Telescope drive motors that don't...

[Dodgy Geezer]

Well, I tried!

In fact I don't have to double up the delay - it's 130x125, so I just alter the values.

Making the delay shorter (5x5) results in no movement from the motor at all - but I expected that would be too fast...

Making the delay longer (250x250) results in slower movement, but with the same low torque. It's just as if the L293D is only sending one pulse to the coil, rather than holding the coil on until the next change occurs. Surely if you:

MOVLW HSTEP1 ;(hstep1 is FF, for example)
MOVWF PORTB

this should leave all PORTB pins high until PORTB is changed? Or perhaps the L293D only sends one pulse to the motor, and I need to increase the current or duration on this in some way?

[falingtrea]

Silly question. Do you have the VS pin (pin 10) of the L293D parts connected directly to the battery? Or is it connected to the 5V supply? That pin supplies the voltage that actually drives the motors and should not be going through the regulator.

[Dodgy Geezer]

No, very sensible question!

The circuit I have assembled is precisely as advertised here: http://telescope.marford.me.uk/Proje...controller.htm .

You will see that I am using a 16 pin L293D, where VS is pin 8, and this is what is connected directly to the battery positive. So there should be lots of power available to the L293D.

I think it is unlikely to be a failed L293D either, since the circuit actually contains two PICs driving two seperate L293Ds (with slightly different programming), and both of them display the same problem. This circuit is advertised as a working stepper motor driver, but I am coming to the conclusion that maybe it is not!

[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.