I have had several requests for directions on how to build an inexpensive master clock. I built this type of clock back when I first began collecting Standard Electric slaves, and used it to power my clocks for about eight months before obtaining my current AR-2A master clock.
I received ideas from the alt.horology usenet group and an electrician friend that helped me come up with this design. If you have any questions, please feel free to contact me at email@example.com and I'll try to help you through any rough spots!
The principle of this clock is quite simple - you are simply switching a power supply for about two seconds once a minute. This activates and then releases the magnet in your slave clocks, making them advance one minute.
1. You will need a regular battery quartz movement. Discard the minute and hour hands, as you'll only be using the second hand. Cut the second hand down so that it's about one inch in length.
2. On the end of the cut second hand, super glue an "earth magnet". This is a very small sliver of a magnet, and can be obtained at Radio Shack. (In fact, Radio Shack is going to be your friend for this entire project).
3. I mounted my quartz movement in one of those black plastic "project boxes", also available at Radio Shack.
4. While you're there, browse through the burglar/fire alarm section. You'll find a door magnet for the Radio Shack alarm system. There are two types - the rectangular shaped, and the round shaped. The round one is significantly smaller than the rectangular one. You want the round one. It's about 1/2 the size of a dime with two wires coming out of it. I believe it can withstand a current load of 50mA. Make sure that it is a N.O. (or normally open) switch. While, you're there, you may want to also pick up a 1.5VDC 50mA power supply AND the power supply appropriate for your clocks. Series clocks use 200mA power supplies, parallel clocks use 24VDC power supplies. You shouldn't wire series and parallel clocks in the same circuit. For my series clocks, I use one of those step up transformers that start at 1.5, then 3, then 6, then 9, then 12 VDC, all at 200mA. You may have to increase your voltage as you add more series clocks to the circuit. My AR (AR-3) and AR-2 clocks all run on one transformer, at 24VDC 1000mA. I initially used a transformer at 24VDC 500mA, but it didn't provide enough current to reach my more remote clocks (my system spans three buildings, the furthest clock being about 300 feet away from the master clock).
5. You'll also need a 1.5VDC relay. You should be able to find one of these at Radio Shack as well. If not, you'll have to go to another electronics store. The relay is what's going to actually switch the power supply that is feeding your clock circuits. I used a 4-pole relay - meaning it can switch four power supplies at once. I used only two of the poles - my series circuit (200mA) and my parallel circuit (24VDC).
6. O.k., now that you have the door alarm magnet, mount it so that the earth magnet on the end of your second hand will sweep very close, but NOT touch the magnet. The earth magnet will close the circuit in the door alarm magnet during it's sweep, and release it as the sweep passes.
7. Using the 1.5VDC power supply, wire one side (black) directly to the relay, wire the other side (white), through the door magnet wiring to the relay. I also purchased a momentary push switch at Radio Shack, which I wired across the door magnet as well. This allowed me to manually advance the clocks by pushing the switch (each push advanced one minute). Now, when either switch is closed (the push button or the door magnet), this will provide the power to activate the relay.
8. Now, wire your clock power supply (the 200mA for series or the 24VDC for AR clocks) to the relay. I do it the same way as the magnet switch - I wire the black side directly to the clock wiring and the white side to through the relay. Now, when the relay is activated, it will provide the power to the clocks. When the relay is disengaged, it cuts power to the clocks, making the magnet release and the hands advance.
9. Your series clock will essentially have ONE wire going to them in a big loop. Your parallel clocks will have two wires going to them in pairs. See diagram.
Hopefully this will give you enough of a "head start" to get your own primitive master clock going. I've seen elaborate takes on this design, with flashing lights and bells and whatnot.
Return to SETCLOCKS - A tribute to The Standard Electric Time Company