Roman,

I wanted to thank you for some excellent code I found on your Website at
www.romanblack.com/one_sec.htm.  It certainly takes all the hard work out of
doing accurate timing on the PIC.

I have just spend all night getting my Tmr0 interrupt working properly - a
few gotcha's with saving the context and resetting PCLATH got it working
finally !  It took me a while to realise that if I am using more than one
code page on the PIC, and my ISR sits in the first code page, the call to
the ISR on Tmr0 overflow does NOT set PCLATH to the code page of the ISR -
so if you do not set it yourself at the start of the ISR after saving the
context, and you have call's or goto's in your ISR - your in trouble !

I thought it might be an idea to post this to the list - firstly your Web
server and mail address seem not to be responding this morning ?  And
secondly - esp. for the newbies on the list - if you are looking for an easy
way to do ZERO-ERROR timing from a few milliseconds to a few seconds, then
visit the above address, and have a look at Roman's method of doing it, and
your sorted !

Again thanks
Ian

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Roman Black
Sent: Tuesday, 11 February 2003 6:10 pm
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: Stepper drive methods....


Wagner Lipnharski wrote:
>
> Roman Black wrote:
> > Sorry Wagner, that's wrong, at low speeds and stopped
> > the motor runs at min heat. At higher speeds the motor
> > inductance means that MORE average voltage is applied
> > per second for constant current, and the motor heat
> > *increases* at speed.

> Not on my motors.  I needed to increase belt reduction to speed up motors,
> so they cool down.
> At +-7 rpm the 5V @ 1.4A they almost boil water, the metalic frame where
> motors are bolted gets hot.  Changing this to +-30 rpm they run smoothly
> warm.  It was not caused by any ring or signal bouce. Power logger simply
> shows the current limit is reached after motor stops after each step, DC
> current, so power average goes to sky.
>
> Note that I don't use constant current, I use 12V and current limit.


Ok, i'll buy that. The one case where the motor runs
cooler at high speed is with a *constant voltage* driver,
BUT generally nobody does this as the resulting very
low coil current gives very low torque at high speeds
making it only suitable for very low power loads.

I'd also suggest that instead of changing your gearing
to cause less motor current and less heating, you could
probably just have lowered the PSU voltage to give
less current and I2R losses and caused the same effect;
less motor heat and less motor torque.
-Roman

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