Fine tuning an old church clock

Greetings!

I am the curator of my local church clock, an unusual example of a four face clock on a rural Essex church (most do not have a face pointing over the nave). The clock itself was installed when the tower was rebuilt in the mid 19th century, but as everything about the installation is cack-handed, I suspect the mechanism was not new at that time.

If anyone has ever played with a grandfather clock, the mechanism is broadly similar, but with every dimension scaled up about six fold.

It keeps reasonably good time, but the lever that trips the chiming mechanism is only consistent to about +/- ten seconds each hour.

This lever is lifted by a cam, first to prime the mechanism at about three minutes to the hour, and then initiate the chiming sequence on the hour itself. From initiation to actually ringing the bell takes about 3.5 seconds.

My idea is to run the clock very slightly slow, and then introduce a precisely timed actuator to nudge this lever so that it chimes precisely on time each hour.

The mechanics of making the actuator are not a huge challenge. I plan to use a small pneumatic ram, powered by a small 12V compressor of the type used to inflate car tyres. The compressor will need a few seconds to power up, so I plan to take a pulse from a timing device and use that to fire up both the compressor and a simple 555 based timer which will also fine tune the chime timing.

What I need therefore is a precise pulse to come in at 59 minutes and 50 seconds of each hour.

I've read up about the NPL 60KHz atomic time signal, but I note comments about it's unreliability and susceptibility to interference.

GPS seems more promising, but unless I've been looking in the wrong places, a module that can interface with an Arduino seems hard to find.

The Arduino technology I understand in principle, but have not played with in practice.

Can anyone point me to a device or module that can pick up the GPS time signal, and deliver it to an Arduino board in a manner that can be decoded?

Ten seconds an hour “ scatter” seems pretty good to me,

But ...
If the clock is drifting out ( and that’s what you mean ) eg running slow or fast , then compensating that by adjusting the timing of the pendulum , by reference to an accurate clock is the way to go . You can influence the pendulum with electromagnets

Search for NEO-6m. You'll likely need the tinyGPS library.

One thing to beware of is that GPS needs a good view of the sky. You may not get any signal at all inside the tower.

“If the clock is drifting out ( and that’s what you mean ) eg running slow or fast , then compensating that by adjusting the timing of the pendulum , by reference to an accurate clock is the way to go . You can influence the pendulum with electromagnets”

The clock is endlessly drifting! - it is very temperature sensitive in that regard. I keep it adjusted with old pennies stacked on the pendulum bob, however my objective here is deal with the ‘scatter’ as you call it.

“Search for NEO-6m. You’ll likely need the tinyGPS library”

Thanks - will check that out.

“One thing to beware of is that GPS needs a good view of the sky. You may not get any signal at all inside the tower”

There are big leaded windows in the room where the clock sits. I know that small panes can sometimes create havoc with mobile phone signals, so if that’s a problem I’ll use the room above where the bells are, as that room has wooden louvres, with loads of gaps where I could stick something outside if necessary.

  • Thanks for the fast responses!

Instead of GPS, are you within range of a WiFi signal to access an NTP server?

Thee is no need for a 555 time, the arduino can handle all the timing and control functions.

The clock is endlessly drifting! - it is very temperature sensitive in that regard. I keep it adjusted with old pennies stacked on the pendulum bob, however my objective here is deal with the 'scatter' as you call it.

I've heard the same technique is used to adjust Big Ben, probably very common on large pendulum clocks. A mechanism to automatically place/remove small weights from the pendulum might be an interesting project.

Rather than use electricity to compress air and use an electric valve to actuate a pneumatic cylinder, why not use an electric actuator? How much force is needed? Maybe something as simple as a hobby servo would be sufficient.

Just out of pure curiosity and nothing to do with your immediate problem, but how do you adjust these tower clocks for day light saving time, in your case British Summer Time ?

With any design like this, you should always have a path back to the original so that, if anything goes wrong with your add-on, you (or any successor of yours) can easily restore the original functionality.

With GPS modules you can get an active antenna with some meters of cable. E.g. 1pc GPS Active Antenna Aerial MCX Male Plug Connector Adapter Cable 3m/9Feet New | eBay . Ensure it is compatible with your module.

There are 2 issues in that clockwork.

  1. The Clock doesn't keep the speed well enough.
  2. The start of chimes is a bit shaky.

I my opinion the chime must be well syncronized to the clock, the minute pointer. Else You will some kind of ghost chiming. I guess it is possible to hold the chime on wait but is it possible to fire the chime if the clockwork mechanism has not reached the point of firing?

Keeping the speed of the clockwork is the second task to take care of. How to introduce a mechanicly adjusting electronic device will be delicate. Regarding GPS, just get a NEO-6M with the 1x1 inch antenna and check. My one works indoors, covered by a foot of concrete.

Big Ben was mentioned. Have You thought about asking the Big Ben Service Guys for their opinion?

A simple DS3231 RTC module could improve your 10 seconds per hour, to about 10 seconds per 6 months. Wouldn't that be good enough?

Am I a luddite for thinking it is a shame to introduce electronics into an antique clock?

Mr Harrison was able to make very accurate clocks long before electronics appeared on the scene.

...R

Robin2:
Am I a luddite for thinking it is a shame to introduce electronics into an antique clock?

Mr Harrison was able to make very accurate clocks long before electronics appeared on the scene.

...R

No, but it is probably hard to find someone with the skill set for that now, kind of like steam locomotive engineers or maintainers.

I think a non-invasive solution would pay the most respect to the device. It would be a shame to make the clock unusable without electronics.

Robin2:
Am I a luddite for thinking it is a shame to introduce electronics into an antique clock?

Mr Harrison was able to make very accurate clocks long before electronics appeared on the scene.

...R

Especially when you're only talking about ten seconds. What a wonder of engineering that does that totally mechanically. A real shame in my eyes.

I'd suspect the fluctuation in the chime mechanism is caused by a combination of friction and sloppy gearing (due to wear over the years). The weather conditions also probably have an effect on the force the cam needs to exert on the lever.

If the cam is lifting the lever to prime the chime mechanism, then allowing it to fall to set the chimes off, you could latch the lever in the raised position until it clears the cam, then use a solenoid, servo, etc, to release the lever at the precise time for the chimes. Would be better if you could shift the cam to be slightly ahead of the clock, then trigger the chimes off the position of the gear for the minutes hand.

If you are getting concerns that the chimes are not striking precisely at the correct time, I have a feeling you will get even more complaints when the chimes are correct by UTC, but half a minute off by the clock itself.

Robin2:
Am I a luddite for thinking it is a shame to introduce electronics into an antique clock?

Mr Harrison was able to make very accurate clocks long before electronics appeared on the scene.

...R

I agree. Attack the source of the issues and use the original type technic. And require help from people having experience of those old beauties.
Don't use Plastic Padding stuff.

I've read up about the NPL 60KHz atomic time signal, but I note comments about it's unreliability and susceptibility to interference.

If you decide to use that I have a receiver that outputs the time code (not decoded) once per second, actually, I have several. You are welcome to one FoC. I have code that runs on a PIC18F2X4XF22 which you are welcome to have but you will have to figure it out and adapt it to your purpose. It creates a clock synchronised to NPL and uses a 32768Hz crystal to keep time when the NPL signal isn't available. There's probably Arduino code ready written that will do the same job, or you could write your own.

Fantastic project BTW! :slight_smile:

Tom,

I've slept on this, I offer to build the electronics for this, probably around the NPL / MSF clock receiver and of course FoC. If you are interested let me know.

Perry