# Control Project

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#### Sebastian Pozo

##### New Member
Hello,
I have to make a control system that mantains constant speed of a small car prototype using a DC gearmotor regardless of external disturbances such as slopes (small slopes).

For the development of this project I thought that a posible solution could be a control system consisting of a PID controller that affects a PWM generator circuit thus regulating the speed of a DC motor.
I am not able to use a microcontroller so I dont know how can I modify a PWM with the output signal of a PID stage. Which anallog circuit can modify a PWM after a PID controller stage?
The output of my PID contoller it is going to be a signal, how this signal can modify a PWM? Which circuit can I make?
What can I do ?

Thank you!
Regards

Sebastian P.

#### Pommie

##### Well-Known Member
You need to be a way to measure the speed of the motor. How will you do that?

Mike.

#### Sebastian Pozo

##### New Member
You need to be a way to measure the speed of the motor. How will you do that?

Mike.
I will measure the real RPM of the motor by using an optical sensor which is going to give me pulses, and then ill use the lm2917 that will transform pulses to a certain voltage value. And this is how I will do the feedback of the system.
Thanks
Sebastian

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#### Pommie

##### Well-Known Member
If you google "opamp PID controller" you will find a few examples. These will give you a voltage out that is proportional to the voltage needed to keep it at a constant speed. This could be used with a power transistor to directly drive your motor. What is the stall current of your motor?

Mike.

#### Sebastian Pozo

##### New Member
If you google "opamp PID controller" you will find a few examples. These will give you a voltage out that is proportional to the voltage needed to keep it at a constant speed. This could be used with a power transistor to directly drive your motor. What is the stall current of your motor?

Mike.
Operating voltage range: 3 V - 6 V
Current without load (3 V): 150 mA
Current without load (6 V): 200 mA

Shall I use a power amplifier ? just one transistor? (tip 31?)(H bridge?)

Thanks

#### alec_t

##### Well-Known Member
An H-bridge wouldn't be necessary unless the car is required to reverse.

#### Sebastian Pozo

##### New Member
Thank you very much for your help!

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