Telescope drive motors that don't...

[falingtrea]

Another silly suggestion. Try turning BOD off. Maybe your regulator isn't rock solid enough and BOD is resetting the PIC. The PIC will run at lower voltages than the BOD is set for. Upper level for BOD is 4.4V. According to the code, portB should be static and not pulsed. If this fixes your problem, maybe you could look for a LVDO regulator only a 400mV drop like a STMicro LD29150.

[Dodgy Geezer]

Umm...What's BOD? Are you talking about the regulator? Are you suggesting that I just feed the +5v regulated line from the battery directly, at 6.3V?

The difference seems to be minimal, and I suspect it will cause no damage, but is that what you mean?

Incidentally, I have been looking for any possible difference between what I am doing and the published circuit. The only thing I can see is that the regulator is flanked with a couple of 100nf bead capacitors, and I am using 100nf polyester. Interestingly, the data sheet for the 7805 regulator suggests 30mf capacitors, but I am following the published design. Perhaps there is a problem there...?

[mister_e]

100nF directly at the output + 1 as close as possible of the pic is recommended. 30uF or higher would be nice at it's input. i usually use 10uF tantalum at the output as well as close to the PIC.

Any current demanding device have their own 47uF (or higher depending) + 0.1 uF as close as possible.

BOD: Brown-out detect. It's one of those configuration fuses setting for the PIC you're using.

[Dodgy Geezer]

Thanks for the education!

BOD off is still the same. It might have given a little more torque, or that might just have been wishful thinking on my part.

I have few capacitors on the board, just the ones specified. By now, I'm pretty sure that the PIC is doing the right thing, and that the problem lies with the motor driving L293D circuitry. So I went looking for other drive circuits, and found another which was just like the one I had built!

So everything seems to be right. The problem is, it isn't. Does anyone think it would be safe to up the voltage beyong 6v? The battery pack that came originally with the motors is 6v, and the coil windings are around 18ohm, suggesting 0.3 Amp.

[Archangel]

Hello Dodgy Geezer,
I have a little trouble with assembly, Have you put a voltmeter on the enable pins to see if the pic is pulling them high? As I understand it they should be held high while the stepper is running.<br>
Or Roman Black's Lini Stepper works well I have tried it. Kits for sale on ebay:http://cgi.ebay.com/Lini-stepper-con...QQcmdZViewItem

[mister_e]

Is there any exact motor Model we can refer to?

i found this PDF for those interested in Stepper Motor Basics
http://www.solarbotics.net/library/p...f/motorbas.pdf

Turning the problem in many ways... i'm still thinking of unsufficient current AND/OR voltage at the driver output. I would suggest you to use a higher voltage source, and connect the driver before the voltage regulator. If you have any variable voltage power supply that would be nice. This bring mvs_sarma's suggestion to the front. Make sense, there's probably some voltage loss at the output.

Why the previous driver circuit worked... well hard to tell, no schematic or pic of it (with some part# of the transistor/Mosfet)? Any coils or else fancy stuff on it?

[Archangel]

Turning the problem in many ways... i'm still thinking of unsufficient current AND/OR voltage at the driver output. . . .

Hi Steve, that was where I was going by asking if the enable pins were held high, as I do not understand the assembler . . . I think those ports should not be pulsed . . .JS

[Dodgy Geezer]

Mister-e '..Is there any exact motor Model we can refer to?..'

There are no markings on the motors. The original controller used a 6v battery pack, and the coil resistance is 18ohm. A similar looking motor is the BPM42 from Astrosyn, but that is specified as 12v.

Joe S. - thanks for joining the party! i would be happy to rewrite the code in Basic if that would help, but I think the code is working. I programmed the PIC on a Vellerman 8048 unit, which has a limited test function (6 leds and 4 switches), and the test showed the leds all lighting up at the right times. I have also run the code on a couple of software simulators, and it does what it says it does - holds the specified pins high.

What I cannot simulate is what the L293D is doing (no oscilloscope ). In other circuits I see the possibility of varying the current passed to the stepper, but I don't think you can on the L293D. How does the chip know how much current to pass the stepper?

The Lini Stepper is very interesting, and I would buy one like a shot - if it supported Bipolar steppers like I have on the telescope. Unfortunately, the telescope hardware is fixed. I was wondering about getting one of these - http://www.jafmotion.co.uk/motordrives.htm