Need a very simple variable speed stepper drive circuit (HELP PLEASE)

[bigmark1972]

I have an application where I will need to rotate a stepper at variable speeds from 0 to 60 rpm. I would like to have the maximum torque possible (not sure of driving configurarion desired?).
I would like to have this controlled with a simple Potentiometer. I am quite sure this can be done easily and cheaply with standard parts but at this point I am still somewhat ignorant on this issue. I am looking for input from some of you sharp people. I need to keep costs low as this is for a product I would hope less than 15$. I plan to bring to market in the future. Assume I already have regulated dc voltage I just need help with the driver circuit.
Thanks,
Mark

 

[OperaHouse]

How much have you looked? A little search and you can find hundreds. A PIC and 4 transistors will do it. If you have something that takes a lot of drive, look into LMD18245 and forget about that regulated supply. A friend if mine is using a couple of boards from

http://www.embeddedtronics.com

for his home made CNC. They even give you schematic, board layout, and even software. Your request is technically incomplete for a better answer.

 

[bigmark1972]

I have spent a few hours looking into it, like I said I am ignorant on the subject so that makes it more difficult.
I could use a uni or biplor stepper and the load will be very small. What information would you like to have for a complete description? I am open to any voltage of stepper I would like to run in half step mode or full step (whatever mode makes more torque?).

Sorry I do realize the question is somewhat incomplete forgive my ignorance this is not my area of expertise, that's why I am posting this here for all of you EE's and such.

 

[bigmark1972]

Sorry forgot to add, I need this to be completely stand alone, no software or anything. I need no positional accuracy whatsoever simply speed control.
Before you ask I do not want to use a simple dc motor due to the low torque at low voltage, a stepper would be great in this aspect. I need to keep this light and as small as possible.

 

[automatic2]

light load could be handled by a plastic gear set that conviently increases your torque. Load will dictate your drive element. PWM can be had with surface mount devices.

 

[bigmark1972]

I need this system to run on very low power, below 1 amp @12-24vdc if possible. I am generating power with another stepper via a small air turbine. This is really not a typical application so typical solutions arent really useful. I have size, weight, power, cost, precision and reliabilty to consider.
I realize I could simply gear a conventional motor down and
vary the voltage. I like the simplicity of direct drive. The service life of a stepper vs a brushed dc motor is also a plus.
I need to do some more studying, I see how it could be done with a pic but I was hoping for a still simpler solution.

I did find that I can run a stepper with ac using a 90° phase shift between the voltages applied to the motor's two windings with a non polarity capacitor. Perhaps this will lead me to more options as well as not requiring me to rectifty the ac output of the stepper to dc.

 

[itsmoked]

Sounds like you need to do your homework.. That is, lay hands on a few components, a scope, maybe a PIC STAMP to run things in an easy fast way, Hunt up some PIC STAMP application notes that show how to run steppers. Fill in a whole bunch of the holes in your knowledge. Then from the knowledge gleaned you can focus in on your specific needs with confidence.

 

[bigmark1972]

I think I have it figured out.

Using a non polarity capaciter and a stepping motor with 1.8deg step value.
Four steps equal 1 ac cycle.

So, this would give me an RPM of 72RPM
7.2deg per cycle * 60hz= 432deg/sec or 1.2 RPS or 72RPM
Using a solid state interval timer >20 bucks I can achieve what I am trying to do with 2% accuracy. I have found many steppers that meet the specs I require.

 

[bigmark1972]

I did my homework, thanks for the help