Uni-Stepper & simple drive electronics

[chronon1]

I have this picture of a unipolar stepper - I don't know what the connections are -- but I do know I can make it turn by putting negative power to the both black cable leads and putting a positive pulse on each of the colored wires in sequence...

Colors 4 colors and 2 blacks. the motor has 2 'halves' the top is red ylw blk
btm is brn org blk

The next pic is my driver prototyping :
( kind of have it stuffed into a littel closeable cardboard box for dust prevention and to keep room 'tidy')

top board is just 555 clock generation
btm board in a 7474N , 7486N, 7404N and a ULN 2001A -

The invertor is to invert the pulses going into the ULN since this takes inverted inputs - this circuit is from vary basic driving schematics -
I think the .5 Amp , 12V output is enough to make the small stepper spin but
maybe I'm wrong. There is no reference voltage that I'm aware of .

The little motor wwill have a holding torque and if I spin it by hand seems to move in one dir or the other one or 2 clocks but then maintains its 'holding torque' stationary ... this is pretty simple stuff that anybody with a bit of trial and error experience on this probably can solve off the bat .....

thanks for your help .!!!
Eric

[chronon1]

please email at ershe@earthlink.net or 407 474 0822 .....

just trying to get this stupid little unipolar stepper to turn with the simple driving circuit ... maybe the 1/2amp 12v ( 6 watts per step, 4 steps per cycle) is not enough power from the ULN 2001 ?

maybe this 2.3" motor needs more current well it says 12 V and 36 ohm coil ..
and good ole' ohm's law says e = i*r or i = e/r which is to say i = 12/36

One may possibly conclude that the current needed is 1/3 or .33 amps, but if that's the case then my .5 amps should be more than enough - driving the whole thing with a 100 watt old pc power supply. I would say that all the chips and the motor don't need 100 watts to run - but what could be the problem is the Voltage drops when current gets drawn and small signals don't have the proper levels - the circuit looks so simple ... why doesn't it work -- damn - if i could just find that serial cable for my RS probescope and look at the signals >>> ( thats' the problem with moving in a hurry.. stuff gets lost all over the place..){

[pminmo]

The 2001 should drive the motor. Are you sure you have the phasing correct to the motor? Looking at your components, you are probably running a similar circuit to the one on my website here, but we used cmos and discrete fets:

http://pminmo.com/discrete/discrete.htm
there are 4 links, including the copper pattern layout to do a single sided PCB via toner transfer.

Phil

[chronon1]

Hey Phil -- nice site ! nicely done ---

Yeah - it shouldn't matter wether or not your driving logic is TTL or CMOS -
just that the interface between the 2 has to be administered properly.

ANy way , the same logic control .. a clock , a binary counter, J-K flip flop ( to temp. store ), a quad nor gate ? -- well i dont have my ckt i n front of me but i will try and post the link next time -

but i don't even know how my stepper works ,,, according to everyone the stepper needs its own power and mine just has 2 black leads and the 4 colored leads --- so i dont know how that works except the power comes from the pulse which also turns it .

perhaps my phasing is off .. ... --- but i have the outputs driving LED's so i can watch the sequence ---

i'll just recheck the wiring ...

here is the ckt link


neil.frasier.name/hardware/stepper/ttl.html

[chronon1]

sorry -- i should have done this the 1st time .. of course your gonna make a typo when there are more than 20 characters and 4 forward slashes and 3 dots !

http://neil.fraser.name/hardware/stepper/ttl.html

[pminmo]

The uln2001 is an open collector sink driver. You can't hook it up like the schematic you linked too, which is wired as a source driver. i.e. source when on ties the coil to 12vdc, sink ties coil to ground. You can use a 2001, but not emulating the schematic shown.

Phil

[chronon1]

and that is why i'm at the board to find people that know this stuff better than me ...

what i attempted in this case was to invert the input to the 2001 so that it might output opposite --- but , when u say open collector, i tend to think i'm not going to get some logic reverse nice and pretty because now we're dealing more with an amplifier and not a logic gate -- the signal level just went from low current to very high and now we are talking big amplifiers to get the .5amps out --- ..

so i need to ... reverse the 'sink ' somehow or find something to improvise .. or just replace the 2001 with 4 generic xsistors for the + output ?

thanks,
eric

[chronon1]

Perhaps the 2003 can be used in place of the 2001 : from

http://www.doc.ic.ac.uk/~ih/doc/step...2/connect.html :



The ULN2003 / MC1413 is a 7-bit 50V 500mA TTL-input NPN darlington driver. This is more than adequate to control a four phase unipolar stepper motor such as the KP4M4-001.



It is recommended to connect a 12v zener diode between the power supply and VDD (Pin 9) on the chip, to absorb reverse (or "back") EMF from the magnetic field collapsing when motor coils are switched off

[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
You can't see the nice illustartions here but on the site page they have something that i think i need to implement into my circuit and motor connections -- they have the motor black wires going to the +12 ? and pin 9 of the 2003 connected to power via zener.

[pminmo]

2001 and 2003 are basically the same configuration. If you take the 2003 pin 1,2,3,4 and hook them to you 7486 outputs. Take the corresponing 2003 outputs 16,15,14,13 to the coils on your stepper. Wire the center taps of the motor to +12vdc. Pin 8 of the 2003 to gnd, pin 9 to plus 12. You should be able to operate the stepper, if you have the coil phasing correct.

Phil

[chronon1]

The Allegro ULN2001A-ULN2004A are a seven Darlington arrays devices.
In fact, the only difference I see between the 01 and 03 is that the 01 is designated as a general purpose, DTL, TTL, PMOS and CMOS --
--- Where as the 03 is referred to interface with only the 5V TTL, and CMOS logic families.
I would think I should be able to use the 01 in place of the 03 since I am driving with TTL from the 7486N. Is this what you believe as well ?

[chronon1]

GOOD NEWS --- well after the bad -- i havent hooked that boxed circuit up in at least a week maybe 2 or 3 -- it is late and i smealt something .. always a bad sign -- .. had connected power backwards to the logic and the 7486 chip was very hot so it needed replacement .. then i isolated just the timer .. and accidentally hooked it backwards but pulled power in time .. anyway -- the damn thing works !

i had that little motor spinning backward and forward, slow and fast ( seemingly several RPM's .... before it stalled and i had to turn my little pot. back down)...
oh what a joy .. i have been trying to get that damn thing to spin by electronic control, on and off )time allotments towards project)( since last ... getting near a year !!! There is not enough torque to resist the heavy pinch of my thumb and index finger but i think i can turn a 1/4 -20 screw enough to raise a tiny engraver / mini-router ---- good thing i started on the Z -axis for it even though i couldn't get the motor control working .... i knew someday i would , TODAY WAS THE DAY !!!

Why the heck would the mfg make the 2 common wires black that need to be hooked to POS ? this goes against all standards and norms....
the other problem was i didn't have pin 9 of the 2001 going to POS.
those were the 2 problems.
i should mention i have a 7404 inverter in this ckt taking the output of 7486 into the 2001 - perhaps i dont need it .. ill try that tomorrow .. this is very exciting ...
i am happy .. joyed.. elated .. eureka vaccuum ... (it's kinda late)...

i'm still pissed off at the mfg. for labeling common as something one might hook to the negative power !!!!
Thanks for your help Phil - I even took a short video clip of motor turning slowly, and fast and backwards and forward ... .. hope to upload that sometime for people to laugh at ? ha ha .. ( 'little things mean alot' !)... and thanks for the hosts of this terrific web site for haveing the possibilities in this forum....

[pminmo]

great news!

Phil