Sorry it has been a bit quiet but we had a few weeks in France and got distracted catching up on jobs there. A minor update on this will follow.
I brought back a 30 day rope driven clock to work on for a fellow engineer who lives in France. The movement has a 1 second pendulum and is marked as being made by Lawson of Bingley. I haven’t found much wrong with it other than the hands were a loose fit on their arbors and were rubbing against each other and the dial.
In the course of working on the clock I needed a different style pendulum sensing optical sensor to interface to my Mumford Microset Timer. This evolved before being modelled in Fusion 360 and then 3D printed. A small sensor interface PCB module was also created in Fusion Electrical and milled on my Tormach CNC mill. The body integrates the laser emitter, detector and PCB. Below is a visual image from Fusion. The pendulum swings through the U channel to break the optical beam and give pendulum timing pulses.
There are various M6 modelled mounting holes around the body. The complete unit is powered from the Microset internal 5V supply.
A complete write up is available for download on the link below.
Update : – I could not get the clock to accurate time while using a 3600 beat reference in the Microset. I did a train count and discovered that the clock is actually a 3584 beat movement. The clock is now doing very well with a few seconds per day error.
If you are a regular reader of this blog you will know that I have got involved with the local church clock which is a Cooke of York movement. I have been working with a fellow engineer in the village to try to bring the clock to time and we are slowly getting there. Our last major breakthrough was finding the fly was lose on the gravity escapement arbor. Since tightening the fly the clock has been much more reliable.
There is a weight tray on the pendulum which has an assortment of coins in it where someone historically has been fine tuning the pendulum swing. Because the clock has been running fast by a few seconds per day we have been slowly removing the coins one by one to bring it closer to time. I think it is now at a point where we need to monitor it long term with the Microset.
Bryan offers an upgrade to the Microset that allows a temperature sensor to be added to the recorded information. There will almost certainly be temperature changes in the clock tower so it seemed like a good idea to upgrade with the temperature option. This was ordered and duly arrived from Bryan and is now fitted. There is also an upgrade to allow the Microset to record data into internal storage in the Microset rather than depending on having a PC connected. I would be more comfortable leaving just the Microset in the church pendulum cupboard rather than my portable PC so I also ordered this upgrade.
It took me about an hour to do both upgrades on the Microset. The memory upgrade involves a chip change inside the device and the temperature monitor needs an additional 3.5mm jack socket fitting and wiring to accept the new temperature sensor. Neither is a difficult task but clearly need to be done carefully so as not to do any damage to the Microset. Bryan’s instructions are well written and illustrated.
Since the upgrade I have been running the Microset on the bench with a Smith’s clock movement. (It is actually the one I stripped down, cleaned and rebuilt on my ‘Clocks 1’ course at the BHI). The new Microset facilities seem to work well and as expected.
A New Sensor Needed – 1st Attempt
To implement measurements on the church clock the supplied optical sensor as shown in the picture above is not totally ideal. It has a very narrow gap between the transmit light source and the receiver detector diode which on a turret clock is not easy to use.
It is possible to get round this my fitting a cocktail stick or similar to the pendulum bob and using this to break the beam but it is a bit messy. I had picked up a bag of laser diodes and detectors at a local ‘ham’ radio junk sale and I decided these might form the basis of a new sensor which might be more useful to a large pendulum assembly. Bryan is a really helpful guy and although he does offer a larger laser sensor he was more than happy to help me with the required electronic interface to the Microset. The one proviso is that the amount of current drained from the Microset 5V power supply must be kept below 30mA.
I set to and made the most elegant and over engineered solution for my laser sensor. This is shown below. The black mountings were designed in Fusion 360 and 3D printed on the Sindoh 3DWOX.
The spacing between the emitter and detector is adjustable by sliding the transmitter along the steel rods. The power to the laser is also carried down the steel rods. A small DTC transistor provides the interface to the Microset and the 5V supply provided by the Microset is dropped via two diodes to power the laser. It works really well ….. but … when I went round to the church to install it I realised I should have checked one or two things first. The rating nut at the bottom end of the pendulum (used to make course adjustments to the pendulum length) was almost touching the floor of the pendulum cupboard. My wonderfully elegant laser detector would not fit under the pendulum to monitor the swing. A serious re-think was needed. The gap was so narrow that at best I will only be able to get a piece of 16 SWG aluminium sheet or PCB underneath the rating nut.
A New Sensor Needed – 2nd Attempt
I did say I had a bag of laser diodes and detectors so a new version would be possible and I could then save the posh one for more public facing activity.
As mentioned above I decided to use PCB as the base board. This is shown below.
This has the advantage that I can use the copper surface to mill tracking into it to aid the wiring. The downside is that it is quite flexible and therefore possibly not stable enough to keep the laser aligned with the detector diode. To resolve this I soldered strips of nickel silver (could have been more PCB) either side of the centre line as shown but leaving a gap for the pendulum swing.
I designed a common holder for the laser and detector diode in Fusion 360 and 3D printed two of these on the Sindoh 3DWOX.
The finished detector assembly still had a tendency to flex so I stuck some old pieces of credit card on the lower surface, one at each end before the mount and a large piece in the middle. This seemed to cure the problem without adding significantly to the base thickness.
When plugged into the Microset all seemed to work well. Here is a typical PC display of the Microset data.
I now need to get it installed in the church tower.