Says that type K #thermocouples (#sensors #hardware for use with #electronics), the common kind of thermocouples, work from a couple degrees above absolute zero up to 1260°C, with ±2.2°C or ±0.75% error, whichever is greater. Gives a data table for their output voltages, running from -6.458mV at -270° to 0 at 0° (by convention) to 29.129mV at 700° to 54.886mV at 1372°, which presumably is where they melt, which is about 40μV/°C, with predictable variations from linearity on the order of 3%. #metrology
on 02026-08-19#Witchcraft-and-Alchemy #video about #bootstrapping thinner aluminum #foil material for a ribbon microphone, noting that the usual stuff is about 10μm, testing with a micrometer, while ribbon-microphone #sensors are ideally 1.5–3μm. He reduces the thickness of household foil by etching the foil with NaOH #materials, 4g dissolved in 200mℓ of water (½ molar, he says), which evidently thins the foil fairly evenly. He glued foil to some plastic roundrects to hold it in place during the process. There’s a point where the foil becomes a very fine mesh, some time before being ripped apart by the hydrogen bubbles after about half an hour. He did a 4-liter test to try to hold temperature more constant. I suspect you could get smoother dissolution with the proper regime of #electrolysis, reducing asperities, but he didn’t try that. For thickness measurement, he did the same repeated-folding-in-half thing that I did, but with a micrometer instead of calipers or a ruler to measure the result. He says some of the foil had “the structural integrity of a wet paper towel,” making the process more difficult. The thinnest acts like gold leaf, sticking to his tweezers. The data shows a linear decline in thickness from 10μm at 5 minutes to 0 at 40 minutes, with a 35-minute sample being 2.2μm thick.
So he made some more samples; he tried to etch them for 32 minutes (before a citric-acid stop bath and water rinse) but they fell apart at 25 minutes.
In order to compensate for unknown temperature and agitation variations, he decided to measure the foil’s resistance during the etch process with a constant current. For #metrology, he amplifies the voltage drop across the foil with a differential-to-single-ended converter based on a LM833 dual op-amp #electronics, with an LM317 set up as a 100mA constant-current source, and a couple of relays set up to reverse the current direction through the foil to eliminate any offset errors, including from any unintended galvanic cells. Also he used an angle grinder to cut some blank PCB into a four-wire Kelvin probe so he’s only measuring the resistance of the foil itself, not the resistance of the copper leading down to the foil. The copper is painted black, presumably to protect it from the NaOH. And he’s using something like a Black Pill to record the data.
The 10μm foil is about 70mΩ (=7mV) at first, decreasing roughly linearly with less than 10nm of noise, enabling thinning the foil down to under a micron before it broke.
If you were doing this electrolytically, you could presumably stop the etch directly from the microcontroller with a transistor or even directly from a GPIO.
Then he repeats the etching with a large sample in the same bath with the thin foil strip whose resistance he’s measuring. And then he corrugates his foil ribbon microphone ribbons before etching them to thin them, which answers a burning question I had, and then he recorded the video with the resulting microphone!
An amusing editing trick is that he recorded himself erasing a whiteboard drawing line by line with his finger, then played the video backwards with a voiceover to make it look like he’s drawing with his finger.
on 02026-08-1102025 #paper “A Review: Applications of #MOX #Sensors from Air Quality Monitoring to Biomedical Diagnosis and Agro-Food Quality Control” #CC BY kind of #vapid in a way that suggests AI slop
on 02026-08-11metal oxide semiconductor (#MOX) gas #sensors #electronics #hardware #tutorial
on 02026-08-11#Gelbart #lecture #video #toread on “limitations of servo systems, introduction to #sensors, and #LVDT”
on 02026-07-27“With a 40 megohm resistor the sensor will start to respond 12-24 inches away (dependent on the foil size). Common resistor sizes usually end at 10 megohm so you may have to solder four 10 megohm resistors end to end.” #electronics #touch #Arduino #hardware #sensors
on 02026-05-30#Automotive internal combustion engine crank and cam #sensors use toothed ferromagnetic wheels; they can be “reluctors” that induce currents in a coil with a permanent magnet and variable reluctance or they can be hall-effect sensors that typically produce square-wave output.
on 02026-05-27“FlatCam: Thin, Bare-Sensor Cameras using Coded Aperture and Computation” FlatCam is a thin form-factor lensless camera that consists of a coded mask placed on top of a bare, conventional sensor array. Unlike a traditional, lens-based camera where an image of the scene is directly recorded on the sensor pixels, each pixel in FlatCam records a linear combination of light from multiple scene elements. A computational algorithm is then used to demultiplex the recorded measurements and reconstruct an image of the scene. FlatCam is an instance of a coded aperture imaging system; however, unlike the vast majority of related work, we place the coded mask extremely close to the image sensor that can enable a thin system. We employ a separable mask to ensure that both calibration and image reconstruction are scalable in terms of memory requirements and computational complexity. We demonstrate the potential of the FlatCam design using two prototypes: one at visible wavelengths and one at infrared wavelengths. #DSP #hardware #sensors #cameras #compressed-sensing
on 02015-12-08