Control the speed of a dc motor.

I have a team assignment and need to control the speed on a dc motor.
I've done a little bit of reading about PWM and SCR but actually I don't have a clue of how to desgin this driver.



This is a picture of a board with a microcontroller which we may use.
The Microcontroller is a PIC18F4550 but we only have acces to 10 of it's pins 1 of which is ground two other 3.3V and 5V and 7 i/o pins.

We are restricted in the use of components, here's a pdf but it's in dutch so probably not very useful: Project document (dutch)

We can use other components if we have good arguments for their use but this is not advised.
We are also on a budget of 20 euros if that matters.

The driver wouldn't have to be very sophisticated at all, we need to set a speed wait a couple of minutes and then set another speed for a couple of minutes. This doesn't sound difficult to me but I have no idea of how to implement it in hardware.

Any help is much appreciated.

take a look at some of the arduino shields. This might give you a clue.
You can also flash the pinguino bootloader on the PIC so you can use the arduino software to progam everything.

(if this is still needed)

Thanks for the reply.
I just switched an input/output pin with the necessary duty cycle, I know this is frowned upon given that the micro has PWM built-in but it worked.

Maybe for the next time:

Check the pdf and see witch pins have PWM (I think only 2 or 4 on this type of µCPU)
Normaly you also need an other pin to descide the direction of the motor and you can also use a 3th pin to enable or disable.

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Regards,

Maarten
(Belgium)

We used a normal input/output pin instead of the onboard pwm because whoever made these boards decided not to solder any connection to the pins that are pwm enabled.

(leuven, belgium)

ziet er een leuk bordje uit. Waar heb je het gehaald als ik vragen mag?

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Regards,

Maarten
(Belgium)

Werd voorzien tijdens het vak Probleemoplossen en ontwerpen aan de K.U. Leuven.