General > General Technical Chat
Cheapo clock tear up.
DrG:
I used to use an old style, “analog” wall clock. It was definitely inexpensive and did not keep time particularly well. Purchased some ~20 years ago, it eventually found its way into storage (and yes, I did remove the battery first). It worked, more or less, and had served its purpose.
For some reason, I decided that I wanted to once again use that old style clock face. So, I took it out and inserted a fresh battery and…nothing.
Investigating further, I quickly found the culprit – oxidation on the (-) terminal. Scraping that off, resolved the problem and I could see the pulsing gear movement.
That first gear, nearest the coil, has a magnet inside. I removed it from its place and inverted it in the picture.
So, the circuitry under the blob, amplifies the crystal oscillation pulses to drive the coil – right? Nice little neat design.
These are more interesting electronically than I had realized, but then again, I am easily amused sometimes.
I still will reinstate an old style face clock, but not this one. Instead I ordered another https://www.amazon.com/Crosse-Technology-WT-3102S-Silver-Atomic/dp/B000AMCAUG with radio setting. I have a wrist-watch with such a receiver that does, in fact, work well enough to never have to set. I am hoping that this one will be as good.
BrokenYugo:
Pretty close, the crystal runs at ~32768Hz (215), which conveniently divides down to 1 pulse per second with simple divide by two logic, that is then amplified to drive the stepper motor.
DrG:
No, I don't think you got that right at all. Not about the crystal, about a stepper motor. That gear is not attached to the shaft of a motor. There is no stepper motor or motor at all. Movement is accomplished by two magnets. One is a permanent magnet inside the base of that first gear. The other is an electromagnet (i.e., that coil). Energizing the coil creates a repelling magnetic pulse that moves the gear - perhaps my non-EE terms leave something to be desired.
So, beyond the crystal oscillator, it would seem that electromagnet pulse width needs to be fairly precisely specified so that only a single gear-tooth move is produced - that is what I think is so neat.
EDIT: Also, I really don't want this to be an argument thread or, just as bad, an "I know more than you thread so I am going to correct you". I think I have the operation of this right. If you KNOW you have it right than feel free to explain and all will benefit. But, please, appreciate that I went through the trouble of taking and posting pictures of something that I though was interesting and entertaining.
Ian.M:
Its a single coil stepper. The magnet aligns with the coil's core poles. Reverse the coil drive and the magnet will turn to align its next pole, overshooting slightly due to inertia. Somewhere in the mechanism there will be some sort of ratchet or friction clutch device that prevents it running back to bring the magnet in exact alignment with the core poles, so that the direction is predictable.
If the mechanism is otherwise in decent condition, that would be a good candidate to convert to a Vetinari clock.
The higher supply voltage will overcome any slight stickiness in the mechanism and you can compensate for the crystal's measured frequency error in the code.
GNU Pterry
DrG:
--- Quote from: Ian.M on January 04, 2022, 07:42:30 pm ---Its a single coil stepper. The magnet aligns with the coil's core poles. Reverse the coil drive and the magnet will turn to align its next pole, overshooting slightly due to inertia. Somewhere in the mechanism there will be some sort of ratchet or friction clutch device that prevents it running back to bring the magnet in exact alignment with the core poles, so that the direction is predictable.
If the mechanism is otherwise in decent condition, that would be a good candidate to convert to a Vetinari clock. The higher supply voltage will overcome any slight stickiness in the mechanism and you can compensate for the crystal's measured frequency error in the code.
GNU Pterry
--- End quote ---
Ohhh ok, I gottya, what you are saying is "Movement is accomplished by two magnets. One is a permanent magnet inside the base of that first gear. The other is an electromagnet (i.e., that coil). Energizing the coil creates a repelling magnetic pulse that moves the gear"- thanks so much for the official explanation :)
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