Recommendations - Model Train Controller

[Darrel Taylor]

The 12F675 can run 4mhz on the internal clock. You should be able to easy incorporate the TMR0 interrupt and make a software PWM output that'll run at 3.9khz (which should be plenty high enough) and use the A/D input to set the duty cycle on that PWM. ... Are you familiar with doing software PWM based on interrupts?

I'd be interested to know how you could do that.
And since Malcolm was attempting to use MY software PWM routines based on interrupts, I guess you could say I'm familiar with them.

Let's see, 4 channels @ 3.9khz with 8-bit resolution.

That'll take (3900 *256) = 998,400 interrupts per second.
With a PIC running at 4mhz, it'll execute 1,000,000 intructions per second.
That leaves, 1.0016... instructions per interrupt.

You wouldn't have a code example for that would you?
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[skimask]

I'd be interested to know how you could do that.
And since Malcolm was attempting to use MY software PWM routines based on interrupts, I guess you could say I'm familiar with them.

Let's see, 4 channels @ 3.9khz with 8-bit resolution.

That'll take (3900 *256) = 998,400 interrupts per second.
With a PIC running at 4mhz, it'll execute 1,000,000 intructions per second.
That leaves, 1.0016... instructions per interrupt.

You wouldn't have a code example for that would you?
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Well, yes, I've seen your PWM routines, and fine routines they are, as are most of possibly 100% of the items you post...........ppppfffffffttttttt (that's me fizzling out)

AND I had a brain fart! I had a whole paragraph typed out explaining my position when I realized I forgot the final divide by 256 for the software PWM. Yep, 15.25hz is about the top for 4mhz. That is unless you start sacrificing resolution for speed...but it still doesn't get you up into the khz range, which is what I did to get a 4khz PWM signal in the blower motor project...then again, I only needed slow, fast and a few speeds in between for that one.

[Darrel Taylor]

skimask,

Aw rat's, gave you a chance, but you missed it.

You were supposed to say "BAM".

Bit Angle Modulation.

For devices that rely on the "Average Current" resulting from a PWM signal, the PWM signal doesn't need to be exactly symmetrical waveforms based on consecutive ON and OFF cycles.

With BAM, you only need 8 interrupts per cycle. Each time period is "weighted" by it's bit position in the DutyCycle variable.

This way, you could turn every pin on a PIC18F8720 (all 67 of them) into PWM (BAM) outputs (at pretty high frequencies).

And of course, with DT_INTS, it's a piece of cake.
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[Acetronics2]

Hi, Malc

Some more food for your brain :

http://www.manhattancontrols.com/for...wtopic.php?t=4

Alain

[Sean_Goddard]

Why not talk to a PIC in the module using I2C?? After all, the track is two wires.

You could modulate this on top of a standing DC voltage then control a motor using hard coded addresses on the loco module PCB and an H bridge driven by the PWM from the PIC.

Just a thought. I tried it and it worked fine. Be careful of the need to filter the I2C signals HEAVILY but not so much that you lose them.

[malc-c]

Interesting concept, sort of a cross between modern DCC and traditional control. However, its not practical in this instance as the contoller is for a club layout and would mean that every member would have to have the same system installed on their own layaouts at home. Also with the scale, fiting modules to small loco's is a pain in the ***

[Acetronics2]

Hi Malc,

I Had my father home this week-end ...

We talked about supplies and it seems the today's "must" is to use switching supply during speed transitions ( or accelerations ) and DC during constant speed running ( of course for noize !!! ) ...

That meets one of Sougata's threads about signal generation with a Pic ... and opens interesting reflexion and work about what output stage to use !!!

new challenge for Darrel !!! ( He Looooooves !!!! )

Alain