Joe,

I don't know yet.  When I get a chance I want to look at some more 
waveforms using a couple of high-wattage resistors to simulate the motor.

Here is a link to a guy using the same driver chips that I am:
http://www.buildyouridea.com/hardware/arcsin/fab_a/oscope_1.jpg  (8th 
microstepping)
Interesting that he has a similar irregularity to mine near the bottom.

I'd be interested in seeing some of your waveforms.

More photos of mine:
Full Step (Both Phases On): 
http://www.bright.net/~agarb/STMC/Both%20Phases%20On%20Full%20Step.jpg
Full Step (One Phase On): 
http://www.bright.net/~agarb/STMC/Wave%20Drive%20Full%20Step.jpg
1/2 Step: http://www.bright.net/~agarb/STMC/Half%20Step.jpg  (really 
ugly, but timebase is faster than other photos)
1/4 Step: http://www.bright.net/~agarb/STMC/4th%20Step.jpg (another fast 
timebase)
1/6 Microstepping: http://www.bright.net/~agarb/STMC/6th%20Step.jpg
1/8 Microstepping: http://www.bright.net/~agarb/STMC/8th%20Step.jpg
1/10 Microstepping: http://www.bright.net/~agarb/STMC/10th%20Step.jpg
1/16 Microstepping: http://www.bright.net/~agarb/STMC/16th%20Step.jpg
The board: http://www.bright.net/~agarb/STMC/Board.jpg  (Not too 
professional, but it's only the second board I've ever done.)
Debugging: http://www.bright.net/~agarb/STMC/Debugging%201.jpg

Sometime I just need to google for a tutorial on making a decent 
website, so I can write everthing up, show thumbnail photos, a link to 
download the firmware, etc.

Aaron Garber

Joe McCauley wrote:

>Aaron, 
>
>Your waveforms look lots better than the ones I've been getting with Appnote
>906. What do you think is causing the irregularities in the waveforms at the
>bottom & half way up? 
>
>I've had to shelve my work on appnote 906, but will be getting back to it.
>
>Joe 
>
>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
>Aaron
>Sent: 07 June 2005 13:13
>To: piclist@mit.edu
>Subject: [EE] Stepper Motor Idle Current Reduction
>
>
>Hi all,
>
>I just got my 18F252-based microstepping bipolar stepper motor driver 
>(for a little hobbiest mill I am retrofitting to CNC) working yesterday 
>afternoon.
>
>The driver uses National Semiconductor's LMD18245T Full Bridge chips. I 
>would like to add idle current reduction, but am not sure of the best 
>way? I was thinking about PWM'ing the DAC reference of the driver chip 
>instead of leaving it tied to +5v. Any thoughts appreciated....
>
>Schematic: http://www.bright.net/~agarb/STMC/schematic.gif
>Screen shot of 16th microstepping mode: 
>http://www.bright.net/~agarb/STMC/16th%20Step.jpg
>
>Aaron Garber
>
>(Sorry, James, I couldn't find what I considered to be a good deal on 
>some appropriate unipolar steppers, or I might have bought some 
>linistepper kits....)
>  
>

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