BDC's are voltage-sensitive devices. That's good for us because we understand voltage. If you apply enough voltage across a BDC, it moves. If you apply more voltage, the motor moves faster. Reverse the voltage and...you guessed it, the motor moves in the reverse direction. Remove the power and motor moves freely, aka. "freewheeling." And you can stop the motor quickly like a car "brake" by...let's hold off on that for now.

There are about 3 ways to control a motor:

1. Simple & discrete components
2. Common ICs
3. Microcontrollers & drivers

For the talk I'll likely go over the 3 ways for each type of motor. Let's get to it!

Simple & discrete components

While we all would like to have a cooling fan that runs an RTOS, a simple potentiometer is all one really needs to control the speed of a DC motor. Add a DPDT switch and now you can also change directions. If you're going this route, you'll almost always want a pot with a switch to make it easy to turn off the motor.

Protip: always use a flyback diode. It will prevent your controller from going boom when stored energy in the motor needs a place to go. Also, many App Notes add filter caps as optional but they're a good thing to use if you're in an embedded context where RF noise can mess you up (as opposed to say, an industrial HVAC.)

What if you want stepped speeds like slow and fast? A rotary switch with a resistor at each step makes a nice collection of voltage dividers. Values of each resistor per step will depend on the motor, voltage and desired speed.

Now for the last open question: how do you stop quickly using only simple components? You're not going to like the answer...basically you disconnect the power and replace it with a resistive load so any stored energy dissipates as heat. Don't forget a heatsink on the load if you're working with large motors.

You may wonder why I don't have any schematics. Those will come when I start the actual presentation deck and will be shared here as well.