Tick Tock timing application

PhilHornby

Senior Member
You are over thinking this. A piezo disc will output over 90 volts if tapped directly. No amplication is required, indeed, you need to protect the ADC input with clipping diodes, but that is all that is required.

A microphone detects acceleration, which is what you have. A jerk detector detects changes in acceleration, which is what you want. NOT when a tik or tok occurs, but the difference between them from an arbitrary zero point.
Interestingly, though I have read about these super high voltages, I cannot induce one. The highest I've seen is about 20V ish - and that involved a heavy impact. (As measured with 'recording' DMM and 'scope).

I found a 'patent' for a 'Sensor for measuring jerk'. It's quite an interesting insight, but the application seems to be more about measuring changes in already moving things (worn bearings etc). If I hadn't seen your video, I would probably have intuitively guessed that it wouldn't work in a clock application...

Anyway, I built said "Jerk Detector" - (more-or-less) as instructed :-

24990

With a 'cased' Piezo Sounder connected to one Scope input and the contraption above plugged into the other, I compared responses.

The Jerk Sensor was (almost) impervious to sound (apart from the loudest of handclaps) and produced a much larger signal than the 'cased' Sounder, in response to tapping the desk. The latter - while very insensitive, did respond to sound (handclaps, whistles etc).

I took my 'Scope to the clock (since I didn't want to disturb it) but wasn't able to pick up a usable signal from either unamplified Piezo :(

(This wasn't helped by the presence of an unwanted signal being received in the region of the clock! I thought it was perhaps a nearby zigbee Radiator valve, but disconnecting it made no difference. Very odd that the Jerk Sensor picked this up, but not the 'cased' Sounder (which just had some mains hum) - could just be a difference in scope probes I suppose ... or the excessively long leads :whistle:).
 
Last edited:

PhilHornby

Senior Member
The 'Jerk Sensor' and Amplifier combination works better than the 'cased' Sounder + Amplifier :-


Sorry about the heavy breathing :D
 

rq3

Senior Member
The 'Jerk Sensor' and Amplifier combination works better than the 'cased' Sounder + Amplifier :-


Sorry about the heavy breathing :D
Very nice! I was shocked what a difference it made adhering a mass to the piezo disc. And it certainly sounds like your clock is "in beat"!
My only thoughts are that it's important not to restrain the piezo disc by clamping its edges. Just lightly glued or resting on a three point support will allow the entire piezo assembly, mass and all, to move "en mass" to microphonics, so there is negligable response other than to an actual change in acceleration.

And the central mass should ideally be a sphere, with minimal contact area to the piezo itself. Otherwise, it damps the disc reponse having adhesive goobered all over the surface.

Your clock audibly sounds very nice, and what a great way to learn about its quirks and foibles! They are truly works of art. I've been working on building a Macdowall (one of your fascinating compatriots) escapement clock for many years, and hope to have the prototype running soon. There are references to the Macdowall escapement actually having been used in portable watches, but for the life of me can't figure out how that would work.

In any case (whether long or pocket, pardon the pun), the Macdowall always struck me as the most mechanically elegant device, having only one moving part, but requiring an extra gear train due to it's very rapid advance.

As I mentioned, I would be happy to mail you one of my complete sensors. I use one on my 3D printer as a leveling detector, and it works shockingly well. In fact, I did ship two of them to a gentleman in England, who has been instrumental in the 3D printing community for many years, and would be happy to do the same for you, but obviously don't want to get inundated with "me too" requests. Shoot me a PM if interested. No charge, consider the offer an early Christmas present in these trying times, and an appreciation for all that you have contributed to this forum over the years.
 
Last edited:

PhilHornby

Senior Member
Your clock audibly sounds very nice, and what a great way to learn about its quirks and foibles! They are truly works of art.
That 'Cuckoo clock' Android app. seems to have done the trick :)

At some stage, I want to see if I can improve its timekeeping electronically - but with the least possible interference (some sort of solenoid to 'catch' the pendulum and hold it in place for a seconds or two maybe?) . Still thinking about that one!
I realise there are many methods already out there, but 'catching the pendulum' would require the most precise timing - which appeals :)

I've been working on building a Macdowall (one of your fascinating compatriots) escapement clock for many years, and hope to have the prototype running soon.
I'd never heard of Charles McDowell of Wakefield and you'd have thought I might have. Wakefield is where I'm from!
John Harrison (of 'Longitude Prize' fame) was also from Wakefield and I'd never heard of him either, until they made a film about the events.
 
Top