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Topic: L297 stepper motor controller (Read 21 times) previous topic - next topic


Jan 31, 2006, 02:33 pm Last Edit: Jan 31, 2006, 02:34 pm by Daniel Reason: 1

I think Massimo is in Sweden and I am in Canada, near the pacific, so here is part two of your international answer!

In terms of the 12V motor supply and the clean 5v supply, the answer lies with the motor. When a stepper motor turns on, it draws large amounts of current into its windings. A small motor could draw 10 amps for a few milliseconds, for example. These large current draws make the supply voltage drop, unless your power supply can handle it.

Supply voltage drops are bad news for microprocessors! This is why the two supplies are always best spearated: never run any inductive load from the same supply as the microprocessor. You are asking for unpredictable trouble if you do.

Another reason for separating the supplies is to prevent noise from getting back into the microprocessor. Motors and inductors put out a large voltage spike when their fields collapse, and you don't want this to get back into the microprocessor supply, so you use a separate supply.

The general rules are:
- try not to drive anything with an arduino pin that draws more than a few milliamps- say 10ma or so.
- try not to drive large loads that source their current from the arduino's regulator, as this might interfere with the stability of the Atmega8's power supplies.
-never drive an inductive load that sources it's current from the processor power supply! Use a separate supply.

Hope this helps!


PS: the larger the filter cap on the motor side of the regulator, the better: there really isn't a limit, but in practice anything up to 470uF on the 12V side would be reasonable. You can add as much as you want.

Massimo Banzi


Massimo is in milan , the capital of design :)

I subscribe to everything you wrote in the post.

I guess the stuff we wrote here could be turned into a nice article for the website.


Flat Stanley

Well, I've certainly been finding both of your advice very helpful! so i would second that motion!

I'm planning to breadboard the circuit very soon, so I will post some pictures of that, and the final schematic that I use. After this, I intend to make a circuit using the l297 and the ULN2075B to control a unipolar stepper.

Also I have a nice working circuit that uses a TTL 74194 shift counter as the transalator. I'll post some picures of that too (under a different topic). I'm interested to compile a group of circuits to control both unipolar and bipolar steppers, that offer a range of price vs functionality options.

Just for the record...

Jonathan is in London, the capital of rain and tea!

(and i changed my user name to 'flat stanley' for those who remember my 'little accident' just after the London workshop!)
my hobby --  www.jonathanbryan.com

my life --  www.ifranks.com  [link]www.silver-collector.com[/link] [link]www.da

Flat Stanley

I just checked the farnell site for the l298 and it is listed as no longer stocked?????

Any idea why that might be?? I'm worried that these chips are on their way to retirement!!

Is there some other setup which I should be investigating??

any advice would be nice!

my hobby --  www.jonathanbryan.com

my life --  www.ifranks.com  [link]www.silver-collector.com[/link] [link]www.da



any advice would be nice!


It's probably not stocked anymore since Europe is going RoHS compliant, and it's not compliant.

Try this: usually a nice email to the local sales rep will get you three or four samples. Offer to credit them in your next show. Failing that, I believe the chip is still widely available in North America: try this!

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