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I used pulsar detection techniques to turn a phone into a watch timegrapher

chronolog.watch

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Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#11

Post by mkesper »

tylerjaywood wrote: post #2

I built an audio timegrapher feature for my watch accuracy app, ChronoLog. Professional timegraphers use a piezo contact sensor and can cost upwards of $1,000. I wanted to do it with a phone mic. The problem: an iPhone's built-in microphone picks up a mechanical watch's tick at about 1.5 dB SNR. The solution turned out to be epoch folding — the same technique radio astronomers use to find pulsars. Stack 100+ tick per…

Awesome writeup! I wonder whether with a real contact mic (Korg offers one for about 20 bucks) you could get much better results. Due to no 3,5mm on phones anymore it might be easier to use a sound-enabled SBC though.

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#12

Post by matheusmoreira »

fred_is_fred wrote: post #8

This is a fascinating read but what do you do with this information? Is there a threshold at which you need to take the watch apart and fix something or is this just useful info to know about your watch?

It tells you for how long the time displayed by the watch is valid. If a watch loses ten seconds per day, in a month it will be about five minutes off.

The objective is to minimize this number as much as possible. The open source sensor watch has a temperature sensor and software which turns it into a temperature compensated quartz watch. Mine loses time every year instead of every day or every month.

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#13

Post by pastescreenshot »

fred_is_fred wrote: post #8

This is a fascinating read but what do you do with this information? Is there a threshold at which you need to take the watch apart and fix something or is this just useful info to know about your watch?

It is actually pretty useful if you own a few mechanical watches. Daily rate tells you how annoying the drift will be, beat error can hint that regulation or service is due, and measuring in different positions gives you a decent sanity check on movement health. Even if you never open the watch yourself, it is a much better baseline before taking it to a watchmaker.

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#15

Post by coredog64 »

matheusmoreira wrote: post #12
fred_is_fred wrote: post #8

This is a fascinating read but what do you do with this information? Is there a threshold at which you need to take the watch apart and fix something or is this just useful info to know about your watch?

It tells you for how long the time displayed by the watch is valid. If a watch loses ten seconds per day, in a month it will be about five minutes off. The objective is to minimize this number as much as possible. The open source sensor watch has a temperature sensor and software which turns it into a temperature compensated quartz watch. Mine loses time every year instead of every day or every month.

Practically speaking, unless you only own a single mechanical watch you really only care about the per day loss.

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#16

Post by adrian_b »

fred_is_fred wrote: post #8

This is a fascinating read but what do you do with this information? Is there a threshold at which you need to take the watch apart and fix something or is this just useful info to know about your watch?

Old mechanical watches and clocks had an adjustment with which you could change slightly the oscillation frequency of the balance wheel (usually by changing the tension of the balance spring).

You used a device like that described in the parent article to measure the deviation from the correct frequency and you adjusted the frequency with a fine screwdriver or a similar tool, until measuring the desired nominal frequency.

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#17

Post by tylerjaywood »

CamelCaseCondo wrote: post #9
tylerjaywood wrote: post #2

I built an audio timegrapher feature for my watch accuracy app, ChronoLog. Professional timegraphers use a piezo contact sensor and can cost upwards of $1,000. I wanted to do it with a phone mic. The problem: an iPhone's built-in microphone picks up a mechanical watch's tick at about 1.5 dB SNR. The solution turned out to be epoch folding — the same technique radio astronomers use to find pulsars. Stack 100+ tick per…

If you know the structure of the “tick”, you can apply the technique of a correlation receiver. It can dig up signals below the noise floor and is used in GPS reception.

I'll do some research on this! I have a nagging feeling that there is more I can do to get the most out of this, but struggle with knowing where to look since this is not my background. I'm learning a lot as I go!

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#18

Post by tylerjaywood »

mkesper wrote: post #11
tylerjaywood wrote: post #2

I built an audio timegrapher feature for my watch accuracy app, ChronoLog. Professional timegraphers use a piezo contact sensor and can cost upwards of $1,000. I wanted to do it with a phone mic. The problem: an iPhone's built-in microphone picks up a mechanical watch's tick at about 1.5 dB SNR. The solution turned out to be epoch folding — the same technique radio astronomers use to find pulsars. Stack 100+ tick per…

Awesome writeup! I wonder whether with a real contact mic (Korg offers one for about 20 bucks) you could get much better results. Due to no 3,5mm on phones anymore it might be easier to use a sound-enabled SBC though.

This is definitely the way. Even the old wired mics Apple phones used to ship with that had the little rectangle mic works better because you can press it right up against the case back.

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#19

Post by myself248 »

coredog64 wrote: post #15
matheusmoreira wrote: post #12

Earlier quoted context omitted.

It tells you for how long the time displayed by the watch is valid. If a watch loses ten seconds per day, in a month it will be about five minutes off. The objective is to minimize this number as much as possible. The open source sensor watch has a temperature sensor and software which turns it into a temperature compensated quartz watch. Mine loses time every year instead of every day or every month.

Practically speaking, unless you only own a single mechanical watch you really only care about the per day loss.

You know what they say. Man with one clock, always knows what time it is.

Man with two clocks, never quite sure...

Re: I used pulsar detection techniques to turn a phone into a watch timegrapher

#20

Post by tylerjaywood »

TApplencourt wrote: post #3
tylerjaywood wrote: post #2

I built an audio timegrapher feature for my watch accuracy app, ChronoLog. Professional timegraphers use a piezo contact sensor and can cost upwards of $1,000. I wanted to do it with a phone mic. The problem: an iPhone's built-in microphone picks up a mechanical watch's tick at about 1.5 dB SNR. The solution turned out to be epoch folding — the same technique radio astronomers use to find pulsars. Stack 100+ tick per…

How does it compare to other apps ("watch accuracy meter" for example) on android?

I have this in open beta on Android right now so you're welcome to give it a shot and let me know :)

One difference is cost. I know that mine is lower cost, and is a one time unlock -- no subscription. So there's that. I'm also therefore positioned a little bit more towards the casual user, I prioritize speed of completion which means I need high confidence in a good signal quickly and don't hesitate to cancel mid-flow.

I think one thing alternatives offer is the ability to run for longer -- like a 10 minute check for instance. There are marginal gains in precision for every additional second, but they seem to diminish pretty quickly past 30 secs or so. But that's one difference I'm aware of.

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