Quartz clock motor reversible

The standard quartz clock motor seems to be some sort of stepper but with only one coil. The rotor has a single north south permanent magnet in it and the coil is briefly pulsed with polarity reversed on alternate pulses. So in that sense it is a bit like driving one coil of a bipolar stepper and I am using half an L293D to drive it. It was easy to cut the circuit tracks and solder some leads on which exit the case through small drilled holes.

The direction is apparently controlled by the shape of the pole pieces (maybe a bit like a shaded pole motor). However I have found that the following set up can give stable running in both directions. By stable I mean if you try and reverse the second hand it just stops and then continues in the required direction. Torque seems about the same in both directions.

Applying a pulse of 6ms and then waiting 500 ms before applying the next (reversed) pulse results in anti clockwise motion. Increasing the pulse to 25ms results in clockwise movement. The wait time can be reduced to 100ms and still give reliable operation.

This may be useful for those wanting a meter type display as the quartz kitchen clock is cheap and often the paper dial is reversible allowing another scale to be easily added.

Is a direct drive from an 08M possible ? maybe a pair of 2.5V zener diodes in series across the 4.5V supply with one end of the coil going to the mid point. The other end of the coil would go to an 08M pin. With the pin as an input no current would flow but with it high or low current would flow through the coil. Could this work and is some protection against inductance needed ?

Indeed a handy hack,with clocks no doubt available cheaply via coin shops! I presume (being the clock's second hand) that there are 60 steps of 6° per rotation? With just one coil a simple bipolar driver may be possible, or even direct PICAXE drive. What sort of current does the clock motor take? A suitable reversed diode should handle any induced emf problems.

FWIW I'm continually on the look out for reliable bulk supplies of low current motors for assorted projects, both stand-alone & PICAXE driven, & these could fit the bill nicely. Past orders of suitably efficient "solar" DC & stepper motors from the likes of US outlets Electronic Goldmine/Pager Motors etc have been ideal, but just when a design is standardised their supply often ceases! I've used 100s of EG's ~1V 8mA DC motors to great effect, but they are now no longer available. Most small off the shelf motors from Jaycar etc are much too power hungry, high reving & costly for educational work... Stan

EXTRA: Your breadboard layout is very lucid, but a circuit diagram appreciated please.

Yes it steps in 6 degree steps per pulse applied. Of course a finer resolution is available by using the minute or hour hand !! Maximum speed is about 3 seconds per rev.

The coil resistance is 260 ohms according to my cheap multimeter. I havent tried running with a low voltage but the clock normally operates off a single AA cell. Apart from the motor and display the timing mechanism might also be a useful RTC

Such a high coil resistance means 1.5v/260 Ohms = peanuts (~5mA). Even powered off a 4.5 V PICAXE supply you'd still only have ~15mA, & thus be well inside the 25mA pin source limit. Consider direct drive hence!

I've hacked these clocks for parts before, but have just lashed out NZ$2.50 (= ~£1) during lunch break,& bought another from the local coin shop. Such items as the gear box, buzzer, 32.768 kHz crystal etc alone are worth this! The local Jaycar charges more that the clock price just for the crystal.

Disassembly is easy enough, BUT the movement box innards predictably are a tad too fiddly for the typically impatient "all fingers & thumbs" kids I try to inspire with mad scientist schools work. At such low prices most kids wouldn't see the rationale in bothering of course, & even most patient adults would glaze over- especially if long sighted! Perhaps there's scope for suitably pulsed (PICAXE supplied) external driving- just remove unwanted clock hands!? Stan.

I've been using them to time the accuracy of the picaxe timing functions. The ones I have are epoxy blob internal IC's. Mine won't run on 4.5 volts and not reliably on 3 volts with fresh batteries the second hand just twitches. To get around it, I put a LED on the output pin of the axe to the clock with a 40 uf cap across the led. The LED flashes each second when the clock pulls power at 4.5. With 3 v a pair of fwd biased diodes drops voltage to the clock.

Using DC resistance to try and predict current drain is not going to work. The inductance of the coil is too high and won't saturate with only a ms pulse width.

Thanks for the hack. Well done.

Stan,
I agree that these are pretty fiddly inside and both mine required disassembly to get at the coil connections and therefore not ideal for youngsters. So time machines and rapidly spinning back to the future style clocks are not possible.

On the other hand could a tidal clock be made without disassembly ? They seem to work in NZ http://www.trintec.com/marine/time-tide-clocks.shtml Recognising that Americas Cup fever has probably cooled over the last decade, and that NZ tides are not specially high, there might still be some interest.

All that is needed is to increase the time for the hour hand to make a circuit from 12 hours to 12 hours 25mins and 15 seconds.

If the voltage to one of these clocks is reduced eventually a point is reached where the second hand does not step but just quivers. So the IC is keeping time but the hands are not moving.

Maybe the Picaxe could power the clock at 1.5V counting pulses and then every 30 pulses or so reduce the voltage for a second to lose a pulse. In this way the clock could be slowed to match the tides.

By the way Goldmine is selling the steppers again at a sale price of $1

I have modded clock units for faster continuous rotation to make robots before, torque isn't great but it does work and some can be drive quite quickly - but not necessary in both direction.

We have some good results with some analogue watch modules that we got (can't recall where) & they were very cheap ).70p each I recall but we bought 10 and when we asked for more sold out. These could be made to run very quickly but had a different mechanism with a sort of multi segment rotor inside a can a bit like a strip of the flexy magnetic rubber you can get to stick on fridges.

http://www.ycbclocks.co.uk/index1.html

59p each if you buy 100 - about as cheap as it gets. Good company we used them at school wide range of clock products

http://www.cousinsuk.com/catalog/8/1171/1405.aspx

ultra small unit - ideal for small robots - not the same as we used

http://www.mutr.co.uk/product_info.php?cPath=3_101&products_id=777&osCsid=ada79c5d62598bc0a68c9d742371756c

£1.60 each 0.91 for 100

And of course there is your local pound $ or what ever shop where there is even a bargain to be had for the alert "pull it to bits and re-purpose it type".