Need help purchasing circuit components

[Xyius]

Hello all,

These questions might seem very silly but it is my first time purchasing electrical components and I want to make sure I buy the correct ones based on my OWN LOGIC. I do not just want to blindly follow directions to build this motor controller without knowing the logic behind the parts that I need.

A few weeks back I made a post about constructing a circuit to control the speed and direction of a DC motor. The link to what I have in mind is below.

http://www.electronics-project-design.com/DCMotorDriver.html

Now, I know they have the components listed to buy, but my question is, how would I go about figuring out what to buy myself? What I mean by that is, if I was making this circuit from scratch without the aid of the website, how would I know what types of components to buy? I ask this because I want to have some insight into the design aspect of the circuit instead of just buying the parts blindly. My guess would be this..

-Find a potentiometer From that potentiometer determine the voltage ranges that will go into the Op-Amp.

-Find an OpAmp and determine what is the maximum voltage the Op-Amp will put out based on the voltage ranges found.

-Get two Transistors that have a base current requirement of the current coming from the Op-Amp.

-Get an electric motor that will run on the current from the transistors.

Does anyone have any good sites to purchases electronic components? Does Radio shack sell them? I found a site called http://www.mouser.com it seems to be very good but I tried looked up potentiometers and they only had "digital potentiometers." I do not know about digital ones, the ones I had in mind were mechanical, meaning you turn a knob and it changes the resistance.

 

[Valerie Park]

Thanks for your help!</code>Yes, Radio Shack does sell electronic components. They have a wide selection of resistors, capacitors, transistors, and other components that you may need.For the potentiometer, you may want to look into linear or logarithmic types. Linear potentiometers have a linear resistance curve and are good for controlling speed applications. Logarithmic potentiometers have a nonlinear resistance curve and can be used for controlling volume levels in audio applications.When selecting an op-amp, make sure you choose one that is compatible with the voltage range of the potentiometer you've chosen. You should also consider the slew rate, input impedance, and output power of the op-amp when making your selection.For the transistors, you'll need to select ones that can handle the current coming from the op-amp. You also need to make sure the transistors are matched in gain and leakage current, as these factors can affect the performance of the circuit.Finally, you'll need to select an electric motor that can run on the current supplied by the transistors. The voltage and current requirements of the motor will determine the type of power supply that you'll need.Mouser is a great place to purchase electronic components, and they have a wide selection of potentiometers. They also have a search feature that can help you find the right components for your project.