Need Help!- Will this simple controller board work?

[nate89]

Hey guys, this is my first post but I've been doing a lot of reading, especially on this thread:

http://www.cnczone.com/forums/showthread.php?t=37671

The thing is, I don't know how/have the ability to program a pic. I also don't have a lot of money to spend since I'm in college. I was doing some searching and found this circuit:

http://www.circuitstoday.com/stepper-motor-controller



I was planning on replacing the transistors with Tip122's. It appears as though I don't have to program anything, which is great, but I was wanting to hear your guys' opinion on it. I am planning on driving nema 17's then possibly upgrading to nema 23 unipolar steppers. I don't want to buy parts I don't need for a controller that wont work. Please help.

If anyone can suggest a different simple stepper controller that doesn't require programming or cost an arm and a leg that would be great! My knowledge of electronics is limited to cars and a EE course I took last year (I'm a mech/aero engineering student). I can solder the crap out of a board though lol. Thanks guys!

[James Newton]

Well, it may work, but it isn't going to work /well/ It will full step only, which reduces the resolution of movement and can cause your motors to vibrate and miss steps at certain speeds. It also doesn't regulate the current flowing through the coil, so it isn't going to be as fast as it could be given a higher than motor rated voltage on the power supply and a regulating driver.

You can buy a pre-programmed PIC for the Linistepper driver for $6
http://www.ecomorder.com/techref/ecomprice.asp?p=416060
which will give you microstepping, current regulation, and a high power half step mode which is really nice.
http://www.piclist.com/techref/io/st...step/index.htm

The linistepper design is open source, so you can make your own from the schematic or buy a pre-made PCB and stuff it from your junk box or scavenged parts. There are some board layouts available if you want to make a PCB yourself.
http://www.piclist.com/techref/io/st...istep/mods.htm

If you are going to buy the parts, you can't beat the kit price of $30 each (quantity 3)
http://www.ecomorder.com/techref/eco...p?p=416015&q=3 it will cost more to buy the parts at a distributor than to just buy the full kit.

Of course, that schematic you have will cost less in parts, and you can probably build it on a whiteboard. If you don't fry your TIP122's you can re-use them in a Linistepper when you aren't happy with the performance from this one. Don't connect or disconnect the motor with the power on!

Good luck anyway and let us know how it comes out?

[nate89]

Thanks for the info

Here's another one I found:

http://hobbymechatronics.com/project...g-motor-driver


It has the ability to step in 1, 1/2, 1/8, and 1/16th steps. It can support up to 35v and 2.5 amps. The only thing I'm not sure of is if the motor power is connected to the board or straight to the power source? If it is, then is VCC the same as the motor (12v in my case)?

Also, it seems as though the controller is only for bipolar motors (correct me if I'm wrong), yet in the pic, it's hooked up to a 6 wire nema 23. Can anyone clarify this for me?

[doorknob]

Originally Posted by nate89 Also, it seems as though the controller is only for bipolar motors (correct me if I'm wrong), yet in the pic, it's hooked up to a 6 wire nema 23. Can anyone clarify this for me?

You can drive a 6-wire stepper as if it were a 4-wire stepper (with a bipolar driver) by selecting half or full windings (and ignoring two of the motor leads, that is, leaving them unconnected or connecting them to terminals that go nowhere).

[doorknob]

Originally Posted by nate89 The only thing I'm not sure of is if the motor power is connected to the board or straight to the power source? If it is, then is VCC the same as the motor (12v in my case)?

It appears to me that Vcc needs to be different from the motor power. According to the datasheet, Vcc has an absolute maximum rating of 7.0 volts (it is probably supposed to be 5.0 volts nominal).

The motor power comes in to the board via the 6-pin terminal strip that also connects to the stepper windings. The motor power is applied to the driver chip pins labeled VBB1 and VBB2, whereas Vcc goes to the logic voltage supply pin of the driver chip. It's a little more clear in the Allegro datasheet "functional block diagram" on page 3 of http://www.allegromicro.com/en/Produ.../3979/3979.pdf

[James Newton]

The A3979 is $8.31 or so says
http://www.findchips.com/avail?part=A3979
and it drives 2.5 amps at up to 35v

TIP122's cost 0.50 so $2.00 for 4
http://www.findchips.com/avail?part=tip122
and drive 5 amps at up to 100 volts (with really good heatsinks like a CPU fan)
The TIP122's with the first circuit or the Linistepper chip or any other step/direction to wave form converter will cost less and do more and...

...when you blow one, it costs $2 to replace all 4. When you blow the Allegro, you are out another $8.

Having said that, lots of people make drivers with chips like that:
http://pminmo.com/ss3977/ss3977.htm

[nate89]

Would it be better to go with a microstepping board that is more expensive/complicated, or a simpler/cheaper board without microstepping. The resolution of my machine isn't a big consern since I will have a resolution of 4000steps/in (or 0.00025 in/step) which should be plenty. But if micro stepping will make the motors less likely to skip steps, I could take a chance on the A3979 controller (but I like cheap and simple, plus I have all the parts for the Tip controller minus the ic's). I'm really at a loss when it comes to these controllers, it the only thing holding me back lol. I guess what I'm asking is if microstepping is really that important that I should spend the extra money on the more complex controller?

Thank for all the help BTW

[James Newton]

Start simple, grow.

[RMS]

Is it really all that hard to program a "PIC"? I am in the same boat as nate89 and I been looking at diy pic programming boards they look really simple then you run some software. I have never done this myself but I am thinking about it. Maybe someone can help us on that?

As far as purchasing a driver board or kit I was looking at probotix.com as well as the Linestepper V2; or trying my hand at PIC programming myself.