Alternative motor control for NBTV

[kareno]

In the past I had great success controlling motors by sensing their commutator switching. This can be done by detecting small pulses on the motor voltage, which occur six times per revolution for most small DC motors.

The attached scheme would allow this to be exploited for NBTV synchronisation. As there is no absolute indication of motor position using this method, a manual phase control is required and I have chosen to make this behave like the motor case rotate knob on the Baird televisor and other sets. So it's actually in keeping with past practise!

The controller will hopefully lock to provide a still image, following which the rotary encoder is turned to obtain correct frame lock. There may be a requirement for a motor speed control too, but I haven't included that in the diagram and in any case I would achieve that analoguely (is that a word?!) i.e. by use of a potentiometer connected to the FET. The rotary encoder allows the framing to be adjusted to a resolution of approximately 1% of a line.

If I did this I would cram it all on a PIC and hopefully create a board that requires no input other than separated line sync pulses.

[roger63]

Hello,
Why don't you use the G4JNU pll circuit ? It is very efficient and I used it on all my machines, nipkow disc and mirror screw.
look at http://la-radiovision.fr
Roger

[kareno]

I have used Peter Smith's motor controller, Roger, and it works well. But I'm always willing to try something new.

[roger63]

Sounds great. Good luck .
Roger