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Old 11th Nov 2022, 10:58 pm   #1
Uncle Bulgaria
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Default Piezo element?

This is from the microphone attached to one of my watch timing machines. Is it a form of piezo crystal? The rubber sleeve bottom right isolates a crocodile clip from the casing. The clip is to be attached to a clock movement, and the output screened cable goes to the ECC83 circuit attached.

What could I replace it with? This one has been in the wars!
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Old 12th Nov 2022, 5:57 am   #2
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Default Re: Piezo element?

The first thing I'd be inclined to try is one of those piezo buzzer disks of a suitable diameter. They certainly will work as sensors and you might get enough signal from it.
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Old 12th Nov 2022, 2:37 pm   #3
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Default Re: Piezo element?

Thank you Tony. I was struggling to find anything small enough! I have one of the circular ones at about 50mm in my parts box, and see eBay goes down to perhaps 15mm which is still too big. The original piece is rectangular, from what I can see beyond the corrosion, and they seem to be a rara avis.

Farnell does list one circular one, called a '9.5kHz sounder', in stock at 12mm diameter which may just fit. However, I'll need to bulk out the order a bit...

Some of the larger stand microphones used with a watch clipped between spring-loaded supports have a similar problem of no output, and corroded elements. However, with a bit more room in the body it's possible an available type of circular element will fit.

I'm surprised a single ECC83 is enough to amplify these signals. With the one microphone that seems to provide an output, I have to have the gain near full to distinguish the ticking on an earphone, and the drive doesn't seem to be enough to reliably fire the solenoid on the ticking.
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Old 12th Nov 2022, 4:08 pm   #4
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Default Re: Piezo element?

Have you considered an electret mic element? They are very small dia, although not so thin of course, and cheap. Some do not even require much in the way of polarising voltage if any.
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Old 14th Nov 2022, 11:18 am   #5
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Default Re: Piezo element?

I made a timegrapher 'mic' around a year and a half or so ago, I used a piezo element the kind commonly sold as a violin pickup, I believe they also double as mini beepers/speakers, I made a post about it - I'm reposting the pics here. In a nutshell I superglued the element to a 5mm pitch screw head that had been filed flat, this was then bolted to the metal clamp/sound pick up by the nut I think the pics explain it better than I can, it works very well, I use mine with the free version of watch o scope installed on my pc.
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Old 14th Nov 2022, 11:55 am   #6
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Default Re: Piezo element?

Or could you even use a ceramic PU cartridge?
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Old 14th Nov 2022, 11:56 am   #7
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Default Re: Piezo element?

retailer's original thread here: https://www.vintage-radio.net/forum/...d.php?t=176686
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Old 16th Nov 2022, 1:21 pm   #8
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Default Re: Piezo element?

Would a crystal earpiece yield a suitable piezoelectric sensor?

Regards,
Symon
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Old 16th Nov 2022, 4:24 pm   #9
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Default Re: Piezo element?

Thanks all - I hadn't tried the phrase 'timegrapher' in my searches. An informative thread, and a good result retailer! Those are the same type of elements that I'm looking at as they're widely available. I guess the original in my photograph is a proprietary early '60s rectangular type (with associated very compliant copper foil flying leads).

A crystal earpiece is probably the same sort of thing. I haven't got one to hand to check, but it could be that the larger diameter of the exterior holds the same kind of piezo that would be too large to fit in the clip-on housing.

I'm going to try some of the CPC 12mm elements as I've got enough other things to make up the minimum order, so I can experiment.
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Old 16th Nov 2022, 4:42 pm   #10
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Default Re: Piezo element?

Maybe you could also consider an 'electret' mic insert [as fitted to both landline and mobile telephones since the 1980s] with a suitable bias-battery?

There again, it's amazing the output of some piezo transducers: a friend's bathroom-scales use four of them. Not only do they sense the avoirdupois of the person standing on the scales, but they generate enough voltage to power the scales. There's no battery, you just tap the platen on top of the scales a few times to wake them up, then you climb on board and the energy of your wakeup-knocking powers the LCD and its associated microprocessorage for long enough to tell you just how overweight you are.
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Old 16th Nov 2022, 4:49 pm   #11
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Default Re: Piezo element?

I'd be surprised if there's anything wrong with the actual ceramic element - it is ceramic after all, which is robust so long as you don't smash it! From your photo, the element looks intact, but the metal foil contacts (which should be clamped on to it) look like a disaster area.

The only relevant experience I can offer is gained from repairing an early 1950s EMI 'double-C' ceramic pickup head, probably of similar age to your sensor, which had similarly mangled foil contacts. In that case I found that the areas of the element which are supposed to contact the foil were copper plated and, to my pleasant surprise, I found it possible to quickly solder thin flexible connecting wires to the copper plated areas. That proved a much better connection than the original foil, and the pickup has continued to work ever since. Has your element got copper plated areas that you could solder to? - I fancy I can see some copper plate, but I may be mistaken.

Hope that helps.

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Old 16th Nov 2022, 6:06 pm   #12
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Default Re: Piezo element?

Hi UB,
did you find these site please _need lot of time to read it, but has good results: https://www.watchrepairtalk.com/topi...e/17/#comments and .../page/51/#comments tooo
K.
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Old 26th Nov 2022, 6:49 pm   #13
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Default Re: Piezo element?

Thank you, karesz* - a very interesting discussion! I was particularly interested by the first picture attached, which shows the interior of a Greiner microphone unit, and here's the link to the RS vibration sensor the poster thought was similar.

I happen to have one of the same models of microphone, and on taking it apart (second picture) see it's suffered the same fate as the one I opened this thread with: the encapsulation of the sensor has completely disintegrated. Interestingly, the exposed contact is the same shape as the RS part, but obviously used to be part of a larger square unit glued to the bar that passes through the casing to become the clip that holds the movement.

I've received some standard small disc piezo transducers which I will try. Does anyone have any soldering tips for these, apart from very flexible wire? One to the brassy disc and one to the smaller silver one, with one side bonded to the clip?
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Old 26th Nov 2022, 7:51 pm   #14
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Default Re: Piezo element?

It might be a typo or mistranslation I can't fathom, or is it some technique I've never heard of ?.

The last line of the RS vibration sensor description says :

"A vibration sensor can also be used to determine aromas in the air by simultaneously measuring resonance and capacitance."

?.

https://uk.rs-online.com/web/p/vibra...ensors/0285784

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Old 26th Nov 2022, 9:35 pm   #15
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Default Re: Piezo element?

Hi all, a few years ago I built a watch timer from the watch-o-scope site. it uses a ceramic disc sounder feeding a tl074 quad op amp. it uses the pc sound card for timing, remarkably stable. one awkward bit was mounting the ceramic disc, poundland came to the rescue with selfie stick (no kidding) the sprung part holds the watch perfectly. Peter
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Old 26th Nov 2022, 9:46 pm   #16
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Default Re: Piezo element?

Thanks, but I have a number of legit Greiner microphone units that I am putting into service. I've just epoxied one of the little piezo elements to the clip in the opening post, so when that sets I'll report on output...
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Old 7th Dec 2022, 1:06 pm   #17
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Default Re: Piezo element?

The clip in the opening post now has a piezo attached and ticking is audible through the earphone when it's clipped to a small wristwatch. The solenoid plate in my waxie-free unit appears to bang in time with this ticking, but only when the gain is increased significantly with the appropriate knob. I guess the piezo has quite a low output, and solenoid firing is intermittent with a new piezo in the microphone unit shown in post #13.

I guess my next step is to try one of the 'vibration sensors' from the RS link, and then perhaps investigate inserting a solid-state preamp stage to the microphone input.

The timing unit is well shielded - hum is heavy with the lower grille removed for access to the circuitry and chassis, but with it in place it's very quiet even at full volume. I'm impressed when it's only a piezo signal going into an ECC83 in the same chassis as the mains supply with plenty of opportunity for interference.
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Old 13th Dec 2022, 9:19 pm   #18
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Default Re: Piezo element?

Quote:
Originally Posted by Buzby123 View Post
It might be a typo or mistranslation I can't fathom, or is it some technique I've never heard of ?.

The last line of the RS vibration sensor description says :

"A vibration sensor can also be used to determine aromas in the air by simultaneously measuring resonance and capacitance."

?.

https://uk.rs-online.com/web/p/vibra...ensors/0285784
Well, people often talk about sound being "coloured", a euphemism for "distorted" in my book.
Then there is the medical condition called Synesthesia, but in all honesty aromas is likely to be a literal translation from the original manufacturers data sheet. Japanese can be a very poetical language.
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Old 14th Dec 2022, 12:20 pm   #19
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Default Re: Piezo element?

Try substituting "vapours" or "pollution" perhaps for "aromas"?

Anything untoward in the air will affect the air's physical properties like permittivity which could presumably be sensed by changes in the element's resonant frequency.
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