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Not sure if this link has been posted before but just in-case for those that are following this thread some views of the inside (including mic) of a commercial machine, the mic looks to use one of the thin piezo vibration transducers with a built in pre-amp, the TLO71 is essentially identical to a TLO72 but is single rather than dual.

https://www.eevblog.com/forum/reviews/weishi-mtg-3000-'multi-function-timegrapher'/

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I'm a watch DIYer, having serviced two watches myself, partially using tools of my own making. One thing I've been working on over the last few months is my own PC based timing machine. I've finally g

So I played a bit in Solidworks, and this is what I got. A friend of mine helped me with the 3D printing.   sup_2.STL mic 2.STL pesa.STL sup_1.STL   the

Dear svorkoetter, These days with my failing eyes and ears I have given up working on watches and confine myself to pocket watches and clocks. I find that I can deal with the larger components easier

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By the way svorkoetter I take my hat off to you for this post and the great work on the timegrapher, my original training was in electronics and now retired I service/repair/rebuild tube amps on the side, I have scratch built quite a few bits of gear over years and know full well the toll it places on your time, keep up the good work. I have everything needed to knock up a mic and preamp in my junk/spare parts bin so will give it go.

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Just want to thank all of you, especially@svorkoetter, for this diy timegrapher.

Finally finished my amplifier combining the circuit of@svorkoetter and@wlysenko. But I have to read on all the replies to gather all the lessons learned and best practices. Hats off to all of you who contributed to this post.

Now, on to improving the sensor part...

Happy New Year!

 

2a8d261913d94ba3929ba30060bef6ae.jpg

Sent from my ASUS_Z010D using Tapatalk
 

Edited by joelcarvajal
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P.s. you need:

a metric 6, long screw (with 10mm hexagonal head at one end and only a couple of centemeters of thread at the other - the rest, in between, should be smooth)

4 metric 4 screws

A spring

a metric 6 nut

A 35mm diameter piezo

Mono shielded cable 25cm long

3.5mm jack (depend8ng on your amp)

 

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Do we really need a mic pre-amp these days? I can understand that back when you needed a sound card (and set the port address with DIL switches lol), but modern PC's and Laptops should be fine with a mic connected directly.

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2 hours ago, p2n said:

Do we really need a mic pre-amp these days? I can understand that back when you needed a sound card (and set the port address with DIL switches lol), but modern PC's and Laptops should be fine with a mic connected directly.

Yes. A piezo microphone produces a much lower signal level than a condenser mic, on the order of microvolts. Very few sound cards work with such low levels, even if they have a dedicated mic input (which most laptop sound card inputs actually are). Some amount of amplification is needed for a mic input, and even more for a line level input.

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I did a quick try on the PC and I was clipping with no pre-amp.

Want to use WOS on the laptop though which has no mic (or line) inputs. Does WOS work ok with USB microphones?

 

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Are you sure you were using a piezo mic? If a piezo mic clips on your PC's input, a regular mic would blow up the computer. :biggrin:

Yes, WOS will work with USB audio devices. If the device is visible to Windows, WOS can use it.

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16 minutes ago, svorkoetter said:

Are you sure you were using a piezo mic? If a piezo mic clips on your PC's input, a regular mic would blow up the computer. :biggrin:

Yes, WOS will work with USB audio devices. If the device is visible to Windows, WOS can use it.

No microphone will blow up a PC mic input.

As for this one - considering the price I'd imagine it was a piezo - it's a £9.99 lapel mic. It's in a USB mic adapter at the mo and the gain is very low, but seems to work ok.

When I fire up the PC next I'll post the trace on that with the same mic but using the MIC in (realtek sound built into mother board).

 

 

wos_trace.JPG

wos_trace2.JPG

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56 minutes ago, p2n said:

No microphone will blow up a PC mic input.

Hence the smiley in my post.

56 minutes ago, p2n said:

As for this one - considering the price I'd imagine it was a piezo - it's a £9.99 lapel mic.

If it's a lapel mic, it's not a piezo. It's an electret condenser mic. These have a built-in preamp. We tend to avoid those because they have DC current running through them, and could, in theory, magnetize your watch.

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6 minutes ago, svorkoetter said:

If it's a lapel mic, it's not a piezo. It's an electret condenser mic. These have a built-in preamp. We tend to avoid those because they have DC current running through them, and could, in theory, magnetize your watch.

That's a really interesting point! I'll see if I can detect any magnetic field... <rushes off to find the compass>.

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34 minutes ago, svorkoetter said:

We tend to avoid those because they have DC current running through them, and could, in theory, magnetize your watch.

I don't think I've ever heard that reason before?

The capacitive microphone circuitry requires very little power is usually an FET specially designed for this.

We're dealing with an interesting problem we want to pick up the vibration of the watch not necessarily the audio sound. Ideally we want no sound at all like the noise around the room the fan in the computer etc. Then yes for those nitpicky people sound is a vibration. Capacitive microphones work great for sound not the best for vibration. For vibration piezo works great and unfortunately it also works good as an audio pickup. So it becomes an interesting challenge to build a pickup device to pick up the vibration of the watch has sufficient sensitivity but not pick up everything around it including the vibrations going through the cable like if you touch the microphone cable. This happens on clock pickups you grab the cable and you can hear that.

 

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10 hours ago, JohnR725 said:

So it becomes an interesting challenge to build a pickup device to pick up the vibration of the watch has sufficient sensitivity but not pick up everything around it including the vibrations going through the cable like if you touch the microphone cable.

What you want then is a pin attached to the microphone diaphragm. The diaphragm can be covered to exclude unwanted noise and the pin can extend out of the cover and contact the watch directly.

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An actual vibration sensor, as discussed somewhere earlier in this thread, and of which I've ordered some but not yet used, would probably work even better. Guido, I wonder if your sensor would be improved by cutting down the piezo disc into just a strip?

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Another idea that I have not been able to prove due to our limited access to technology is a piezoelectric "bimorf" sensor. According to the specifications it is much more sensitive than a piezo electric disk, and I can see that it is less prone to pick up the noise from the 60 or 50 Hz electrical network. This is it. I would like if somebody can verify it, that we share here the resusltados, building a microphone from this device.   https://uk.rs-online.com/web/p/vibration-sensors/0285784/

Éxito!

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