A Quick and Easy Way of Running ex-GPO/PO
For those of you who aspire to own a working ex GPO/PO
slave clock but do not have the money to afford or have the space for a master
clock (e.g. type 36) and all its associated wiring and relays etc, here is a
"quick and easy" method of achieving this.
method was devised for those with limited knowledge of electronics and/or
construction of printed circuit boards, and as such the accuracy of the timing
functions cannot be guaranteed, but it is a good, cheap starting point.
whole thing is based upon a Velleman kit "adjustable interval timer"
MK3 Available at Maplin for the very reasonable cost of £4.99 (Maplin cat no.
VT27E). This kit which comes complete with all components and a pre etched PCB
and is all you need apart from the battery and some wire.
kit requires basic soldering skills to complete and comes with graphic
how to complete it ,when completed the kit can provide a pulsed output (via a
relay) adjustable between 2.5 seconds and a minute, so set it for 30 seconds and
hey presto 30 second pulses to operate a slave clock (the length of the pulse
can also be set from 0.5 to 5 seconds).
The kit runs off 12v and if you use this
same 12v to operate the coil in the clock the whole thing can be run from the
same battery , there is no need to worry about limiting the current through
contacts because there are none and the relay in the kit can handle 3A at 24V so
the 12V battery will do it no harm, the output will easily operate two or three
clocks in parallel as well.
easiest way to supply the 12V is with 8 AA size batteries (8 x 1.5V) in a
battery holder (Maplin cat no. RK44X @ 69p) and a PP3 battery clip (Maplin cat
no. HF28F @ 29p) no switch is needed, to turn it off simply disconnect the
battery. This way both the circuit board and the battery easily put behind the
clock, and can be secured with double sided tape or even Blu-Tak or similar.
wiring is simple, after connecting the battery clip to the terminals marked
+12V/-12V take a second wire from the +12V terminal to the clock, link the -12V
the NO (normally open) terminal and another wire from the COM (common) terminal
to the clock (the polarity at the clock is not important) and that's that.
practice and with careful adjustment of the variable resistor (part of the kit)
I had mine running at ±2 seconds i.e. pulses every 28 to 32 seconds, this sounds
bad, but the early 28 second pulses tend to get cancelled out by the late 32
second ones. And I did say quick and easy, not 100% accurate, but at around a fiver
its certainly worth thinking about.
those of you with a master clock already running or a number of slaves around
the house etc, a unit adjusted to run at fast pulse rate (I got mine down to
under 1 second) makes a wonderful way to adjust your clocks fast as putting a
clock forward by an hour only takes 60 seconds, much better than standing
holding the advance key.