Circuit for driving bipolar stepper

I've made circuit for driving unipolar stepper (see http://ideal.lv/tmp/unipolar_driver.png). This will not work out with bipolar steppers, because there is no common wire to attach power supply... Can anybody help me to figure out similar circuit for driving 4 wires bipolar stepper motor?
The motor I want to run comes from sparkfun (see http://www.sparkfun.com/commerce/product_info.php?products_id=9238)

One way to do it is to use an H-bridge like the second schematic on this page:

http://www.tigoe.net/pcomp/code/category/code/arduinowiring/51

Wow, thanks for quick reply.
So how do I know what h-bridge do I need for running this stepper?

look at amp ratings
sparkfun motors are not so big so L293D will probably do quite nicely
solder 2 on top of each other to get more amp through
But only if the motors are to big.

David

EDIT: L293D handles 1A so it will do the stepper takes 0.33A
The Driver should have 1x L293D for each stepper you use.
Add heatsink, drivers get hot when used heavily.

I've wired up circuit with l293dONE motor driver chip. Motor drives just fine, but the problem is - chip gets very hot when operating at 12V - is this normal?

Well "very hot" is open for interpretation.

H bridges generally get warm to hot when running, you should probably put a heatsink on it if it is "very hot", or even a heatsink and a small fan.

"very hot" is like I could put my finger on it for about 10 secounds, but not any longer... :slight_smile:

Add heatsink, drivers get hot when used heavily.

Stepping motors get hottest when they are not turning, not when they are heavy loaded.

is like I could put my finger on it for about 10 secounds

That's just on the limit of being OK.

Is it a FET or bipolar H-bridge, bipolars run hotter.

Do your motors need 12V for the rated current? If not you might be over cooking them.

Stepping motors get hottest when they are not turning, not when they are heavy loaded.

That is my definition of HEAVY use, breaking or holding the coil at at a max power.

piggyback the H-chip if you feel it is running too hot (or/and add a fan), the current will be shared between two chips then.

@grumpy_mike, he is using sparkfun stepper, they're rated 12V 0.33A

David

[edit]Is there something to limit the amperage to 0.33A on the circuit?[/edit]

L293D handles 1A so it will do

Yeah, and people "handle" working 24-hour shifts. The problem is that, if you do that routinely (or worse, continuously), they die.

The 1A is a "won't immediately catch fire if you hit it momentarily" rating. Even the 330mA motor is pushing the limits, if you're running it continuously at full power (i.e., not PWMing the enable pins to reduce the average current). That's why the chip is getting uncomfortably warm.

Well Yess, but most driver boards that I have seen have "something" pot to limit the current flowing to (though) the chip and motor so the stepper can be run faster with more volts or just to make sure that the motor/chip does not fry.

So is the motor drawing more ampers than the 0.3A it should get?
it is probably taking the full current from the powersupply through the direct wired chip.

David