Scope to read oscillations of a watch.  - Page 1
Forum section: electronics / beginners

author: JTknives
author_rank: Contributor
timestamp: October 22, 2022, 02:38:12 am
content: I do watch repair as a hobby as well and I have ran into an issue. I am wondering if I can use a microphone attached to a scope to read the beat rate of a watch. One of the watches I work on is an accutron which where made in the 60s before quartz. It has a tuning fork that vibrates at 300Hz and an electrical circuit and coils to input pulses back into the fork to keep it running. The issue is that modern watch timegraphers can’t measure the beat rate of these. So I need a way to pick up the 300Hz hum and measure to make sure it’s 300Hz. If it’s off then the watch will run fast or slow. I have practically zero experience with a scope besides a few simple tests I used one for in collage. I guess being that it has an electrical circuit I could probe it to get the single. As the tuning fork has magnets and a pickup coil that triggers a transistor. Any help you can provide would be amazing, thank you JT.

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 02:55:48 am
content: I'd probe it directly TBH.You could use a microphone into a computer and a mediaplayer with a frequency spectrum effect - that'd get it done. That said computer clocks are terrible anyway (they gain or lose ~10s of seconds per day, I'm not sure if they were always this bad (as a kid I don't remember setting them that often and they weren't net connected) or if we just rely on NTP these days)Why can't you just probe it electrically and count the waves on some time division? For example a wave with a period of 1ms would be 1khz. This will still be a little off BTW, but I suppose it'll get you closer.Can you not just tune it empirically, if it gains slow it down a bit if it slows speed it up a bit?

author: Dundarave
author_rank: Regular Contributor
timestamp: October 22, 2022, 03:07:04 am
content: A small piezo electric disk element in direct contact with the watch might work. It might generate a current large enough for a direct reading with a scope probe on the leads of the disc.Another thought: since you know that the frequency is going to be very close to 300 Hz, I’d try making a little loop of wire, connect it to the scope probes, set the time base for 300 Hz, set the input to max, and hold the loop very close to the watch circuit, and see if you can pick up the impulses via magnetic coupling to the little watch coils.

author: JTknives
author_rank: Contributor
timestamp: October 22, 2022, 03:11:08 am
content: Thy can be very accurate watches. It’s what was use in the space race. Thy advertised an accuracy of 99.9987%. So that being said it would take along time to adjust it by just running it. The very slightest adjustments on the weights on the forks can adjust it +-2 sec a day. But if you know the actual Hz you can get it set perfect the first time.

author: JTknives
author_rank: Contributor
timestamp: October 22, 2022, 03:19:08 am
content: The hum is actually loud enough that you can hear it from about a foot away. If you have it on your night stand you can hear it while you sleep.

author: Dundarave
author_rank: Regular Contributor
timestamp: October 22, 2022, 03:35:13 am
content: Quote from: JTknives on October 22, 2022, 03:19:08 amThen I’d try a microphone for sure, what’s to lose?. But I’m also thinking that a scope may not give you the resolution you need to get to exactly 300Hz. Probably an accurate frequency counter is what you need instead.

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 03:44:46 am
content: Quote from: JTknives on October 22, 2022, 03:11:08 amI promise you in this case you are going the wrong direction, you'd need a VERY good time standard to get 300hz accuracy to the error of ~ seconds a day. Computer clocks are terrible for example so "is this 300hz" - not the way to go. NTP can get you to good LONG TERM accuracy though, but not short term (short term your computer would be more accurate, because of network deviation)https://en.wikipedia.org/wiki/Allan_varianceThis might get you started.The error accumulates, say you wanted to measure the thickness of a sheet of paper, it'll be far more accurate to measure 500 sheets with a ruler than it would be to measure 1 sheet with calipersWe can go through the numbers if you have yet to be convinced. I thought it was broken or something not that you were trying to calibrate it.You can get a PPS from pretty much any GPS (you may need to find the circuit board) - but using this would be the wrong direction.

author: Bud
author_rank: Super Contributor
timestamp: October 22, 2022, 03:58:08 am
content: You cant get measuring such precision with oscilloscope. You are talking 10^-3....10^-4 Hz, milli Hertz range. Not sure if even a frequency meter can get you that. A possible solution may be to have a precision digital oscillator source with the required accuracy, feed it into the X input of the oscilloscope and feed the watch signal into the Y input of the oscilloscope, this will produce a Lissajous figure on the scope in XY mode. Then tune the watch until the pattern stops moving. This will indicate both frequencies match exactly.Edit: For this method you'd need first to get the amplitudes of the reference generator and the watch signal comparable (close in amplitude to each other), this will produce a circle on the XY scope, serving better as the adjustment indicator.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 22, 2022, 04:18:39 am
content: Have you tried one of the unofficial timegrapher programs/apps like Watch-O-Scope (http://www.watchoscope.com) or one of the phone apps. I've been impressed with 'Watch Accuracy Meter' on Android. I just use it with the built-in microphone. I use a squishy silicone cover on my phone and I think that helps isolate the microphone from external noise when I press the crown against the microphone hole. Whatever program you use, It might choke when you try to set it to look for 1080000 bph.I like Dundarave's idea of a loop of wire. Inductive pickup will prevent audio interference from distorting the signal. Make the loop large enough so that you can insert the watch into the hole in the center of the loop and then rotate the watch until you get maximum amplitude.If you have a scope, why not try probing the circuit directly? Use a x10 probe and see if you can find a spot to probe that doesn't affect the frequency.Regarding accuracy, an error of 5 sec. per day would be a frequency error of about 0.017 Hz on a 300 Hz signal. That's easy to measure with a frequency counter, but could be a challenge with a scope, depending on how good your scope is.

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 04:20:14 am
content: Quote from: Bud on October 22, 2022, 03:58:08 amYeah seriously see what I said, if you want we can go through the numbers of why but basically without a frequency standard, I, armed with 24 hours and "ntpdate -q", will be able to measure the error far better than you.Computer clocks are crap BTWThis is with NTP sampling every 30 seconds:Okay the clock looks "OK" right? Little slow? (This is reasonably good as they go)Let's subtract that!WhoaTrust me on this, I've had to involve a GPS to get accurate interval measurements (not sure about time still!)

author: tanveerriaz
author_rank: Contributor
timestamp: October 22, 2022, 04:24:02 am
content: https://www.watchuseek.com/threads/open-source-timing-software.2542874/

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 06:03:37 am
content: Quote from: tanveerriaz on October 22, 2022, 04:24:02 amReally glad such a thing exists (wish the author had known about wxWidgets) - this is only as good as the computer's clock, they suck now-a-days.When I was a kid I wasn't allowed online (I was huge jailbait it seems) and I didn't set my PC much, my theory is they've gotten worse as the computer clock itself is crap. There's also like 6 different clocks (TSC and some system clock are most common)But it is a good "order of magnitude" guide - but remember you could do better with NTP and 24 hours.

author: JTknives
author_rank: Contributor
timestamp: October 22, 2022, 07:14:56 am
content: I don’t have a scope, but had considered buying one if it would do what I needed. I can buy an old vibrograf for a few hundred clams off eBay but was kinda hoping there would be a modern solution that was more accurate.

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 07:34:46 am
content: Quote from: JTknives on October 22, 2022, 07:14:56 amThere is (again) - they're called frequency standards and counters.You can buy second hand clocks (proper ones, like atomic standards that are obsolete but still far far better than anything near by), you can calibrate them reasonably well with a GPS and a few weeks.But now your watch is crap compared to them, you can breath near your watch and cause the timings to change, but hey you'll notice!I think you should do some experiments....I would say note your computer's or phone's time every now and then but they'll change (they'll use NTP to check the actual time then drift the clock into sync, or just suddenly jump and set it), measure it against other watches or something.If this has a mechanical system that moves substantially, air pressure and humidity are next.I know you're probably ignoring what I've said because it's not what you want to hear but look up Allan Variance (which i linked before) - EVEN IF you get the best calibration you can in say a few minutes with a frequency standard, that's not the same as long term accuracy!Explicitly: Me with "ntp-date -qv" 24 hours and the watch can lead to a better long term accuracy than you calibrating it to a high standard with a frequency standard over the course of say 15 secondsOh I missed one: magnetic fields!Addendum: That program the other guy linked looks pretty good, but that will be limited by the computer (obviously), if it's using say the TSC don't hope for much (this ticks at ghz), the system clock (separate on the motherboard and why we have batteries on them) are better- these tick a a few mhz I think, either way it's better long termThe TSC is also derived from the master clock (100mhz usually, 133mhz for older stuff, 33, 66 for ancient stuff maybe) which isn't for time keeping anyway.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 22, 2022, 08:40:11 am
content: Quote from: edpalmer42 on October 22, 2022, 04:18:39 amThe downside of inductive pickup is that 300Hz is a harmonic of both 50Hz & 60Hz power frequencies, so noise from that source may be a problem.Of course, youcouldintentionally compare the Mains frequency with the 300Hz using Lissajou figures, as the grid frequency has pretty good long term stability.

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 09:01:15 am
content: Quote from: vk6zgo on October 22, 2022, 08:40:11 amNice.

author: iMo
author_rank: Super Contributor
timestamp: October 22, 2022, 09:03:32 am
content: I've been wearing an automatic watch since ever, so no idea how your watch sounds, but I made myself a probe consisting of a piezo sensor (the coin sized piezo buzzer, mechanically connected to the watch case) with a pre-amplifier, feeding the signal into the mic input of a sound card. In your case I would feed the signal into a counter and looking at the frequency. You would need a longer time base like 100+secs, or a reciprocal counter with a time interpolator (in order to measure the frequency to say 5-6 digits). Other option could be to measure the beat as indicated above, the issue with it could be the sound includes the noise of other mechanical parts inside (the wheels etc).The inductive coupling to the coils seems to me the best option (a pick-up coil w/ a preamplifier, and do use the counter as above).

author: Kleinstein
author_rank: Super Contributor
timestamp: October 22, 2022, 09:29:52 am
content: As one can usually hear the ticking of a mechnical clock, a microphone can pic this up too. Even the cheap microphones are about as sensitive as the human ear. One may want some acoustic shield to keep out external noise.A piezo in direct contact can be more sensitive - sound travels very well through dense materials, like metals. It is at least wroth a try, as those piezo discs (I would prefer a rather small one) are widely available and fun to play with as a sensor.If the signal is good the scope may work. A PC sound card could be a good alternative too and could do better noise filtering, at least in theory. I would expect those software made for this purpose to work reasonably well. I have not checked lately, but I would not expect the sound cards to be that bad. This absolute accurcy for sure sucks and the drift with temperature may also be poor, so one would have to also measure some reference frequency from a known source. Some 23 years I have done frequency measurements with a sound card, and it did work pretty well, essentially limited by the stabilty of the crystal on the sound card. There was no need for a long time base - 1 second was OK for some 8 digits AFAIR. It however depends on the quality of the input signal, but that is the principle limitation. With a noisy and more sine like signal to start with conventional frequency counters may well be more limited than the SW analysis of the sampled signal. In most case the front end is limited and would need a clean signal (maybe external analog filtering with all it's limitations) to get good results.

author: jonpaul
author_rank: Super Contributor
timestamp: October 22, 2022, 09:35:38 am
content: leo Bodnar GPS DSO, generate 300 Hz to GPS accuracymic or coil, pickup 300 Hz watchScope XY lissajou figureJon

author: iMo
author_rank: Super Contributor
timestamp: October 22, 2022, 09:38:26 am
content: Another option is to measure the signal directly on the oscillator inside the watch. Careful coupling (via a small value capacitor or a large resistor) into transistor's base or collector could also be worth of trying. Not sure how, say a couple of pF of the probe load, would de-tune the frequency, however..PS: I doubt you would need GPS based accuracy in order to monitor the accutron watch. Its mechanical tuning fork frequency depends on temperature, position, acceleration, battery voltage etc. So I would not expect better parameters of the watch than a $5 crystal based watch.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 22, 2022, 09:46:41 am
content: I made a beat meter for a school clock using a breakout board for the MAX9814 microphone amplifier from Parallax, PIC12F1840, and ascii character display that I had on hand. As shown in the schematic, I also had a scope output. I used the scope but provided the numeric display so my granddaughter could also use it at her home.Schematic, board pictures, and Assembly code attached.I could detect the beat of my Timex wristwatch but did not try to measure the crystal frequency.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 22, 2022, 09:54:29 am
content: An oscilloscope would be less accurate than a sound card.For 300Hz I'll use apiezo diskas a microphone, and a sound card to record the signal. From the sound card you can post process the recorded sound (e.g. withAudacityor other program), to find the exact frequency.Alternatively, use aprogram to simulate an oscilloscope(using the signal captured with the piezo disk + sound card), and use the Lissajous method described above, live. That oscilloscope program has a signal generator, too.The software is free, and a piezo disk can be found in most of the toys or even wrist-watches that can beep, or it can be ordered for a few cents.

author: magic
author_rank: Super Contributor
timestamp: October 22, 2022, 03:22:40 pm
content: A sound card would be less accurate than an oscilloscope.You have no idea what's the exact sampling frequency of a soundcard, but oscilloscopes at least come with a spec sheet and some sort of declared "horizontal" accuracy. My Hantek has a built in frequency counter with 5 or 6 digits resolution (I forgot) and it is fairly stable after a few minutes of warm up and unlikely to be any less objectively accurate than any random dodgy crystal in a random sound card.I would trust a scope before a soundcard. Either way, you are not getting excellent absolute accuracy without a highly accurate reference clock anyway.editEhm, wait, there is one problem with that. Those dumb frequnecy counters (like in my scope) simply count cycles per second or something like that, which is absolutely hopeless for 300Hz - 2.5 digits resolution

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 03:38:10 pm
content: Quote from: magic on October 22, 2022, 03:22:40 pmThere are a few things in play here....Pretty much any scope will be crap as a time standard. That is if you set it to say 1us/div the relative error of what you get will be quite high You may get 0.99 us/div or 1.01 us/div for example.Keep in mind for clocks on this order the first thing you need is a little heater to keep the temperature constant, they're sealed so forth.Let's suppose your "scope us" is "p" (in "real us" - eg p=1.01) and you want 1 second worth of those, that's now 10^6 p of time, if you want a day that's 8.64e10 pRe writing p as (r+e) where r = 1.0 (us per real us) and e is your error (so p-r=e or p-1.0 =e or e=0.01 for our example) now the "real time" of a scope's day 8.64e10 (1+e) = 8.64e10 + 8.64e10 e (I shouldn't have used e for error, sorry, go with it!)subtract a real day:error is 8.64e10 e us /dayLet's suppose you get 3 digits (that's 10 ns accuracy)this is a fictionally good to maintain this over the operating rangeso |e|=0.001 say or 1e-3, now the us/day error is 8.64e7Converting to seconds:86.4 seconds off per day!Which is crap for timekeeping.As for your frequency/counter thing, this consists of two parts:1) Counting - which is relatively easy2) Timing - the difficult bit. This is because we often don't want a counter just by itself.GPSes know the time very accurately (this is how they work) and have a PPS (pulse per second) output and is long term as stable as you can get.Check out that Allan Variation thing above.BTW most clock generators for digital circuits are far far worse than this.I've dug deep down this rabbit hole.There is probably such a thing as a "time calibrated scope" BTW, I don't doubt it, but they're not your generic 'scope, if those have a calibration sticker assume volts not seconds!This "calculation" assumes that the time period of your clock is stable, this is another big if and it's why calibrating the watch is a lost cause, the mechanism is exposed to air, pressure changes, earth's magnetic field (seriously), humidity, so on.Clocks are crap by and large!Your computers and phones are kept in sync by an NTP client.

author: iMo
author_rank: Super Contributor
timestamp: October 22, 2022, 03:48:37 pm
content: FYI -http://www.leapsecond.com/pages/sound-1pps/You have to sample for at least 200 seconds with simple gating counter to get a resolution which matches the theoretical Accutron precision (I would expect around 2 secs/day best case).Another option is to use a "reciprocal counter", where you utilize a time interpolator - thus you get many additional digits in a single measurement. With 360Hz Accutron frequency and 10MHz OCXO counter reference you get 27777 integer reading every second, plus typically 3 additional digits from the interpolator..

author: BeBuLamar
author_rank: Super Contributor
timestamp: October 22, 2022, 03:53:18 pm
content: Quote from: JTknives on October 22, 2022, 03:11:08 am2 sec per day is kind of a standard accuracy for a quatz watch. High precision ones are better yet can a scope measure the frequency with that kind of accuracy?

author: JTknives
author_rank: Contributor
timestamp: October 22, 2022, 04:26:59 pm
content: A lot of what you guys have said is over my head as I have not used a scope or frequently counter befor. But I get the gist of what your talking about. The real high end time graphers do use a pizo pickup and actually output the sound through a speaker as well so you can hear how healthy a mechanical watch is. Yes I know lots of things affect a watch but thy are generally tuned in a few positions as thy will be worn on a moving wrist. So you shoot for a best of average of around +5sec a day. Bulova who made the accutron does have a new quartz watch now thy claim is accurate to 10sec a year which is what most quartz watches hope to reach per month. It has a 3 pronged quartz oscillator running at 262 kHz which is 8 times faster then a standard quartz. I guess I could use one of those as a time standard.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 22, 2022, 04:39:58 pm
content: You might seriously consider a MAX9814 microphone amplifier board. It seems I probably used the Adafruit rather than Parallax. Those BOBs are cheap and can be connected directly to an oscilloscope. They are even on ebay and Amazon.Once you look at the sound with a scope, you will see a lot of "noise." That is, background, vibrations, reverberations, and bouncing. That's the reason I used a small MCU to clean it up and give a nice square wave. However, the scope sweep may be enough for your purposes. All you need is a battery or power supply, BOB, and oscilloscope.

author: bdunham7
author_rank: Super Contributor
timestamp: October 22, 2022, 05:06:43 pm
content: Quote from: py-bb on October 22, 2022, 03:38:10 pmScopes would be calibrated both horizontally and vertically, but a typical CRO would have permissible errors of 1-3% in both directions, so not so good for this purpose. However, almost any reasonably decent modern DSO will have a sample clock that is accurate to a few ppm, so the only remaining question would be whether it has a frequency counter function that works well enough. A quick test of my two Siglent DSOs reveals that while they would work just fine for an ordinary quartz watch at ~30kHz, they just don't work well enough at 300Hz even with silly-long acquisition times. You need a universal or reciprocal type counter for low frequencies. An HP 5316B (w/ OXCO timebase) measuring a 300Hz signal from an AWG gives me a stability and (indicated) accuracy of <0.5 ppm, more than good enough for a watch.

author: py-bb
author_rank: Regular Contributor
timestamp: October 22, 2022, 05:10:08 pm
content: Quote from: bdunham7 on October 22, 2022, 05:06:43 pmI don't think the "master clock" it divides down/multiplies up is on the order of ~1e-6 error.Crystals of 1e4 are not cheap.If you open it up and it is that accurate there'll be a big metal "tank like" think (you know what a crystal looks like) - what's it say on it? It'd need 6 digits to be on 1 part in a million, but to make use of that it'd also have to be temperature controlled, that's a hell of an ask.(provided this is a "generic" scope, I am sure there are some super timing ones out there ofc)

author: bdunham7
author_rank: Super Contributor
timestamp: October 22, 2022, 05:33:21 pm
content: Quote from: py-bb on October 22, 2022, 05:10:08 pmI imagine they'll use a COTS TCXO or VC-TCXO if they want to be able to calibrate it. These are readily available with stabilities of a few ppm and only cost $2-3 in small quantities, probably less in volume.https://www.mouser.com/datasheet/2/137/TG_5006CG_en-1003199.pdfThe AWG I mentioned earlier uses a simple, cheap VC-TCXO like this and the combined observed variance with my OCXO counter is well under 1ppm. As in the first 7 digits are completely stable (and accurate) and the eighth wanders +/- 5 counts max.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 22, 2022, 05:56:52 pm
content: Good Morning JTknives, Did you ever guess that a rabbit hole could be this deep?.....I'm very surprised myself.

author: magic
author_rank: Super Contributor
timestamp: October 22, 2022, 06:04:49 pm
content: Quote from: JTknives on October 22, 2022, 04:26:59 pmWell, so why are you asking about a scope? I suppose you would need to buy one if you decide to use one.Scopes as such are usually not equipped to measure low frequencies with high resolution, though as I said, even my cheap-ass DSO can measure high frequencies to high resolution and 50ppm declared accuracy (I just checked the specs).A scope could be useful to observe the shape of the waveform coming from whatever sensor and amplifiers you might choose, to confirm that stuff is working the way you think it does, but at such low frequencies a soundcard recording could work for this purpose too.Once it is established that the circuitry produces a clean waveform of sufficient amplitude, you need to measure its frequency. The PRO option is to use a high resolution, reciprocal frequency counter, and I honestly have no idea about such gear and can't recommend anything. The NOOB option is to try to hack something together with a soundcard and software. It could be a bit of PITA to set things up on the software side, or maybe you will be lucky and find something suitable quickly. The accuracy of sampling rate of soundcards is a massive unknown, but it could be calibrated by measuring a known good 32kHz watch crystal oscillator. That's within the bandwidth of modern soundcards, even of the sort you will find integrated on motherboards, in laptops, etc.I'm not convinced that getting a scope is the best option here, unless you wanted a scope anyway and simply look for justification

author: jpanhalt
author_rank: Super Contributor
timestamp: October 22, 2022, 06:39:23 pm
content: A scope plot will need to be cleaned up, as mentioned. Attached are images of a pendulum ("school") clock that are relatively raw. The third image is a cleaned up Timex watch. I didn't run that through a good (e.g, Racal Dana) frequency counter. To reiterate, anything mechanical or even crystal+mechanical is going to need to be cleaned up to get a high resolution frequency readout.The 12F1840 was running at 8 MHz, which gives 500 ns per count. At 32 MHz, the processor "ticks" are 125 ns resolution. That code will run with pretty much any enhanced mid-range PIC. I also used a 16F1829.EDIT: An MCU is not necessary. An early version used a CD4538/14538 monostable in non-retriggerable mode. Adding a comparator to the input gives threshold control. I opted for the MCU to give a digital output.-

author: bdunham7
author_rank: Super Contributor
timestamp: October 22, 2022, 07:46:12 pm
content: Quote from: JTknives on October 22, 2022, 04:26:59 pmSo the biggest obstacle here IMO is getting a relatively clean signal from the tuning fork mechanism. Microphones will be noisy and tapping into the drive coil may be difficult and you don't want to load the circuit and shift its frequency. For a frequency county to work directly and accurately at 300Hz with reasonable gate times, you need very low noise. If I were doing this, I would experiment with getting a decently clean signal that looked stable on a scope however you can and then using a precise signal generator to put a separate trace on the scope at exactly 300Hz, triggering off of this reference signal. Then you observe the watch signal to see if it drifts left or right and adjust it until it doesn't. You would get the precision you need with an observation time of a minute or so.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 22, 2022, 08:20:36 pm
content: A 300 Hz or 1 Hz (tics) signal from the microphone will be quite noise. Good triggering on this is hard and a typical frequency counter will have a hard time.The SW solution with the signal from a sound card can do quite some filtering and looking at the full signal and not just zero crossings (in simpler counters only 1 for start and stop).The weak point with a frequency counter is not so much the clock of timing resolution, but how well the trigger works - with a somewhat noisy and low frequency signal a simple trigger will result in quite some jitter. So time interpolation would be of little use, if the trigger gives more than µs size noise / jitter.A high end (time stamping) counter like the Racal dana can actually gain a little, by looking at most of the zero crossings and not just 2. The signal quality can still be limiting. Chances are the signal from the microphone would be worse than the mains waveform and this is already not easy with a short gate time / aperture time.For the frequency accuracy, just feed a reasonable accurate signal to the soudcard: before / after the test, to a 2nd channel or even superimposed if the SW supports it.Not all sound cards are equally good, but it would at least be worth a try.

author: jpanhalt
author_rank: Super Contributor
timestamp: October 22, 2022, 08:20:52 pm
content: @bdunham7Besides sound, light, and some emitted EMF, how do you detect without interference? Sound will be noisey. What practical alternative do you offer?

author: jpanhalt
author_rank: Super Contributor
timestamp: October 22, 2022, 08:25:05 pm
content: Quote from: Kleinstein on October 22, 2022, 08:20:36 pmPlease give an example of how to do that for this application.

author: bdunham7
author_rank: Super Contributor
timestamp: October 22, 2022, 08:40:18 pm
content: Quote from: jpanhalt on October 22, 2022, 08:20:52 pmI don't have any magic way of acquiring the signal, I think it is going to be noisy no matter what. My visual comparison method will work with even a pretty crappy signal as long as you can see the basic 300Hz in somewhat stable fashion on a display.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 22, 2022, 09:46:05 pm
content: Noise is going to be a problem no matter how you acquire the signal. But unlike listening for a metallic tick, we're looking for a single frequency of 300 Hz. A narrowband active filter is quite reasonable for this application. No, I don't have any schematics.For initial testing at least, delete the reference frequency generator and just use line frequency triggering on the scope. I just tried it and it looks like a frequency resolution of 0.01 Hz is easy. It may not get you to the precise frequency you want, but it cuts out a significant chunk of the hardware necessary to test the total circuit and will get you close enough that only a minor manual tweak will be required.Ed

author: vk6zgo
author_rank: Super Contributor
timestamp: October 23, 2022, 12:09:16 am
content: Quote from: magic on October 22, 2022, 03:22:40 pmIf you have something like a Tek 7000 series analogue Oscilloscope, you have access to the vertical amp signal, & can feed that to arealfrequency counter, in effect, using the huge 'scope as an adjustable Hi Z input buffer amplifier.Sadly, "pretend" Oscilloscopes don't have that facility!------DSOs can get off my lawn!!At the frequencies you are talking about, it wouldn't be hard to make a buffer which could perform a similar function.

author: bdunham7
author_rank: Super Contributor
timestamp: October 23, 2022, 12:38:34 am
content: Quote from: vk6zgo on October 23, 2022, 12:09:16 amThat doesn't get you anywhere, as you will need a relatively clean signal to get a good result from a frequency counter. A very noisy signal that is totally uncountable is still visible on a screen well enough to see if it drifts relative to a reference.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 23, 2022, 02:50:36 am
content: Quote from: bdunham7 on October 23, 2022, 12:38:34 amWith a 7000 series or similar,you can have the signal visible, & if it useable for a counter, have that as well.A "homebrew" buffer can have two outputs, allowing you to do the same thing.One problem is that, if the noise is mains pickup, the 5th or 6th (depending on the Mains Freq) harmonic may well be at a similar level to the desired signal, so there could already be two similar frequency signals drifting w.r.t. each other.The worst thing about trying to answer the original question is that if any of us were "leaning over the OP's shoulder" we could get a handle on how noisy or otherwise the signal is , & choose which method is likely to yield the best results.As it is, everybody has to try to cover all possibilities in their replies.

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 06:10:40 am
content: Well I cobbled this together and I’m going to run it through the computer to see if it will even show up.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 23, 2022, 06:25:42 am
content: Add an equalizer program to your computer and see if you can clean up the signal. One I know of for Windows is Equalizer APO (https://sourceforge.net/projects/equalizerapo/).

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 06:30:10 am
content: Quote from: JTknives on October 23, 2022, 06:10:40 amGood.If it doesn't catch anything, sit the watch on top of the disk. Beware not to apply any mechanical shock while connected to the soundcard. Those disks can generate very high voltage at a mechanical hit.If the signal is not enough, then try a normal microphone, or a mike from a headset, any mic you have around.Once you are able to record the sound, even if it's noisy, we can try to filter out the noise and keep the 300Hz only. Even if it won't be possible to adjust it live, it would be easy to take records of a few minutes then adjust the wristwatch accordingly after each record.

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 06:46:02 am
content: Oh wow, I use used “ soundcard oscilloscope“ and it picks up a very distinct 360Hz

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 06:56:34 am
content: Quote from: JTknives on October 23, 2022, 06:10:40 amAs I wrote above that is what I've been using. The piezo metal disc should be mechanically coupled to the watch body (I soldered a small crocodile clip on the metal part of the piezo disc and I catch it to the crown). I've been using a preamplifier and it works well with Biburo sw. My watch is mechanical one, but your 360Hz buzzing should give you a good signal too.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 06:57:01 am
content: Quote from: JTknives on October 23, 2022, 06:46:02 amVery well!360Hz seems way off, you'll notice the wristwatch running too fast by the minute. Are you shure it should be 300Hz and not 360Hz?Next thing to do is to install Audacity. That will let you record a minute or so, then make the FFT to get a better frequency resolution. It also has filters, so you can filter out anything that is not between 200-400Hz or so.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 06:59:24 am
content: 360Hz is the correct frequency with Accutron watch..

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 07:08:48 am
content: Yeah I misspoke, it’s 360Hz. I added a band pass filter at 350Hz and 370Hz and it cleaned right up.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 07:13:16 am
content: In order to set your watch +/-2secs a day you have to be able to set those 360Hz to +/-0.008Hz..

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 07:20:12 am
content: So I would need a frequency counter?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 07:24:19 am
content: The computer can be a frequency counter, too, but maybe you won't need that at all.The oscilloscope program was good to verify the setup, but that program does the spectrum based on only a few samples. The less samples you have, the less frequency resolution.That is why you'll need a longer record than that oscilloscope program is using. Such a program is Audacity. It's free. Install it and press the record button. Record 1-2 minutes, then press CTRL+A to select the whole record, then make a FFT again with the maximum possible number of samples. You'll get the spectrum with a better resolution.Alternatively, if you are into programming, you can use Octave or Python to write your own FFT and/or filtering.

author: magic
author_rank: Super Contributor
timestamp: October 23, 2022, 07:31:50 am
content: Audacity's frequency analysis is a bit weird, I recall preferring RMAA for some reason, years ago when I was doing something with it.editI see that your scope software has frequency analysis built-in. See if you can increase FFT size to gain more resolution and zoom into the 360Hz region. Increasing FFT size will decrease screen refresh rate, this is normal and it means it's working

author: edpalmer42
author_rank: Super Contributor
timestamp: October 23, 2022, 07:38:14 am
content: That scope display looks really clean. That program is sweet!Try increasing the time control to get more cycles on the screen. Watch the frequency value of 360.02 Hz and see if at some point you get another digit on the frequency. That will give you the .001 Hz resolution that you need.Now adjust your watch for a 360 Hz frequency and see how close it is after a day or two. Tweak the watch as necessary to get it perfect. Now recheck the frequency. You might find that on your soundcard / computer combination the correct reading is actually something like 359.995 Hz. It doesn't really matter what the number is, you just need to know what number to use to get the watch adjusted perfectly. Once you know that number, it shouldn't change unless you change your hardware.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 07:41:30 am
content: There is an open source Time grapher program on github working with sound cardhttps://github.com/vacaboja/tgYou may try to enhance the beats per hour to Accutron value and build it off the sources..Could be an interesting exercise for talented developers..Below a screenshot of freshly installed Tg on Win10 picking up TV news..

author: magic
author_rank: Super Contributor
timestamp: October 23, 2022, 07:44:04 am
content: Quote from: edpalmer42 on October 23, 2022, 07:38:14 amOr change your computer's internal temperatureAll clocks drift, the only question is if the soundcard's clock drifts more or less than your other clocks and whether you will have enough resolution and a stable reference to notice its drift.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 07:58:58 am
content: Adjusting watch of this kind is difficult. Except the temperature the fork frequency depends on the orientation of the fork. Best case you would get +/-10secs/day spread based on the watch orientation (dial up/down, 9up, 6up, 3up) my guess. Thus as with any mechanical watch its accuracy will largely depend on the life style of the wearer..

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 08:11:04 am
content: Man you guys have really tossed me down a rabbit hole.

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 08:17:58 am
content: I tryied that program but it does not like the 360Hz signal. I know with the vintage vibrograf machines you woukd set them to 21600 BPH for tuning fork watches. I tried that setting and it still did not like it. If I could get into the code and change it to see say 1,296,000 BPH then we might get somewhere. I have no idea how the old tube and solid state machines where able to track this watches. It would spit out a ticker tape with a line on it. There is a plastic disk with lines and you line those lines up parallel with the line on the tape. Then read the error on the side of the disk. If the watch is off then the line on the ticker tape is not stright it’s angled.

author: gf
author_rank: Super Contributor
timestamp: October 23, 2022, 08:23:56 am
content: Quote from: magic on October 23, 2022, 07:44:04 amI'd expect that least high-end soundcards have a TCXO or OCXO. Do I expect too much?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 08:49:30 am
content: Quote from: JTknives on October 23, 2022, 08:17:58 amI've just tried and indeed, even when exported as text, Audacity spectrogram is not precise enough, my bad, sorry.Will need something else. The idea is to find something with enough resolution, then calibrate the soundcard+program against the known wristwatch deviation. Once did that, it can be adjusted in minutes instead of days or weeks.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 08:58:18 am
content: Try the Visual Analyser, it claims 0.0001Hz resolution in frequency measurements..https://www.sillanumsoft.org/download.htm

author: gf
author_rank: Super Contributor
timestamp: October 23, 2022, 09:07:51 am
content: Quote from: RoGeorge on October 23, 2022, 08:49:30 amA (say) 0.001 Hz DFT resolution requires to capture 1000 seconds, which are 48,000,000 samples @48kSa/s. The next larger power of two is 2^26 = 67108864 then.Window size seems to be a configurable parameter, but I'm not sure if such a large window size can be entered.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 09:17:30 am
content: See above 360Hz signal from my smartphone via mic into the Visual Analyzer..It does statistics as well..

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 10:05:12 am
content: Hmm, this measurement is more difficult that it seemed at a first look. Maybe curve fitting is the way to go, meaning to record a minute or so, then to try to guess the best sinusoid close to 360Hz that fits those samples, so no FFT.Python has a 'curve_fit' function in the 'optimize' module, though would be nice to find a ready made program that uses curve fit to identify the exact frequency. Random example of curve fitting with Python:https://moorepants.github.io/resonance/03-2020/curve_fitting.html

author: gf
author_rank: Super Contributor
timestamp: October 23, 2022, 11:11:57 am
content: Quote from: RoGeorge on October 23, 2022, 10:05:12 amThere are a couple of ways coming into my mind, e.g.1) Full DFT from a sufficiently large number of samples (1000 seconds, for 1mHz resolution)2) Interpolated DFT from a smaller number of samples (-> zero padding of samples, then FFT)3) Zoom DFT (frequency translate center frequency to DC, low-pass filter and decimate, calculate DFT)4) Zoom DFT with interpolation (with zero padding)5) Zoom DFT calculated via CZT6) Frequency translate center frequency (here 360 Hz) to DC, low-pass filter and decimate, then calculate instantaneous frequency1)Curve fitting is certainly an option too, but I'm not sure if prior bandpass filtering can be renounced.1)see alsohttps://ieeexplore.ieee.org/ielaam/59/8694093/8610231-aam.pdfhttps://wiki.gnuradio.org/index.php/Quadrature_Demod

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 12:41:04 pm
content: By curiosity, I've tried the Lissajous figures method, and a 1mHz is perfectly visible.I've used theSoundcard Oscilloscope programin XY mode (in that progam XY is called X-Y graph). On the channel one it's a 360.001Hz signal from a signal generator, and on the channel two it's the internal generator set at 20x the expected frequency, so 7200Hz (the same program can generate tones and route them to the oscilloscope).The movement is visible even for 1 mili Hertz deviation from 360Hz. The slider called "Scale" (at the bottom of the X-Y graph screen) when dragged to the left can zoom in to see the movement even better.This would be a good start to check how much the real tick is off. Unfortunately the resolution of the generator in this program is only 0.010Hz, could be enough with some fiddling. If my calculations are correct, the declared accuracy of the wristwatch is 0.005Hz, pretty close, the rest can be observed in the speed of the movement, upto 0.001Hz or even 10 times better when zoomed in.That is assuming the soundcard clock is perfect (which is not), but I think this can be calibrated by comparing it with the wristwatch deviation. AFAIK the PC clock has it's own quartz, so the accuracy of the PC's date-time clock doesn't matter, it's only the soundcard's quartz stability that matters. Also, over long time periods, meaning days or weeks, a PC clock that is online has close to zero offset (certainly less than a second), because the OS continuously adjust the time against the available Internet time servers.

author: gf
author_rank: Super Contributor
timestamp: October 23, 2022, 01:16:25 pm
content: Quote from: RoGeorge on October 23, 2022, 12:41:04 pmQuoteIt is actually the frequency of the reference signal which must be accurate.The soundcard clock only matters if the reference signal comes from the sound card, too.If the reference signal is provided externally, then the soundcard clock does not matter too much for x-y mode, since both channels are affected equally.My understanding of the tuning procedure were actually:- connect 360 Hz reference signal (or an integral multiple or fraction) to CH1- connect watch to CH2- adjust the watch until movement stops (then it is also not necessary to quantify the deviation)

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 01:52:14 pm
content: That is the method radio amateurs used to use since ever - they tuned their receiver's VFO with help of the beat with WWV NIST radio transmitters (shortwaves). They did 0.1Hz accuracy at MHz frequencies that way.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 02:21:36 pm
content: Something like that, thought I did slightly different, using the PC soundcard as a reference generator:- connect the 360.xxx Hz from the wristwatch (I've used a Rigol DS4102 generator instead) to the channel 1 (left channel of the soundcard input)- generate with the oscilloscope program 7200Hz to compare against (so the reference here is the PC soundcard, because OP does not have a reference generator) and route this 7200Hz signal to the second channel of the Soundcard Oscilloscope (it has a checkbox in the generator to send the 7200Hz to the second channel)- adjust the wristwatch until there is no movement in the Lissajoux intersections- wait a day, or a week, and see how much the wristwatch deviated (by comparing it with the local radio for the exact time, or another trusted clock)After that, it can be calculated how much deviation to add to the 7200.xx Hz, so to compensate for the observed error, then adjust the wristwatch again. Should work I think, at least in theory.I was curious about the other software that says it can measure with 0.0001Hz resolution,https://www.sillanumsoft.org/download.htmI am using it from Linux, with WineHQ and ALSA sound, not sure if this setup is proper, maybe somebody with Windows and a signal generator can test the same program better, but in my setup it shows a clean 360.000Hz as 360.5yyy where yyy digits are shifting in time, and the distribution seems unusual. I doubt the generator+soundcard will have a 0.5Hz deviation to each other, also I was expecting to see a gaussian shape with the statistics, but the most values are at the extremes values, I don't know why.Most of all it worries me that if I change the generator to 360.001Hz, this frequency meter doesn't detected the 1mHz change.Attaching a printscreen of Visual Analyser (not the oscilloscope program) with the distribution from the high resolution frequency counter against a 360.000_000Hz from DG4102.

author: bdunham7
author_rank: Super Contributor
timestamp: October 23, 2022, 02:23:18 pm
content: Quote from: JTknives on October 23, 2022, 07:20:12 amNo, you would just need a precise 360Hz reference signal to feed to the other channel of your scope. That signal is still pretty noisy, and cleaning it up with filters has its own issues. A frequency counter may struggle a bit to give youa very stable reading. However, it is more than good enough for a visual observation of drift relative to a reference.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 02:29:17 pm
content: Quote from: imo on October 23, 2022, 08:58:18 amThat below measurement was made via mic off my smartphone's speaker as the generator. With a wired connection and a signal generator with optimal amplitude you have to get a much better result, imho..

author: artag
author_rank: Super Contributor
timestamp: October 23, 2022, 02:48:51 pm
content: Quote from: gf on October 23, 2022, 08:23:56 amYes. Only the golden ears brigade 'need' that accuracy of clock.

author: artag
author_rank: Super Contributor
timestamp: October 23, 2022, 02:58:49 pm
content: Quote from: JTknives on October 23, 2022, 08:17:58 amThey worked in the same way as people have suggested using the scope - put a reference signal on the other channel and compare the drift. Imho it's easier to see a small drift like that than with lissajous, which is very dependent on the relative phase (it's easy to see changes at 0 degrees phase shift when you're looking for a diagonal line to thicken, but very hard at 90 degrees when you're looking for a not-quite-circular shape).If you move the paper forward with a synchronous motor at mains rate (or some mechanically geared ratio from it) and put a tick on the paper every time the clock ticks, the tick will make a line when it occurs at the same phase relative to the mains. If a little faster, the tick will occur a little earlier each cycle and the line will drift to the left, etc.The line is recording the difference, not the absolute frequency, and the mains is very stable (or they might have used a good crystal oscillator in countries where the mains is less stable).

author: Transconductance
author_rank: Newbie
timestamp: October 23, 2022, 03:07:03 pm
content: I must be missing something obvious...I agree that you are going to need to use a counter and integrate over a significant amount of time, then compare that to a reference clock.Isn't the watch itself doing exactly this? It's a counter integrating the oscillator frequency over time? Compare the time on the watch to a reference, say a good GPS receiver. Wait 24 hours and compare again.

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 03:11:31 pm
content: I opened two instances of the Visual Analyser - Freq meter and Generator @360Hz - and interconnected them via the Virtual Cable. See below the statistics after 120 measurements..

author: bdunham7
author_rank: Super Contributor
timestamp: October 23, 2022, 03:12:14 pm
content: Quote from: Transconductance on October 23, 2022, 03:07:03 pmSo suppose it takes 15 tweaks to get it just right. Your way would take two weeks, using a process that can be done in under a minute you'll be done in half an hour. Of course you'd want to do what you suggest (once) at the end of the process for verification.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 03:24:05 pm
content: Quote from: imo on October 23, 2022, 02:29:17 pmI suspect the strange results in my case was because of WineHQ, a software that translates Windows calls into Linux calls, so one can run Windows programs under Linux. My setup was with Linux, Kubuntu 22.04 LST + WineHQ + ALSA sound + Rigol DS4102 AWG.Did you used Windows or Linux to run the frequency counter program?

author: iMo
author_rank: Super Contributor
timestamp: October 23, 2022, 03:34:33 pm
content: Yep, I run Win10, see my latest post with two VA instances running..

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2022, 03:49:48 pm
content: Since there is only one soundcard (I guess it's the same card) then the two instances have correlated clocks (same Quartz on the same soundcard) so it is expected to see no variation in the frequency distribution.

author: JTknives
author_rank: Contributor
timestamp: October 23, 2022, 08:02:13 pm
content: This is a much nicer program. Ran a different accutron on it for 3hrs and it looks great. I need to build a better pick up setup but this got me started.

author: edpalmer42
author_rank: Super Contributor
timestamp: October 23, 2022, 08:56:23 pm
content: There's a 4-part video on Youtube about the Accutron with an experienced teacher and repair tech. He says that the watch will gain or lose 4.5 seconds per day depending on the orientation. That works out to 0.019 Hz on your 360 Hz signal. He says to set the watch 2 sec. per day slow so that it averages out to be more or less correct in use.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 24, 2022, 06:49:43 am
content: Quote from: JTknives on October 23, 2022, 08:02:13 pmGlad to hear it almost work. Maybe sit the watch on the piezo disk, or maybe make a stack with 3-5 piezo disks in series, or maybe use a normal microphone instead? Either way, please keep us updated.Quote from: edpalmer42 on October 23, 2022, 08:56:23 pmWhich one? There are many Accutron videos, but none that I found have 4 parts. Could only found something that has part 3. I didn't know how Accutron works. This video explains it:Quartz movements - Part 3of3 (plus Tuningfork Bulova Accutron)Very clever and efficient design!Later edit:It's even more interesting than it first seemed to be, the ratcheting mechanism hasno teethmicroscopic teeth!https://youtu.be/gqU2iX-sQEo?t=890

author: Kleinstein
author_rank: Super Contributor
timestamp: October 24, 2022, 08:13:53 am
content: Quote from: gf on October 23, 2022, 11:11:57 amCurve fitting is an option, though it need some time. With a reasonable starting point for the frequency, there is no need for prior filtering.The quadrature demodulator or hilbert transformation is a nice way: one gets a local (e.g. a few periods) phase and than gets the frequency as the linear slope of the phase. The DFT can also use the IQ data and this way can work near zero frequency, as with complex data to start with one gets positve and negative frequencies.

author: richnormand
author_rank: Unknown
timestamp: October 24, 2022, 06:47:47 pm
content: Have a look at page 2 of this thread:https://www.eevblog.com/forum/blog/eevblog-920-world_s-first-transistor-watch!/25/Just a coil and a preamp.That was then. Today I have a 12 digit counter and a GPSO setup that can do a lot better.Nice piece of history that I wear several time a year.Cannot leave the watch on the bedroom wood desk, the resonance hum wakes me up!

author: RoGeorge
author_rank: Super Contributor
timestamp: October 24, 2022, 07:03:17 pm
content: Doh, so the ratcheting wheel does have teeth after all?!

author: edpalmer42
author_rank: Super Contributor
timestamp: October 24, 2022, 07:29:20 pm
content: Quote from: RoGeorge on October 24, 2022, 06:49:43 amGo here:https://www.youtube.com/channel/UCuSoVt0NSplcHOcfFX40D2A/videosScroll to the bottom. The four videos at the bottom of the list are the ones. Part 4 includes a section on how to regulate the watch.Ed

author: SpecialK
author_rank: Regular Contributor
timestamp: October 24, 2022, 09:29:52 pm
content: https://youtu.be/5n791JAVpv0?t=382

author: mwb1100
author_rank: Frequent Contributor
timestamp: October 24, 2022, 10:16:32 pm
content: Apologies for the somewhat off topic post: As a novice in electronics I almost skipped this thread when I saw the subject line - but that would have been a huge mistake. Pretty much all the stuff about how to do the measurements is waaayyy above my head, but the information on the Accutron is just sensational! I'm going to have to watch all these videos over the weekend.Many thanks to everyone involved.

author: JTknives
author_rank: Contributor
timestamp: October 25, 2022, 02:23:42 am
content: Ok so after trying a larger piezo and not having any better luck I thought I would try this. I took a spare coil and soldered the mic cable onto it. These coils are rare and very delicate. Thy are wound with .015mm wire and enough of it to make about 5.7 ohms. So I think this is working rather well. I don’t know if the added load on the fork magnet from the extra pickup coil is enough to affect it but the results seam great. But then it got me wondering if I could just tie into the pickup coil in the watch? The coil that drives the transistor without affecting the Hz.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 25, 2022, 06:54:12 am
content: I don't think the statistics should have two peaks at the extreme.My guess is there are now two peaks in the measured frequency distribution because the measuring coil is influencing the oscillator. With the piezo disk it used to be a single hump in the middle, which was closer with an expected Gaussian distribution in its shape. Or maybe you changed the two adjustments on the tuning fork, and now there are two resonant frequencies in the tuning forkDo you have 2 desktops or 2 laptops? If yes, try measuring with both at the same time, one with the coil and one with the disk, then compare the results. If the one with the piezo also shows two peaks only when the measuring coil is nearby, it means the coil influences the oscillator.Direct electric contact will certainly influence the oscillator, though no idea by how much. I would avoid doing that.

author: JTknives
author_rank: Contributor
timestamp: October 25, 2022, 08:18:18 am
content: Yeah I noticed the valley in the graph and was perplexed. I’m wondering if it’s picking up both magnets weirdly. I’m currently doing another test with a very tiny microphone from a wired ear bud. I just removed the board from the lapel clip and soldered it to my mic wire. It’s looking promising with a band pass filter of 355Hz-365Hz