Recommendations - Model Train Controller

[Acetronics2]

Hi, Malc

I do not know where you found R4 and D1 ... but your problems come from there.

No real use for them ... so, back to their drawer will be the best.

... or use another Pic pin if you want to do something with the freewheel emf !!!

a simpler output stage would be welcome ( your NPN Emitter to ground and a series 1 k in the base connection i.e. )

Alain

[malc-c]

Alain,

Thanks for the suggestion... the output circuit was taken from a book and is actually a cloose-loop feedback controller... I just fed the output from the PIC directly to the base of the NPN tranny... but I'll try your suggestions and see if it improves the max speed settings. However in its current state it makes for an excellent branch line controller where slower trains would run...

To give you some idea of the excellent slow speed the PWM gives have a look at this video I've uploaded http://www.micro-heli.co.uk/controller.avi (9mb DIVx format)

[malc-c]

Omitting the feedback section (R4 and 1N4148), and adding a 1K base resistior I now get a good range of speed and excellent slow speed crawling. Just need to resolve the growling in the armature

[Acetronics2]

Hi, Malc,

The only way is to increase the PWM frequency ( 500 or 1000 Hz might be enough ).
also Think to the minimum PWM ratio zone to skip ( ~ 10 % )

you'll find a problem here : some motors do not like high frequencies ( > 3000 Hz ) due to their high inductance ... and might overheat.

Do you think I could make a test with my Big Boy, die cast "crocodile" or JEP 231 ... or some oldies ???

Hé,hé ... my father gave its life and brain to our national railway company ...and still builds custom models ( 84 years ...the papy !!! )

Alain

[malc-c]

Well I've been playing with the values for SPWM frequency and resolution and found the highest setting for the 12F675 using internal osc was around

DEFINE SPWM_FREQ  200                ; SPWM Frequency
DEFINE SPWM_RES   256               ; SPWM Resolution

Its not possible to up the resolution without using an external OSC. However I intend to use a different PIC and may opt to use it at is max xtal rating, especially if I use the one PIC to provide all 4 channels. Maybe the higher resolution will reduce the grumbling in the armature... mind you if this was on old 0-6-0 shunter it would look and sound just right

One thing I did notice is that when using the PWM version the power tranny runs cold, where with the close loop version it warmed up (slightly)

Anyway, I'm having fun learning