Motor control - RPM + Power

[Mark_guest]

Good day to all !

I need some light on this problems :

1.) How to calculate the correct RPM ( turns ) of motor ( HW is done )

2.) How to measure the exit "power" ( in volts ). ? This volts ( in range 1-3 V ) are sended to some other device, but before i send them to this end device, i want to display them, and i want to check if the sended volts are OK.

Any suggestion is welcome !

[jma_1]

Greetings,

One method for measuring RPM would be to use an optical encoder and then examine the pulses. Alternatively, if the motor is coupled to a gear assembly with a lever arm, a feedback potentiometer could measure position. Position would not give you RPM, but it would enable inexpensive feedback for closed loop operation. Without more information on your application, and what you intend to do with the motor RPM I cannot suggest anything more.

Back EMF can be tricky to measure. Most pics have A/D measurements, but the circuit must be able to handle both positive and negative values based on the commanded direction of the motor. Try searching the web for more information of back emf measurements and sample circuits.

The data sheets on the parts listed below should give you at least a starting point of things to look at.

possible h bridge drivers: LMD18200, SN754410NE
alternatively: build your own :-)

If you want to determine if the connections to the motor are ok, you can alternately measure current flowing throw the motor (high side or low side measurement).

Cheers,
JMA