PIC to ULN2803 to Stepper Motor Interface - Electronic Circuits Projects Diagrams Free

jenny1985 · 1st May 2007, 02:31 AM

Hi,
I connected a PIC16F84 to a ULN2803 5volt driver to a 5volt 6-wire stepper motor. The motor was running for about 20 seconds, then stopped and it will not start again. Even if I turn off power and turn it back on.
Here is my code to control / pulse the stepper motor.
Attached is my schematic. Any idea why it would quit and then not work again?
Jen

start

movlw 0x00
tris PORTA

loop
movlw b'00000101'
movwf PORTA
call DELAY_20
movlw b'00001001'
movwf PORTA
call DELAY_20
movlw b'00001010'
movwf PORTA
call DELAY_20
movlw b'00000110'
movwf PORTA
call DELAY_20
goto loop

Peter_wadley · 1st May 2007, 03:28 AM

The ULN2803 continuous collector current is 500ma - so you most likely didnt burn the transistors out..

The code looks fine, although im do not know which digital sequence is used to drive unipolar stepper.

Although I highly doubt it - could the stepper be out of range of the magnets (though i didnt even think this is possible)

If it made a full rotation then the above problem should not be consider^

I wish I could give some better insight.. im sure a more expierenced member will post soon.

Goodluck

Peter_wadley · 1st May 2007, 03:30 AM

Forgot to mention to try with the other 4 transistors of the ULN array.. if they motor moves like normal immediately turn the power off so you dont kill the transistors..!

Then use power transistors or MOSFETS.

Russlk · 1st May 2007, 03:43 AM

You don't have current limiting resistors at the input to the ULN. The PIC can output 20mA minimum, the max is not specified. Perhaps the base-emitter junction is fried, use your diode checker to see if the ULN input still looks like a diode.

Peter_wadley · 1st May 2007, 05:12 AM

Quote:

You don't have current limiting resistors at the input to the ULN. The PIC can output 20mA minimum, the max is not specified. Perhaps the base-emitter junction is fried, use your diode checker to see if the ULN input still looks like a diode.

the ULN2803A has a 2.7kW input resistor for 5V TTL and CMOS.

House0Fwax · 1st May 2007, 08:10 AM

You don't have the ULN2803 grounded In your schematic.

Have a look at this.
http://www.voti.nl/stepbots/
Stepbots

Hope this helps.

jenny1985 · 1st May 2007, 01:42 PM

Sorry... Actually, yes I do have it grounded. I just neglected to put in the gnds on the schematic to speed things up for posting the picture. Yes, it was very weird, it worked for a while then stopped, I reprogrammed the PIC with some updated code and tried it again and it worked for about 20-30 seconds then stopped and didn't go again.
Any other ideas?
Jen

House0Fwax · 1st May 2007, 04:02 PM

Quote:

Originally Posted by jenny1985

Any other ideas?

Try monitoring the outputs of the pic with LEDs ( with series resistors ) and see what happens.

What are you using to power the circuit ?

justDIY · 1st May 2007, 08:30 PM

try using a simpler step sequence like this:

1000, 0100, 0010, 0001

also make sure your leads are in the correct order

... you may also want to slow down the pace of your steps a little, try increasing the delay between each step.

gramo · 1st May 2007, 10:02 PM

Yeah, if your steps start to fast, its not going anywhere.. been there before

Russlk · 2nd May 2007, 12:33 AM

Is MCLR tied high? A floating pin will cause that problem.

Peter_wadley · 2nd May 2007, 01:09 AM

Quote:

Originally Posted by Russlk

Is MCLR tied high? A floating pin will cause that problem.

That could definately be the problem right there.

jenny1985 · 4th May 2007, 12:45 AM

Got it!
MCLR needed to be tied high via 100 ohm resistor... and I had to lower my delay - it was a little too quick.

Thanks for all the help guys! You have proved to be a valuable resource!

Peter_wadley · 4th May 2007, 03:59 AM

Quote:

Originally Posted by jenny1985

Got it!
MCLR needed to be tied high via 100 ohm resistor... and I had to lower my delay - it was a little too quick.

Thanks for all the help guys! You have proved to be a valuable resource!

Glad to hear!!

gramo · 4th May 2007, 05:30 AM

Quote:

Originally Posted by jenny1985

Got it!
MCLR needed to be tied high via 100 ohm resistor... and I had to lower my delay - it was a little too quick.

Thanks for all the help guys! You have proved to be a valuable resource!

woot, nice work

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1st May 2007, 03:28 AM	(permalink)
Peter_wadley	The ULN2803 continuous collector current is 500ma - so you most likely didnt burn the transistors out.. The code looks fine, although im do not know which digital sequence is used to drive unipolar stepper. Although I highly doubt it - could the stepper be out of range of the magnets (though i didnt even think this is possible) If it made a full rotation then the above problem should not be consider^ I wish I could give some better insight.. im sure a more expierenced member will post soon. Goodluck __________________ "Stick around" - Arnold Schwarzenegger in The Predator after impaling a soldier to a wood post 9vDC Guitar Pedal PSU PIC16F84a Game Module

1st May 2007, 03:30 AM	(permalink)
Peter_wadley	Forgot to mention to try with the other 4 transistors of the ULN array.. if they motor moves like normal immediately turn the power off so you dont kill the transistors..! Then use power transistors or MOSFETS. __________________ "Stick around" - Arnold Schwarzenegger in The Predator after impaling a soldier to a wood post 9vDC Guitar Pedal PSU PIC16F84a Game Module

1st May 2007, 03:43 AM	(permalink)
Russlk	You don't have current limiting resistors at the input to the ULN. The PIC can output 20mA minimum, the max is not specified. Perhaps the base-emitter junction is fried, use your diode checker to see if the ULN input still looks like a diode. __________________ see my website: www.geocities.com/russlk

1st May 2007, 08:10 AM	(permalink)
House0Fwax	You don't have the ULN2803 grounded In your schematic. Have a look at this. http://www.voti.nl/stepbots/ Stepbots Hope this helps.

1st May 2007, 01:42 PM	(permalink)
jenny1985	Sorry... Actually, yes I do have it grounded. I just neglected to put in the gnds on the schematic to speed things up for posting the picture. Yes, it was very weird, it worked for a while then stopped, I reprogrammed the PIC with some updated code and tried it again and it worked for about 20-30 seconds then stopped and didn't go again. Any other ideas? Jen Last edited by jenny1985; 1st May 2007 at 03:22 PM.

1st May 2007, 08:30 PM	(permalink)
justDIY	try using a simpler step sequence like this: 1000, 0100, 0010, 0001 also make sure your leads are in the correct order ... you may also want to slow down the pace of your steps a little, try increasing the delay between each step. __________________ If you don't have a planet, what good are gold bars? want to contact me directly? gmail gordonthree check out my project website: http://projects.dimension-x.net Favorite numbers: 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

1st May 2007, 10:02 PM	(permalink)
gramo	Yeah, if your steps start to fast, its not going anywhere.. been there before __________________ Spency. PIC Micro's - Your mind is the limit PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net

2nd May 2007, 12:33 AM	(permalink)
Russlk	Is MCLR tied high? A floating pin will cause that problem. __________________ see my website: www.geocities.com/russlk

4th May 2007, 12:45 AM	(permalink)
jenny1985	Got it! MCLR needed to be tied high via 100 ohm resistor... and I had to lower my delay - it was a little too quick. Thanks for all the help guys! You have proved to be a valuable resource!