed up with it and demonstrated that actually the fluctuations simply correlate with the air temperature and do so within the spec sheets reported temperature tolerance.
- UltraSane 2y agoThe highest grade gauge blocks use laser interferometry from Mitutoyo have a measured coefficient of thermal expansion AND a uncertainty of that coefficient. And they have a size variance of plus or minus 30nm. That is only about 410 oxygen atoms.