PWM signal, mixed with a supply voltage?

This project consists of building a microchip that will output a PWM signal, that is consantly being updated VIA given input parameters.

The chip is already completed, it has the ability to controla servo motor 60 degrees in both directions flawlessly. The problem is that I was using a servo for the prototype and it works. However, the motor that it now needs to be used on, is some sort of brushed DC motor.

I know for a fact that the brushed DC motor does what I need to do, because it is off of a car and has already worked, but it only had two inputs so it puzzled me. I did a little reading and and apparently it operates with the supply voltage and the PWM signal together?

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Ok so, what I have, a PWM signal and a supply voltage. The car manufacturer states that it uses some sort of H-Bridge to mesh the PWM signal with the supply voltage. I guess what I'm getting at is how can I build something similar to this, and what will the output look like to the motor.

If i'm unclear in anyway feel free to tell me I didnt explain it well.

The motor i'm using for the final prototype has the ability to be controled to a 45 degree rotation and hold its position with just two I/O pins. I just need to know how this is being accomplished.




Thanks a lot; you guys are always helpful.

A servo consists basically of a motor, a gearbox (to slow it down), an h-bridge (to drive the motor), a feedback device (usually a potentiometer), and the controlling electronics (which compare the feedback to the required position, and outputs a correction signal).

By the sound of things you might have the motor/gearbox and nothing else. What did the motor do on the car?, and what car is it from?.

Nigel Goodwin said:

A servo consists basically of a motor, a gearbox (to slow it down), an h-bridge (to drive the motor), a feedback device (usually a potentiometer), and the controlling electronics (which compare the feedback to the required position, and outputs a correction signal).

By the sound of things you might have the motor/gearbox and nothing else. What did the motor do on the car?, and what car is it from?.

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Well, I know for a fact that the motor is not just a gearbox/motor, otherwise it would either just be on or off and not hold its position.

What i'm thinking is the ECU of the car sends a PWM with a supply voltage together, then splits the signal with its internal circuitry. It's kind of complicated since I dont know exactly what i'm dealing with.

You might look into that “something 10”? system that controls household appliances by sending a signal through the AC house wiring. A capacitor in series will block a DC voltage but pass an AC signal. (easy filter) This is really not my department. The analog guys should know about this.

Yeah, well I found out that its a brushed DC motor. I'm just not sure how to control the angle of it. Someone said use an H-bridge but not sure how exactly that would work.

A H-Bridge (A series of diodes) are used to negate back EMF produced by the windings from your motor. Like the ones shown here

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By the sounds of things, you have a simple DC motor. The amount of circuitry to filter the noise generated by a motor to produce a clean PWM would be crazy. Especially "internally" - closest point to the noise of the EMF etc..

To control your DC motor, use limit switches that tell the motor's driver (an IC/external circuit) to stop, and power the other way, or use something like the L298 shown above. Read the datasheet on the chip, but basically it can control motors in the following manner;

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