Hello all, I have a project involving stepper motors and I need help developing the control circuitry. What I need is a control system that will permit me to run the stepper motor continuously forward as long as I step down and hold a floor pedal. I would like to have an ability to change the speed with a variable pot if possible.

Next, I would like the motor to do an automatic reverse when I step off the floor pedal. I would like to have an ability to change the reverse speed with a variable pot if possible and to also be able to adjust the amount of time the motor is in reverse before stopping fully. The amout of time in reverse could be anywhere from 1 ms to 10 sec. If possible, would like to use pushwheel switches to control the reversing time.

Can anyone offer any suggestions or insites?

Thanks in advance
rmoreno

 

What's a pic microcontroller?

 

Well, maybe we should start a little closer to the beginning.

Do you already have a stepper motor? If so, what are it's specifications?

 

No. Have not identified a stepper motor yet. Will need a motor that has an RPM level of 15 revolutions per minute.

 

OK. 15 RPM is pretty slow; that won't be a problem.

Do you know how much torque you will need?

Do you have a budget in mind?

 

low to medium torque. As for a budget, I'm thinking somewhere around $100 - $250. Is that enough?

 

That should probably be enough.

You may want to experiment first with some really inexpensive stepper motors. That way you won't be too discouraged if you burn up a few of them.

Jameco has these:
http://www.jameco.com/webapp/wcs/st...toreId=10001&catalogId=10001&productId=171601
for $2.95 each; probably as inexpensive as you will find.

They also have Darlington driver IC's, which come in handy for small stepper motor projects like this:
http://www.jameco.com/webapp/wcs/st...storeId=10001&catalogId=10001&productId=34315

555 timers will be a necessity:
http://www.jameco.com/webapp/wcs/st...storeId=10001&catalogId=10001&productId=27422

They're useful for a very wide variety of things. They're so cheap you might as well get a dozen of them or so.

You should start by reading through the datasheets so you can get an idea of what you're getting into.

You will also need a power supply that is capable of putting out various voltages at an ampere or two. Do you have a power supply already?

 

Wow. lots to look at. Yes I have 2 power variable power supplies. Alberto (Senior Member) posted something about a PIC microcontroller. Are those difficult to work with?

 

PICs are great.
There is a steep learning curve associated with learning how to program them.

I don't know how proficient you are in electronic hardware or software.

Stepper motor drivers can be built using just a few logic IC's and a driver, or fewer if you use PICs - you'll still need a driver though.

The nice part about the logic ICs is that they won't require any programming. The not-so-nice part is that if you change your mind about how you want things to work in the future, you will have to make physical modifications to the wiring of the circuit, rather than making changes to the software.

PICs are pretty cheap; some are under $1, many are in the $2-$3 range.

You'll need a programmer. You can get a programmer for $35-$50 right from Microchip.

 

By the way, thanks for all your input. I'm really appreciative for your help.

I've done a few projects already and I think I'm ready to step it up a bit. I think I like the PIC approach for the simple reason that if I want to change the design later I can probably do it quicker and easier with code vs hardware. Do you have any schematics for stepper controls using PICs?

 

Microchip has Application Notes on their website:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2819

Scroll down near the bottom.
Get:
AN907 - Stepping Motors Fundamentals
AN906 - Stepper Motor Control Using the PIC16F684
AN898 - Determining MOSFET Driver Needs for Motor Drive Applications

Here's a very simple introduction to stepper motors:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=2125&param=en542238

 

If you want to use power MOSFETs, you will need to use logic level power MOSFETs if you want to drive them directly from a PIC.

Some of that will be explained in AN898.

 

Thanks. I'm going to download all that I can from the microchip.com website. This looks like this is going to take some time to read and understand. I'm probably going to have more questions after I go this material. Hope you'll be up to answer more questions later

 

If you want to look at a decent programmer/PIC package, take a look at the PICkit 2 Debug Express, about $50.
It includes software on a CD, an in-circuit programmer (the PICkit 2), interconnecting cables, and protoboards, one with a PIC16F887 installed. The PIC16F887 is an 8-bit MPU with 44 pins, has a built-in clock, plenty of I/O pins and onboard ADC.

 

Thanks, I'll take a look at what you have posted. There may be questions afterwards.