Measure the mass of an eyelash with a DIY microbalance

[@DavidRichfield]

If you ever do microgram balance work again, I'd recommend using fine copper wire as a quick & dirty mass piece: if you know the diameter you can get the weight per unit length, so there's only one dimension to cut, and it's less susceptible to humidity than paper is.

[@mahmutaksit7715]

it oxidizes

[@w2aew]

Very cool, as always Ben. One thing to be very care with when using gutted meter movements like this is that it is extremely easy for the field magnet to attract any tiny metallic particles into the movement which can easily impede the motion of the coil.

[@michaelmolter6180]

I ruined my first meter this way when I went to drill mounting holes in the metal body!

[@vlogerhood]

What I find most remarkable in this video is your ability to do op amp circuit math. I have a computer engineering degree and basically got through fundamental electronic circuits by doing well enough on everything else that I was able to completely bomb any question involving an op amp. (I still had to take the course three times) I simply could never get the math to work through my brain, and never got the right answer.

[@AppliedScience]

Thanks, I really appreciate it, but I actually missed an important part on this one. As Chris Tacklind pointed out, I don't have a D term, so the loop will be unstable. It's possible that the binary nature of the optical sensor would still make this very difficult to stabilize, but adding a differentiator would certainly help, and is mathematically necessary.

[@ExtantFrodo2]

+Applied Science Why not cut a diagonal into the mask so that it isn't binary?

[@sivalley]

+ExtantFrodo2 The shape of the mask doesn't mater. Once the light transmission level drops below a certain threshold the photodiode will stop conducting altogether. It's the photodiode that makes the sensor operate in a binary fashion, not the shape of the mask.

[@ExtantFrodo2]

sivalley The shape of the mask will change the rate at which the light level changes. With a 90 degree cut the rate of change would as fast as possible. If you had (for example) a vertical cut the rate of change would be zero. Somewhere in between is a reasonable rate of change which crosses the "binary" threshold of the sensor smoothly. With an oscilloscope on the output you might even be able to calculate the necessary angle. In the real world most diodes don't change instantaneously. If you examine their out put at a sufficient rate of speed you can measure the minimum and maximum speed of switching. (It's not even necessarily the same switching on as switching off.) Similarly, there is a narrow, but definite window in the light level threshold the initiates the switching action. To the casual user the window seems like a very square precipice. It's not.

[@sivalley]

ExtantFrodo2 Yes, I understand the shape of the shutter affects the slew rate, but I was merely relaying that the shape of the shutter will not change the 'binary' output nature of the photodiode. The fact that the incident light on the diode affects its effective conductivity more so than the time rate change created by the shutter by orders of magnitude, the slew rate becomes negligible. There are two ways to overcome this magnitude barrier; 1) Instead of measuring the voltage through the photodiode (as Ben is doing with the first op-amp), measure the current which varies much more predictably below the conduction threshold (although not entirely linearly). 2) Use a shielded photo-resistor whose output IS linear with respect to slew rate of the shutter. 3) Operate the system in a differential mode, rather than the direct proportional he is now. Just to recap, I am not saying the shape of the shutter is unimportant, just that in the configuration shown it does not have any meaningful significance.

[@ChrisTacklind]

Nice! This is a 2nd order loop so it needs a PD controller (I is optional). You have only provided a P term. The needle could be counter balanced to minimize the DC current required.

[@AppliedScience]

That's a very good point. It might be possible to stabilize the system as-is with the proper amount of D.

[@NerdNordic]

Applied Science Well, that came out wrong...

[@nThanksForAllTheFish]

Would it still be a 2nd order loop if the coiled spring wasn't removed?

[@sebastiaanhoek726]

I did not understand a word of that, except that he needs more D

[@electronicinvestigations1253]

I've been wanting to get a digital scope for a long long time, but all your recent videos are really making what little cash I have burn a hole in my pocket!

[@philclancaster]

A simple idea that may add some linearity. Have you considered making the IR beam interruptor triangular.

[@stargazer7644]

Put a diffuser over the led slit to make the detector more proportional.

[@OnionKnight541]

All these videos are amazing. It's so rare to see such intelligence and mastery.

[@Stray03]

First time I ever heard of making one with these was actually from a forum back in the early 2000's. It was much more basic where you turned a pot until it zeroed and then did a calculation to figure out how much weight was there. it ended up on hackaday too at one point.

[@electrodacus]

I think in order to be precise you need to apply the measured mass to a single small point on that needle else the position on the measured sample will influence measured weight.

[@RimstarOrg]

A microgram balance. Nice!

[@lunardust201]

I used to work for CAHN instruments, we built microbalances, I used to even wind the coils

[@reedpetersen]

Were their microbalances based on the same operating principle?

[@CharlesVanNoland]

I had an idea for the oscillation issues caused by the tight gradient of the opto-interrupter: instead of using a flat horizontal edge that blocks the emitter use a diagonal one, so that the vertical motion causes a more gradual blockage.

[@0x4C4A]

Such a simple and yet incredibly elegant measurement method. Great video!

[@UberAlphaSirus]

This is in the realms of everything makes a difference. It really makes you appreciate wonder at how awesome meteorology truly is. Especial 100 odd years ago with there equipment and there finding still stand true.

[@didaloca]

Always something absolutely fantastic. Amazing work!

[@antadefector]

Must say, had a similar idea to do a servo measuring of acceleration. Schematic idea was a sourced from ELM home build laser. The servo part, but to be rearranged as linear actuator, not rotational, then the error part would be acceleration while position input would be constant. Very nice idea, nicely done!

[@BenEtherington]

That's a shockingly clever use of an opto interrupter. I'd love to see the system oscillate when unbalanced.

[@dizekat]

Regarding getting more gradual response from the photosensor, you can try turning the sensor 90 degrees and cutting the light blocker at an acute angle, so that the motions to open/close the light have to be larger.

[@martenthornberg275]

This design is actually originally from the amateur scientist column by Shawn Carlson in Scientific American. He credits the idea to his friends George Schmermund and Greg Schmidt. web.archive.org/web/20020606134612/www.sciam.com/2000/1000issue/1000amsci.html

[@ka9dgx]

I think a lot of the temperature sensitivity is from the coil of the meter warming up, if were to make a current source drive the meter, or sample the current out of the meter with a resistor, you would eliminate this source of drift.

[@RayDrouillard]

Oscillation is the bane of feedback control systems. Remembering way back to when I took the feedback control systems class... the system goes unstable when a pole goes to the right of the j-omega axis. In real life, that often translates to having too much gain on the feedback circuit. So, reducing the gain via that feedback resistor pot will probably do the trick. Also, adding a capacitor at a strategic point will slow the system down. For mechanical dampening, put a strong magnet by that aluminum foil that't near the light sensor. The eddy currents generated by movement will buck the magnetic field and dampen the movement. The noise I see on your scope looks a lot like the noise that I used to pick up from fluorescent lights. If you want to fiddle with your circuit more, look up the circuitry that's used for the front end of an EKG. It uses three op-amps (if I remember correctly.) It's designed to have extremely good common mode rejection, and is more noise tolerant than a simpler differential amp.

[@mgabrielle2343]

you could damp the meter movement by wiring a series resistor to the meter coil and an electrolytic capacitor across, so it would slow down a sudden inrush of current and or sudden outflow of (discharge) current, and calibrate accordingly with this damping circuit. but indeed its the way to accurately weigh in micrograms. Resistor can also prevent coil from burning out due to massive overload. Also don't forget photo-interrupters can and do get influenced by external lighting, hence most of the noise can be due to mains light switching at 100hz on a 50Hz mains frequency, as each cycle crosses the zero line twice per cycle, starts with zero and peaks positively, then descends to zero again and goes to negative peak and back to zero.Black out the plastic cover and leave a small viewing window, follow good earthing principles as in audio amplifiers to get rid of hum induced noise.

[@IlluminatedWhiteGuy]

Making your own optical isolator with a cadmium sulfide cell and an LED so the resistance changes in a linear fashion as the beam is progressively interrupted instead of just an on/off arrangement may be helpful.

[@SeanBZA]

Try making that vane a slant, so that it interrupts the beam gradually over a small range. Add extra damping by using a resistor in parallel with the meter movement, lowering the series resistor to compensate. Smallest masspiece I have is a 5mg masspiece, been verified that it is 5mg to 3 decimal places as well, during the last session at the cal lab. The 1g standard was measured at 1.00006g with an uncertainty of 2mg.

[@AtlasReburdened]

You can extend that lever arm to arbitrary length by adding a minute mirror to it and shining a laser off of it. Using sensors to pick up the laser on a wall can easily put your lever arm at 10' and you can easily add an analog range and still shrink the point its servoing to.

[@AmericanLocomotive1]

I wonder if printing out a gradient on a piece of transparency film would give the interrupter a more "analog" response?

[@ceriand]

Or cut the foil diagonally so it's a triangle instead of a square

[@sonicase]

this is what i was going to suggest

[@AtlasReburdened]

Or put a minute section of thin mirror on the arm, shine a laser off of it and put several sensors on the wall to establish an analog range with the sensitivity of a literally perfectly rigid, weightless, 10 foot long lever arm.

[@ZoeyR86]

id put an rc low pass filter on the photo diode line and filter the gain with feedback from the input the to will cancel out (microphone feedback cancellation/ clip limiter ) and give a better reading. another idea is servo the led output or bounce it off the bottom.

[@pangpengmaster]

@@ceriand the slit is so thin, the response is practically still ON - OFF.

[@ikocheratcr]

You could low pass the output that goes to the oscilloscope, with a big cap, small resistor (to minimize resistor noise). There seems to be some oscillation in the signal in the scope, probably servo loop caused; so the RC low pass filter with a cut frequency 10x smaller than that freq you see in the scope can help a lot to get a better "weight value".

[@defaultuser000]

As others have said, try using a light blocking element with an angled edge or a transparency with a gradient printed on it. If the photo-diode still has too much of an on/off sensing characteristic, maybe try a different type of photo-diode, or maybe redesign the circuit to use a light-dependant resistor (LDR). This is a very cool project though. Great ingenuity.

[@AirCommandRockets]

Could you insert an IR diffuser between the emitter and IR detector so that you get a vertical spread of the IR beam? This would turn the point source into an area source. Even if you have to cut the sensor interruptor in half and put them further apart. This way you should be able to get a more gradual amount of IR light entering the detector as the balance comes down.

[@BenEtherington]

Have you seen the parabolic reflector setups they use to image air currents? That's the over-engineered conclusion that my mind jumps to. You might be able to get away with a graduated interrupter, I'm thinking a gradient printed on an overhead transparency might do the trick, if you've got a really high DPI printer.

[@dougfraser2131]

I think you could gain stiffness in your balance by forming a circle from very light plastic and centering it on your meter movement. Attach a platform to the face near the rim. If it was clear plastic, you might print a graduated shade on the disk near the opposite edge and use the disk itself as the beam interrupter. The addition of the graduated beam splitter and the slight mass of the disk may make it easier to damp out.

[@camforman]

I have seen this idea many times before, but few had a nice circuit and involved heavy use of a micro processor. They also lacked the nice video you have. Nicely done. The AC gain (more stability) can be decreased by putting a capacitor between the negative feedback and the output of the first opamp (in parallel with your resistor). The time constant of the filter is roughly the feedback resistor x the cap I am suggesting you add. To add damping for stability you can add a second cap, only this one is in series with a resistor that is approximately the same as the original one used to adjust the gain (exact value is not critical). Adding both the damper and the integrator caps at the start may save allot of grief, as there may be certain combo's that are unstable in very annoying ways.

[@abpccpba]

For even better resolution from the tiny scale place a reflective surface at the axes of the meter. Shine a lazor beam onto the mirror surface which will end the beam on the ceiling surface or for better resolution onto a half circle ribbon. This concept comes from my Cousin Willard Buck back in the '60s. He wanted to measure very tiny changes in gas pressure. He had a man build him a pure quartz curved tube. He attached a mirror at the a axes of two strings attached to the tube and its base. Shining a tiny beam of white light to the mirror he got accuracy from his experiments. Please give my dear cousin many patients a look Willard E Buck. Early on he worked a Los Alamos. Thanks so much for your great channel.

[@Ryzler13]

I think a lot of the noise you are getting is from instability of the platform. eg the fan motor running in your oscilloscope of whatever that thing is and even traffic outside etc.

[@Mythricia1988]

Maybe I'm missing something here but couldn't you just run a long average on the Oscilloscope? The noise seems relatively uniform, and even if it isn't, the bias should be consistent. I don't know, maybe you wanted to just solve the problem entirely on the electronics level, which I'd understand - but from a practical point of view it just seemed like an obvious choice to turn on averaging on the scope... And just wait a little for every measurement, or reset the running average (which I can do with a push of a button on my old HP scope, so I'd expect your shiny new one to be able to do that easily as well). Interesting video either way!

[@nilssab]

I guess there is a high chance he would like to use it without the oscilloscope later on, but yeah, it would be worth testing :)

[@danielssandu5578]

Tens of micrograms!!!! Very interesting indeed! My first idea is to imagine microgravity experiments with your device. Most probably each experiment should be specifically design, to annihilate any electromagnetic noise and to reach the maximum sensitivity for the microgravity event.

[@DasIllu]

Maybe you could modulate the servo with a let's say 1 kHz sine wave and then measure the dampening different masses would cause. Also with an 1 kHz notch filter you then could get rid of most of the interferences caused via EM, sound and static charge.

[@BigParadox]

I once made a totally mechanical balance with a long thin wood rod. I could easily determine the mass of a hair with it. The balance was very simple, it rested on two very tiny ball bearing balls.

[@donepearce]

A bit of averaging and star point ground should do it. Also choose an op-amp with a really low 1/f noise corner frequency.

[@evil-wombat]

Consider cutting the foil into a thin triangle shape, so that it blocks an increasingly large fraction of the beam as it moves

[@aliksashka]

I have an idea. I'm pretty sure it has been done before, but I wonder if it is possible to make a scale that works on resonance frequencies. For example, placing an object on vibrating platform will change resonant frequency of that platform. Then, by adjusting frequency to make it resonant again, it may be possible to calculate the mass of an object by comparing these two frequencies. Thank you very much, I enjoy your channel!

[@vk2zay]

Why would you be building a microgram balance? :) A capacitor across the feedback cap will kill the HF gain and help with stability, as will a series RC shunt to add a differential term in the output drive to the meter movement. Cutting the interruptor flag at an angle might help give it a less steep position sensing gain too. Electrostatic forces will become a major problem at microgram resolution, you should probably build it completely out of (moderately) conductive materials and bond them together. I built a microgram balance years ago using a polystyrene cantilever with a chip of ferrite glued to it. The position was sensed with a permeability tuned oscillator beat against a reference crystal oscillator and the difference term triggered a monostable which was integrated to get a DC voltage. It wasn't very linear at large deflections, but it was exquisitely sensitive. Unfortunately it was a better electroscope, thermometer and seismograph than a balance, but it worked well enough to resolve grains of salt. I think this nulling servo approach is likely to have far better dynamic range than my hack.

[@MilanKarakas]

Neat project. To prevent oscillation, put snubber circuit parallel to the (-)input/output (where is 100 kohm trimmer pot for sensitivity) of the first 'servo' opamp. It consist capacitor and resistor in series, then both paralel with this pot. It should gently dump all rapid changes in voltage or current. If single RC is not enough, then put one more than one RC pairs, but with various different values. For example, 1nF/1 kOhm, 10nF/10 kOhms, 100nF/100 kOhms... Edit: This RC snubber should prevent high excursion of the 'servoing' back, while maintaining relative good feedback speed. For air cover, make glass protective hood. Glass can be electrostatically charged too, but to much less extent than plastics of any kind. For temperature compensation, you may use NTC resistor and some measurement electronic, just to tell you overal temperature inside measuring device, and how much needle may change length (thus leverage length, which may affect precise and consistent reading of the weight). Later, all parameters can be feed into some u-controller including compensating value depending of different device temperature. Callibration of the temperature difference can be done measuring the same weight at different temperatures, then plot error correction values, and so on... EDIT2: Watch out for temperature changes of the trimmer pots - they are very prone to change in resistance with the temperature (I experienced big problems at one attempt to stabilize temperature of the laser for holography porpose - trimmer pot[s] gives me bad behaviour fo the whole circuit, indicating false temerature rising or drop of the laser head, especially when room temperature changes). This small change in resistance is more evident with increased feedback amplification of the opamp(s). EDIT3: I wonder, whether this optocoupler has oppening in form of dot, or line? If line, then it is perhaps possible to roate whole setup 90 degrees, so that shutter doesn't cut beam of light rapidly, but rather gradually. EDIT4: Oh, well. Such opto switch may have slot, but inside is both: photodiode and LED encapsulated with focusing lens, which may produce very narrow beam of light. Maybe making your custom opto switch? I hope this helps.

[@sagaertj]

You could damp by an alu or copper disc between a magnet., or provide a low impedance to the meter. (just short to meter and move it , it will behave different then when left open)

[@RandDiY]

"I hope you found that interesting." I always do.

[@davidliddelow5704]

You could adjust the gain by moving the photo interrupt further along the needle.

[@GlobalOffense]

You're amazingly cool. Thank you for sharing.

[@johnclawed]

This is great because most people can do it! (Of course I also like to see the projects that I couldn't possibly repeat.)

[@T3sl4]

Instead of a pot for variable gain, use an R+C feedback network, with a time constant on the order of the movement time constant. So, probably in the seconds. Pick impedance to match the source -- which isn't very well defined (a photodiode operated photovoltaically has an impedance dependent on intensity...nasty nonlinearity!), so a shunt resistor to set that might come in handy. Offhand, I would guess, 100k across the diode, and 10k-1M in series with 0.1-10uF for feedback. Better alternative: operate the diode in reverse bias and use a transimpedance amplifier (check out photodiode circuits for ideas) to get a stable (and precise) signal, then do the error loop and stuff. For better averaging, just zoom the scope out more. It'll take the average of whatever data you're viewing. More data = better average (and slower updates..).

[@Skracken]

You could try adding an integrating part to your regulator circuit. It should help with oscillations and accuracy I believe.

[@chak7948]

I really like your design. Seems to work quite well and was much more linear than I would have imagined! I took the time to try and estimate how many grains of sugar where in a pound. If every grain weighed the same (of course there all slightly different) but at the weight that you came up with considering my math is correct one pound of sugar would have 6,047,893.333 granules of sugar. Pretty useless information unless if you could guess how many grains in jar of sugar and if you could guess the number you won a truck or something :-)

[@nilssab]

Even more useless information incoming: If you then assume that all granules are of the same size and all are spherical and packed in a FCC lattice, you can calculate the density of 100% dense sugar, and then also the radius of a granule.

[@tmmtmm]

I think what you want is to have the first opamp setup as an integrator with its corner frequency set just below the pole of the system.

[@tmmtmm]

The circuit will inevitably oscillate due to the binary nature of the sensor. The trick it to get it to do it in a controlled fashion and separately lowpass the sensor signal to get the DC output signal desired.

[@Gabbos]

Was that extra foil on the needle a counter weight? Also, put it in a vacuum! :-D

[@antoineroquentin2297]

You, sir, are a genius.

[@AmirHakimiRezaei]

Thanks for sharing, Ben!

[@NickMoore]

I like it. How much torque can you get out of that needle? Enough to put an optical encoder on the other side? If you printed a smooth gradient on clear plastic and used an analog optical sensor you could eliminate the digital jitter.

[@mvtver]

You made static device, balances should be astatic. For this, sensor (optycal sensor and amplifier) should be a zero-detector which works on integrator. Integretor drives current. + input of photo amp should be connected to GND. What is a purpose of first potentiometer? Photodiode should work on short-circuit to be stable, but you apply some voltage. Device used should be on strings, not needles. Also I see periodic nature of noise - to stop mechanical oscillations you need differentiator working parallel to integrator (parallel AC correction).

[@00Skyfox]

If you want the best accuracy put the whole rig in your vacuum chamber. You'll also have to make sure all external vibrations are dampened (such as from the vacuum pumps). Just got done watching all of your videos! Gotta love jobs with a lot of chair time.

[@atmark666]

i think, if you cut the shutter of the interrupter in triangle, you might be able to reduce the oscillation.

[@mikaelkjericsson]

How about cutting the part blocking the optical sensor into a triangle. That might make the reading a bit more gradual. Or perhaps it will just make the system oscillate over a larger span.

[@SlickFungi420]

That was an awesome project!

[@donaldasayers]

I first saw a design like this in the Amateur scientist column in the Scientific American, must be 30 or more years ago. I have had problems with those optical switches being sensitive to ambient light levels being prone to picking up the flicker from fluorescent lighting, despite the presumed presence of an IR filter on the photo transistor. A proportional plus integral control system may give more stability.

[@dtiydr]

Fluorescent lights put out IR as well, just touch the tube and you know so its not strange at all they would react to that.

[@jimhaflinger8185]

The flag should be cut at an angle (45 deg.) to give you some linear range in the servo. I did this in 1975 for a motor servo positioning system. It damped it out quite nicely. Just don't use plastic. A lot of plastics are clear to IR light.

[@cechk01]

I might suggest automatic gain control using a jfet so you dont have to constantly tune the opamp

[@Orbis92]

I am probably a bit too late ;) but if you cut the beam break into a triangle (at its diagonale) and widen the opening of the photodiode a bit (or just use a 3/5mm photodiode) you can build a very cheap contact-less potentiometer :)

[@enriquegonzalez2802]

Interesting approach

[@galileogalilei7844]

Wouldn't a simple photoresistor work better than the photo interruptor? You can get a large range of resistance out of a 25 cent photoresistor. I tried one I took out of a toy and it goes from around 50k ohms with light shinning to 600k ohms in the dark, don't know how linear they are though.

[@eternalblue2119]

Or an appropriate load cell

[@szymon5438]

Photoresistor reacts rather slow so it would introduce a lot of lag, overshoot and unprecisson to the circuit.

[@andrzejpl9897]

Fantastic video and smart circuit . Thanks .

[@kadnify]

Excellent work. Love the ingenuity and reuse. Dumb question: would a slower amp (with a lower slew rate) help? This is nearly a DC circuit; no need for a high BW amp.

[@misium]

Haw about adding a diffuser/lens to the IR sensor, to gather the ir signal from a greater area and make the readings more smooth.

[@Leezorc]

As always brilliant!

[@mdesm2005]

Use an optical interrupter that is progressively more opaque.

[@fir3w4lk3r]

Would a pair of a magnet and a hall sensor work better? Can a piece o Aluminum change the magnetic field?

[@softdorothy]

Hmmm.... oil as dampener? Perhaps a small drop on the "bearing" of the meter might act to dampen the movement.

[@vinzent1992]

That's an absolutely awesome project! now I have to make one myself (:

[@portlandfacts1484]

Look up PID servos. You need a big c feedback then a little differential to speed it up.

[@zarserz]

Interesting. Did you try to use the scope averaging, to maybe get a more stable reading?

[@AppliedScience]

Yes, however the voltmeter in this scope has its own averaging routine, which is not affected by waveform acquisition averaging. The voltmeter was actually doing a pretty good job of ignoring the oscillations.

[@nilssab]

Have you ever made a high T superconductor? with the stuff you have I guess it's possible for you to make a YBCO target and sputter a printed coil on some substrate, and see if you can generate some strong magnetic fields in liquid nitrogen :)

[@nilssab]

also, next step is a small scale MRI ;) not very realistic to try and make one, but anything that would even resemble any feature of a MRI device made at a DIY level would be insanely awesome! :)

[@nilssab]

nilssab I can't guess if it would be harder to make "coils" of YBCO or to cool coils of TiNb with liquid He instead.. Just to make it clear, if you can make superconducting coils and generate a magnetic field with a controlled gradient, you can probably make a simple MRI.

[@sbreheny]

nilssab MRI machines use liquid He because the higher temp superconductors (like YBCO) cannot remain superconducting while generating a very strong magnetic field. In other words, you can't make a very strong magnet with YBCO.

[@nilssab]

Sean Breheny are you sure? I know you need to get fairly below Tc to allow for higher field strengths, but I thought they used TiNb in almost all conventional superconducting devices? And that they are using He because of that.. I know they are trying to make YBCO wires, but I wouldn't think they are employed conventionally anywhere yet?

[@nilssab]

Sean Breheny also what about this? www.magnet.fsu.edu/mediacenter/news/pressreleases/2007august7.html I think MRI devices are generally around 2 tesla at field maxima?

[@JohanStrandberg]

how about extending the aluminium foil for the optical sensor upwards a bit and putting it between two neodymium magnets? You would have to make sure the arm was plastic or something non-magnetic...

[@szymon5438]

Maybe put small magnet under lever and under it hall effect sensor which would output analog value corresponding to distance of magnet.

[@ocayaro]

Sugar is hygroscopic. This could be used to detect humidity. Why stop there, using silica might even improve such detection. Would make a nice high schoool project.

[@slinkytreekreeper]

Impressive stuff as always but wouldn't the moisture off your hand transfer to the paper as you had it in your hand to grab with the tweezers?

[@kl1nk0r]

The "noise" looks more like instability in the control loop.

[@YRohr]

The gain is still too high even if the 100K pot is turned to 0 ohm. The best solution here is to go for an I-controller (or PI) instead of the P-controller you are using. Because speed is not an issue a pure I-controller will do the job just fine. Simply add an integrator between the I/U-Converter and the meter with a long enough time constant. I set up a similar control loop yesterday with a laser and piezo-aktor for an AFM.

[@Shoetiefly]

Enjoyed this experiment. Curious about temp changes on various components. Would a temp change in meter coils register a traceable magnetic influence? How about a linear effect on the needle arm? How about air density effect in the opto? Resistors most effected ?

[@stephanc7192]

Still a great video

[@QuantumFluxable]

Couldn't you put a capacitor in parallel to the photodiode? Voltage across a cap can't jump, potentially giving the OpAmp more time to react and thus oscillate less.

[@AppliedScience]

Adding a cap in parallel to the photodiode would function like a low-pass filter, so that slow changes will be passed, and fast changes will be damped. The problem is that we need those fast changes to get through the amplifier to prevent the meter needle from swinging past its resting point. In fact, adding more low-pass filters makes the oscillation worse because they damp the feedback needed to halt the needle at the correct spot. Adding another opamp differentiator (capacitor in series) will help the situation since it will pass only the high frequencies when appropriate to bring the needle to a halt as it passes its resting point.

[@QuantumFluxable]

Ah, I see. I was assuming the system was unstable because of the fast change from diode lit->unlit and vice versa. Thanks for clearing that up!

[@docelec8199]

Applied Science hey have you tried adding a capacitor across the ammeter this will reduce servo tracking noise very low and tracking loop will become very stable and did you tried intersil precision opamp which have ultra low noise at high gains with compare to ad opamp and gains are selectable by digital pins this will solve your opamp noise problem as i can see this noise which you are seen is opamp noise + servo tracking noise

[@QuantumFluxable]

doc elec That's not a servo though...

[@docelec8199]

QuantumFluxable then what it is plz define and what is a the term "servo " may be my knowledge is wrong about servo term

[@MarysKiril]

Good stuff, very inspiring. I presume the arm is made of aluminum. So I was wondering if adding a small magnet on the side of the movement will not take care of the oscillations by giving you that D-term via induced eddy currents in the movement.

[@MadScientist267]

You don't have a divider in your output from the amp to set the gain. You're only playing against the photodiode, so the gain is inherently high

[@pangpengmaster]

Well spot. Could've been the reason why he said at 1:54 that changing the "gain" doesn't have so much effect.

[@MadScientist267]

@@pangpengmaster Yep basically no matter what that pot is set to, the amp is in open loop until the photodiode comes into play. It also wouldn't hurt to use a ramp/triangular notch or a diffuser in the slot to make the response more linear. The combination should provide much more stability overall. It's a great concept and a creative way of measuring tiny masses using some off the shelf parts... I'd really like to see a revised version at some point. I'd do it myself but I don't really have a need to measure things that small, and he does a really good job of explaining what he's doing and finding. One of the better channels on KZbin, no doubt.

[@DanFrederiksen]

You can try to do an MRI for limbs based on copper coils.

[@MrBranboom]

I like the new channel name! Very pragmatic

[@Mastertim2006]

Hey Ben, I have really come to enjoy your channel content, and I try to watch you as frequently as possible to look what kind of awesome device youre building next. But at your theoretical parts I seem to just lack specialized knowledge :/ Thank you anyway :D

[@AppliedScience]

Yes, I often wonder how technical I should make my videos, and much I should assume the viewers already know. It's a difficult balance, since I want to keep the videos under 10 minutes and demonstrate / explain the video's topic, which leaves little time for background info. I've noticed that Brady Haran often includes separate extended videos (or extra footage) that contain more technical details on a separate channel. This makes editing difficult, since re-using content in both videos would annoy people who want to watch both, and not re-using content would mean leaving out lots of details. I also want to maintain a focus on fairly hardcore technical content since that is the niche that my channel serves -- there are already good topical science/tech channels that cover things with a much larger audience in mind. What do you think?

[@Mastertim2006]

Applied Science I think its definitively a good Idea to keep your style of videos. After all thats why we subscribed to your channel :). And there are indeed a couple of other good technical content producers. Vsauce "BiDiPi" would pop into my mind for example. But I think there is still a big gap regarding the complexity of the presentation between you and Vsauce. But like you said: "That is the nice that my channel seves". And it serves us good indeed :).

[@nilssab]

Applied Science +1 on the thing Hasseltii said, it's still enjoyable watching. That said, I really appreciated the tutorial on impedance you did, so maybe mixing up the content with some tutorials on the technical details would be nice. But mainly I think you should do whatever videos you feel like working on.

[@guggiuggi3687]

Applied Science Some of us are tired of knowing all the answers when watching some of those "broader audience" science channels. Not understanding something can be very freeing, encouraging and motivating. Your channel is perfect the way it is - you should stay within your niche. Recent sub, thanking you for making me feel a little -dumb- bit better about the future of humanity, lol.

[@USWaterRockets]

Is that optical interrupt device they type with an analog or a digital output? The digital type would behave as you describe, where the analog sort would turn on proportional to the amount of blockage of the light. Perhaps it is an analog sensor, but the beam is so narrow that the light is hard to modulate with your mechanical shutter.

[@ipodfixerman]

Wow, impressive work! Just out of curiosity, is the photo interrupter sensitive to ambient light, or is it dominated by light from the IR LED? If it was, would it not be possible for changes in lighting conditions to throw out the calibration, or even for flickering of fluorescent lights to cause oscillation? Thanks.

[@AppliedScience]

Yes, the optointerrupter is not really meant to be used in this way, and is susceptible to ambient lighting changes. Normally, the sensor would be operated in a binary circuit where ambient noise would be small compared to the values of the two desired states. In this case, the servo is riding right on the edge of the transition from off to on, so small ambient changes can cause interference. Shining a flashlight on it, will cause a massive disruption. Even turning on too many fluorescent lights on my bench will cause a very noticeable interference problem.

[@TaggingTechnician]

Thanks! Would trimming the bottom edge of the beam interrupter at an angle improve stability and accuracy? Excellent video!

[@arcadeuk]

Thankyou Ben, this video was very interesting!

[@mohammadr797]

very very coooool! I love that! I got one voltmeter panel around 4K ohm resister! can I use it? if I use it how many micrograms could be measured?

[@NerdNordic]

What if you made the arm longer and put the photo-interupter at the end but kept the "bowl" were it is. Idk, but it feels like that should help with stability.

[@michaelandbrytanyjordan7573]

Very cool. I wish I understood you electronic builds better.

[@artekomx]

Great video. Thanks.