# Clock driver

Discussion in 'General Electronics Chat' started by andrewd, Feb 23, 2013.

1. ### andrewd Thread Starter New Member

Feb 23, 2013
3
0
I need a clock driver of 1 pulse per minute. Clock mechanism is a pair of coils that require a positive 24Volt pulse for one step followed by a negative 24V pulse for the next step. This polarity alternates each minute. There is no second hand. The 'armature' is magnetic and is geared to a 2" diameter brass gear. Can anyone help with a circuit or source please.

2. ### Brownout Well-Known Member

Jan 10, 2012
2,375
998
Tell us what the current requirement for the pulse is, what is the pulse duration? What is the accuracy requirement? Will the driver need back EMF protection?

3. ### timescope Member

Dec 14, 2011
298
44
Hi,
Some more details are needed:
What is the required pulse width
What current is required to drive the coils
Is one side of the coil grounded
What supply voltage is available.

It can be done with a crystal controlled oscillator, a frequency divider and a driver circuit for the coil.

Timescope

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
I was thinking something along the lines of a Real Time Clock, but that typically needs a uC.

In addition to the above questions:
What circuit is the part of? e.g. adding on to an existing circuit, or building one from scratch do do only this specific task?

5. ### andrewd Thread Starter New Member

Feb 23, 2013
3
0
Thanks all for your responses. First 'call' was to see if I got a hit!
I have sorted out the generator. The innards of a cheap battery clock gives me a good crystal oscillator, I have taken a 1 second pulse across the coil and it is driving a LED through an old PNP transistor. That actually is giving me 2 second pulses (at about 250-400mS) due to polarity driving the transistor. The coil has opposite polarity for each second as the magnetic arrangement is similar to the old clock mechanism.
I need a divide by 60 or 30 and suitable driver for polarity changing, or 2 separate divider circuits as the electronic clock has opposing polarities on the coil.
The old clock has 2 coils parallel connected in opposition to drive the mechanism. The clock has 24V stencilled on it but drives reliably on 18V @ 24mA. 24V @ 31mA. It does need back EMF suppression.
I thought of driving it with 2 x 9V batteries as they should last a fair while.
Clock needs less than 1 second pulse duration to be reliable so say 1 sec pulse.
Cheers!

6. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,435
1,305
You can do it with two 4017 decade counters. Wire one as /10 and the other as /6 so cascaded they give an output event for every 60 pulses.

You might need a simple 555 etc on the output to make a proper (and adjustable) length for the output pulse.