The Shop > Electronics & IC Programing
Stepper Motor Control
vtsteam:
Ahhh, okay so we have an additional engineering specification -- battery powered. And the original spec said conventional solenoids were out because of jerky movement. This is getting tough!
I'm going to say you need very low mass for the moving figure, a crystal oscllator, divider, and an output component to drive the motor (jfet?) --- and a very low power low speed brushless motor, maybe something even that you wind yourself. I imagine a slow rotary solenoid or semi-motor with a stop and a spring/elastic return might even be the deal.
I wouldn't use a computer, since the oscillator and divider circuit it would need to have (or have added) are sufficient in themselves to do the job if chosen properly.
catceefer:
"I'm going to say you need very low mass for the moving figure, a crystal oscllator, divider, and an output component to drive the motor (jfet?) "
"I wouldn't use a computer, since the oscillator and divider circuit it would need to have (or have added) are sufficient in themselves to do the job if chosen properly."
This is largely the route down which I am now heading. I contacted the constructor of the clock in the video and he kindly sent me the details of the solenoid control and coding. Essentially, it uses a microprocesser that is programmed via a deleloper board. The processor is built into a circuit that uses a separate crystal chip and the relevant circuitry to supply the power. The coidng includes steps that effectively increase and decrease the power to the solenoid so that it operates and releases more smoothly and sedately. This element of the coding is not used in the clock in the video, though.
I have just ordered a developer board so that I can make a start on learning the relevant coding. I have done programming before, but in VBA and VB4, some years ago, and I have mostly forgotten it all.
Regards,
James.
picclock:
Hi
A thought occurred to me whilst I was reading this interesting thread. It would be possible to take a standard clock/watch movement and take the actuator coil output and use it with a driver circuit to power your solenoid system. It would be relatively easy to cause the driver current to ramp up and down slowly by using a capacitor in an integrating configuration. This would be simple, cheap, and use minimal power.
Might be worth a thought
Best Regards
picclock
catceefer:
Piccloc,
That idea is worth a thought, I agree. I did find a thread somewhere online where someone used an old quartz clock innards to run a different clock. I have now purchased a TI Launchpad to try and programme a microprocessor chip to use in a control curcuit. If I am successful, I shall try and make the chip operate at times other than just one minute to add other features to the clock. If I fail, I shall look into your suggestion further.
Regards,
James.
picclock:
Hi
In order to get reasonable accuracy from a small microcontroller its best to use one which has a timer/counter. This is a register which counts in response to various events, one of which is normally the cpu clock or a divided version of this. When the the timer over/under flows this then sets a flag or changes a status word which can then be cleared by your program and the appropriate action taken, like output a signal. Because the timer/counter continues counting regardless of the code running it maintains the same accuracy as the clock, which if its a 32768 Hz crystal will divide nicely into 1 second chunks.
If you try to make a timer using a timing loop in the code itself it is difficult to maintain accuracy because of the different time taken for the various code branches. Although these can be padded with nop's its unlikely to produce a good result. Also, controllers use more than one clock cycle per instruction so working out how many clocks your loop will take can be a challenging issue. For instance a conditional jump instruction could take 1-3 clock cycles depending on whether the condition was met and how far in memory the jump was.
Good luck with your programming endeavours
Best Regards
picclock
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