A Vintage IBM Clock
In its early days, IBM produced many products you might not expect. Among these were industrial wall clocks. I got one from eBay and made it work using some 21st century technology. Here’s the story of the clock. There is another story describing my clock controller if you are interested in reading it. Finally, I added an hourly chime feature (a cuckoo, actually) and I wrote an article about that also.
The Vintage IBM Clock
As a vintage (retired) IBMer I am fascinated by IBM’s early products. Recently I saw an IBM clock on eBay that got my interest. I decided that this 1930s-era relic needed a new home, so I purchased it.
After researching how such clocks work, I knew I would not just be able to plug it in and see it run. Industrial wall clocks like this one were used throughout factories and schools beginning in the 1920s. A given building might have dozens of such clocks, and a requirement was that they all show the same time. That is because in a factory where the shift ended at 5:00, every worker in every room watched their clock and packed up to leave when it said 5:00. It would not do if the guys down the hall left a few minutes early because their clock was a few minutes different than your clock.
IBM’s answer to this problem was a clock system ruled by a master clock that synchronized its time with every remote clock in the building. An invention in 1919 patented by the International Time Recording Company (which became IBM in 1924) described how this master/remote synchronization worked.
As this was 1919, synchronization was done by ingenious electromechanical means. It involved the master clock sending 24 volt DC pulses every minute on one or the other (sometimes both) of two lines to all the remote clocks in the building. The pulses either advanced the remote clocks one minute or caused them to run fast or slow until their time matched the master. Every minute the electromagnet-driven ratchet-and-pawl mechanism in the remote clocks made a clunking sound that I know people eventually got used to hearing.
Note about two lines and not just one. It’s too much to explain here, but two lines, call them A and B, were used in this system to allow the master clock to keep the remote clocks on the same time. If you are really interested, there is a video that explains in detail the synchronization magic. And if you actually understand this, there may be a Nobel Prize in your future!
My fascination with vintage IBM clocks began in my youth, I suppose. I went to elementary, junior, and high school in Vestal, NY which is just across the river from Endicott, NY, the home of IBM. Naturally, IBM got the contract for the clock systems in all of the local schools. The school buildings I attended used IBM clocks that operated on the same master/remote principle that my new-old clock uses. That’s how I know folks got used to the incessant clunking of the clocks every minute. In class, the clunking was actually a welcome sound. Class would end soon.
After my clock arrived, I was immediately concerned I would never get it to work. I knew how to apply a 24 VDC signal to cause the internal mechanism to advance the hands by one minute. I tried that with no result. I tore the clock apart and discovered that the synchronization mechanism that coordinates the two 24 volt signal lines from the master was the problem.
Since I did not purchase a master clock (these are costly), and since I have only one remote clock, I do not need to use the original master/remote technique to run my clock. I do need a master controller of some type to supply a pulse every minute, but I do not need to use the synchronization hardware. So I simply removed the synchronization mechanism that was keeping my clock from working. The remaining mechanical hardware works fine with the synchronization contacts and cam followers disengaged. Now I can pulse the coils directly with 24 vdc pulses every minute to advance the time. Clunk, clunk, clunk…
The Raspberry Pi Clock Controller
To drive my clock, I decided to build a controller based on a Raspberry Pi. I programmed it using Python. The controller uses a button-driven control panel for setting the clock and it delivers one pulse per minute to advance the time.
I am recently finished writing the story of the clock controller. That story delves into my code and may not interest you. But if you are interested, tap here to read it.
Thanks for reading.
