Friday, January 08, 2010

Citizen Transistor Clock

One of the readers of this blog emailed me with this clock. I find it very interesting. Firstly, a big thank you to Haja for sharing this with me.

The clock is a Citizen transistor wall clock from the 70s. It has the following functions; hours, minutes, seconds, day and date. It measures 315 mm in diameter. The front crystal is glass and there is a hard board that covers the back.

The interesting aspect of the clock is the movement. It is not a quartz movement but a electromechanical movement. From the picture of the movement, we can see that the movement is powered by a battery. There is a electronic circuit board with transistors, capacitors and resistors. Let me first set the base that my knowledge of electronic and anything electrical is limited to Ohms Law (V=IxR) and that I think anything that is electrical in nature works on PFM (Pure Fxxxing Magic).

OK, lets see if this makes sense. The resistor, capacitor and zener diode provides a smooth supply (from the battery) to the circuit. Another resistor will provide bias for the transistor. The windings on the disk will detect magnets on an oscillating pendulum as it moves. This movement generates a small electrical current or pulse. This will cause the the transistor to turn on and allow the pulse to flow through the second disk. This in turn generates a magnetic pulse that nudges the magnet to keep it going. In simple terms, it is like when you give a little push to a swing when it passes you. This little push keeps the swing moving. Phew. I stand corrected on this.

I was told that the clock is accurate to 5 seconds a day. Also the second hand sweeps like a mechanical clock and does not tick like quartz movement.

As you can see from the photographs, there is a lot of love for the clock. The battery compartment is broken. The owner has use quick tie to hold the battery in place.

There are 2 adjustment crowns on the clock. The crown at the 6 o'clock adjusts the time and day. Turn the crown clockwise to adjust the time and day. I am guessing there is no quick adjustment for the day. The date is adjusted by the 5 o'clock crown. Each pull of the crown moves the date by one count.

Photographs: Haja

All in all a pretty cool clock.