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Simple Control of a DC speed controller


I'm about to purchase 2x 12V motor speed controller to drive a remote control golf trolley (4QD Porter). They can be controlled via 0-5K resistor or 0-3v. I want to use a picaxe 28 to control the speed, what would be the easiest way to control them ?

I would prefer not to have a servo mechanically driving a pot, is there a simple solution.

Please assume total ignorance, i am very new to this.

Many thanks.

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I recommend you put together something like this:


Have you ever used a PICAXE before? I suggest you look up PWM (Pulse Width Modulation) in Wikipedia if you're unfamiliar with the term.
Basically what the above circuit does is take an oscillating digital signal (from the PWM output) and average it out into a relatively smooth analog signal, suitable for sending to your motor controller's input. If the PICAXE is running off a 5V supply then your PWM DIY analog output will be able to produce a signal from ~0V to ~5V, so it'll cover the full input range for the controller.
I've left off the values for the resistor and capacitor (R1, C1) for now, since I can't remember the typical PWM output frequency for a PICAXE 28, but those are easy enough to figure out later.

In addition to the RC circuit, an unity gain op-amp circuit should be added as a buffer, as detailed in this Microchip Appnote 538.

Even better would be a 3/5 gain op-amp; then the maximum 5V PWM output would be scaled down to the 3V maximum input.
Although the op-amp buffer is definitely a sensible addition, it's hard to tell how much benefit you'd get from it since we don't know much about your motors drivers. Do you have a part name you can give us?

Many thanks.

Yes i have used a Picaxe, well i say i have i have just fiinshed the 'My first robot' walkthrough from frits. And apart from a little bit of extra findling with it thats about it.

But that looks like what i'm looking for - i will research PWM and see where it leads me.

Thanks again !

Is this a golf cart? To ride on? If so, we are talking BIG motors and a ton of current here. Be aware of that.

No not a golf cart just a powered trolley (just for the golf bag)..
I cant believe it can be this difficult to find a way to control speed via a microcontroller.. i must be missing something i'm sure!

You said the motor can be controlled by either a variable resistor or a 0-3v level, so it probably has its own driver on the motor. Just use Telefoxes circuit but be aware that a 5v microcontrollers full PWM will be 5v and not 0-3v.