# Circuit or Method for controlling RPMs of DC Motor

Hi...  I'm looking for a way to control (vary) the speed of a small toy DC motor.

I started off trying the simple method of just adding a 5K potentiometer to

the circuit but that does not provide much adjustment.  I'm using 3 or 4.5 volts

and just looking for a simple circuit that will allow me to regulate the speed from

0 up to full throttle.

thank you in advance for any suggestions or directions to follow.

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PWM (Pulse Width Modulation) is the technique you are looking for. There are many examples of how to control a small DC motor with PWM, which method you use will depend on a few key points:

• Do you need to control the speed precisely? (To match 2 or more motors together for example).
• Do you need to rotate in both directions or forward only?
• What will be controlling the motor speed? A microcontroller? A person with a dial? Remote control?

Hi ...

thanks for the help.

I've been reading a bit on the interweb and yes... I keep coming up with PWM... although i'm not

knowledgeable about that...but will read up on it.  There's nothing fancy about what I'm looking to do....

i've got a small eccentric weight mounted on the output shaft of a small DC motor and just need to

vary the speed..  using either 3 or 4.5 volts.... to get a variety of vibrating effects.

Have a look at this link for a good example circuit:

http://www.pcbheaven.com/circuitpages/PWM_Fan_controller_using_a_555/

for fun I searched for 555 pwm circuit. This is what I got. http://tinyurl.com/alwefya Trust me it is safe. I just didn't want to post the whole google url here. The first few circuits I saw there will only drive the motor in one direction, so, if you were to need forward, and, reverse, you would likely want a motor driver. Even then, adding a motor driver to one of the posted 555 circuits would be fairly simple. Instead of feeding the 555 output to a transistor, you would feed it to the Enable pin and then add a NOT gate, and a switch to allow for forward, and, reverse.

I found a circuit I've been trying to get to work, but no success yet.

I've attached an image showing 3 areas I need a bit of help with.

Are the diodes I have placed correctly, orientated correctly?

Not sure if I have the pot set up correctly... I've got one wire from the #3 pin on the

555 timer going to the middle contact on the pot and the 2 diodes, one going to the left and

one to the right leg on the pot, is this correct?

and really not sure how to hook up the transistor... need a bit of help with that, where the 3 legs get connected to.

Thank you for the assistance and suggestions.

http://i248.photobucket.com/albums/gg198/bocode/pwm-motor-controller_zps6c0c56cc.jpg

Thanks all for the suggestions.  I found a You Tube video which helped me stumble through.  After a few (well, more than a few) builds of the circuit, finally got the thing to work.  Fried a half dozen 555 timer chips... but learned a lot in the process.  I'll post the link to the fellows video.  Someone else may find it useful.  Thanks again.... oddbot, I'll read over the literature you posted. thanks.