Voltage controlled DC motor driver

[slow_rider]

I removed a small DC motor from a tape deck would like to use it to drive another tape unit. The motor has a small dynamo installed on it's shaft and it generates voltage as the motor runs. Since I need to control the motor as accurately as possible I thought to build a simple circuit that uses the voltage generated by the dynamo to control the speed of the motor (=feedback). Does anyone happen to have a circuit like this? The motor runs at 1V - 3V range and the dynamo generates 0.3V when the motor runs on 1.5V for example. I don't have much more info on the motor and no marking on it either.

 

[microtexan]

DC Motor

I removed a small DC motor from a tape deck would like to use it to drive another tape unit. The motor has a small dynamo installed on it's shaft and it generates voltage as the motor runs. Since I need to control the motor as accurately as possible I thought to build a simple circuit that uses the voltage generated by the dynamo to control the speed of the motor (=feedback). Does anyone happen to have a circuit like this? The motor runs at 1V - 3V range and the dynamo generates 0.3V when the motor runs on 1.5V for example. I don't have much more info on the motor and no marking on it either.

Aren't you going to need to know what voltage (exactly) at which the motor runs? Then you can measure the dynamo voltage and then use an error amplifier to adjust the motor voltage.

 

[slow_rider]

Yes, I'll do that. I was asking mainly because I only know to construct a basic err amp with an OA and a voltage devider and the dynamo output is AC and I think that rectifing it might hurt the linearily of the amp. I think I may have used the word dynamo incorrectly and the proper name for the generator is an alternator (whoops).