PLL constant speed motor control?

[Guest Alun]

I've just thought of a possibly new way to regulate the speed of an electric motor!

On the end of the motor shaft you connector a normal optical speed sensor that will output a frequency that varies on the motor speed this goes to one to of the inputs of the phase comparator the other goes to an external oscillator, the output goes to a motor speed controller.

The speed sensor could be a circular piece of plastic with shaded areas at regular intervals with infra-red LED and photo transistor at either side.

Any oscillator whose frequency is the same as the output frequency of the speed sensor you want to use should do. You could use a crystal oscillator trough a divider or frequency synthesizer, or just a bog-standard 555.

The speed controller is a standard PWM or PPM speed controller, this must be voltage controlled like a VCO but varying the duty cycle instead of frequency. Sorry Ante you're lamp dimmer circuit is no good, here unless you want to add loads of op-amps ;)

A 556 could be put to good use, one part could be the speed controller, the other as the oscillator.

I don't know why I thought of this I just did, I have no use for this what so ever!!!

So I haven't bothered to do draw a schematic, it's just a block diagram at the moment.

If this is of any use to anyone I might draw one.

Please let me know what you think.

Has anyone seen anything like this before or have I invented something brand new?

[ante]

Hi Alun,

Sorry but what

[Guest Alun]

Has this been thought of before?

Does anyone have any schematics?

I've heard of a PLL being used to control AC motors but never DC motors.