Motor control example vi query

[Greg Flynn 01]

Hi

I was looking at the example vi, which can be found at the link below

https://decibel.ni.com/content/docs/DOC-16983

It is very similar to a project I am building. In the example, the author is using PID to vary a voltage between 0-5 volts, and then sending this voltage to the base of a transistor.

The transistor then allow battery voltage to flow to the motor. I don't get this. I assume the motor is Volt as he is using a 9 volt battery? To vary the speed of the motor, should he not need to use the PID signal to alter the duty cycle of a PWM signal which would be then used to switch the base of the transistor at a varying frequency to control the speed of the motor?

Why is he sending a varying voltage to the base of the transistor? The transistor is just being used as a switch, yeah??

The system above obviously works, but I don't understand how it works

Any advice???

BTW, I am using a 12 volt motor which is drawing a 4 amps nominal

I can reduce my 12 volt battery voltage using a voltage divider if necessary

Many thanks

Greg

[Greg Flynn 01]

Did some research this morning on transistors. I now understand a varying voltage at the base...he is using the transistor as an amplifier.

He is using a 9V battery. Is this because the motor is 9V or because the mydaq analog output is 10V.

I have a 12V motor. Will I need to reduce my batt voltage to 9V?

[Lewis_G]

Hi Greg,

He is using a 9V battery because the motor is 9V.  If you have a 12V motor, you will need a 12V battery.

The analogue output from the myDAQ is connected to the Base of the transistor.  The base is the gate controller device for the larger electrical supply (your myDAQ).  The collector is the larger electrical supply (the battery), and the emitter is the outlet for that supply (connected to your motor).

More info on how transistors work here.

Hope this helps.

[Greg Flynn 01]

Thanks Lewis

I understand it now

Regards

Greg