Choosing Stepper Motor - Driver Combination

Question

This is my first attempt at designing/building my own circuit and PCB, so please bear with me. I am building a small, portable device that makes use of a small, accurate motor. My goal is to make the unit as small as possible while still achieving a higher torque capability.

Finding A Stepper Initially, I began laying out the motor features I wanted: high degree of accuracy, efficiency (low power requirement), small size with reasonable torque capability, and 360-degree rotation.

Ultimately, I resorted to the 28BYJ-48 stepper because I was having a difficult time finding something between the slightly more expensive/bulkier NEMA and the microsteppers -- neither of which met both goals of the project. I have a few concerns regarding the quality of these motors, namely, the efficiency and life of the motor.

Figuring Out The Correct Stepper Driver I know that the L293 is a common choice for driving small motors, but clearly I'm a glutton for punishment and decided I'd find a different option! After hours of mindless surfing, I had to remove myself from what became a sand trap. (I will say, I have a much greater respect for the development( invested time) of those little PCBs that carelessly end up in landfills).

Anyways, I digress, I am going to stick with the road already travelled and use the L293DD (surface mount). Is there a better option that someone might recommend, or perhaps a better method of searching for components?

ATTINY10 (1024bytes) to upload a small program I wrote that details the operation of the motor.

Is the driver a good choice for my small project. I know that these motors can be purchased with their own driver board, but I've just started using Eagle and would like to design my own PCB -- outfitting the board with different parts and minimizing the overall size of the housing and the design layout to one PCB. There will not be a lot of load on the motor, so I don't intend the combination to reach any maximum values.

Can anyone recommend a good resource to learn about PCB design?

Answer 1

Sparkfun.com has some good tutorials on PCB design with eagle which is free. (with some restrictions). Upverter.com is also a good place to cut your teeth on, the learning curve will be slightly higher but less part creation which will save you time. As far as PCB design goes, make sure you have adequate power caps next to power hungry IC's. Find a PCB trace width table on the internet and make sure your traces can handle the current going through them. Typically you make big power\ground planes because it lowers the inductance and resistance of the copper on the board. You can think of each trace as a tiny resistor and inductor, you can actually calculate the values of each trace/plane. A big ground plane also gives a place for RF from processors or PWM to go to and makes traces less of an antenna. If your doing a two layer design it makes fitting the power planes into the PCB more complicated because you it forces you to run traces through your ground plane. This is where PCB design turns into more of an art, you are trying to balance multiple requirements. The picture here kind of illustrates this.

Start out by:

1. A ground plane on the bottom layer
2. Place your connectors and IC's, place them where it makes sense and rotate them to avoid crossover of traces
3. Route your power, using appropriate trace sizes
4. Route your digital signals (under 20Mhz, you probably need to worry about where they go too much, over that and it turns into more of a science)
5. You may have to repeat steps 2 through 4 and get better results

Then check the @#$^ out of your board before you send it off, make sure your schematic is sound, check all inputs\outputs and vcc and ground. Do they make sense? did you reverse anything? Did you get all the pins right and correct to the datasheets?

Then check the PCB. Are the pads the correct sizes on the parts? Do you need mounting holes? Do you want test points to make it easier to troubleshoot? (Oh and vias carry current, did you size those right as well?)

Then send it off, if it works 100% after you stuff it you'll be my hero.