Model Train controller - revisited

[Acetronics2]

Hi, Malc

Try this:

TEMP var WORD

Main:

ADCIN 0, DUTYVAR[0] ; if having more channels add ADCIN 2, DUTYVAR[2] etc

TEMP = DUTYVAR[0] * DUTYVAR[0] / 256 '********************

IF DUTYVAR[0] < 10 THEN ' 10 = value for a neat motor start , if needed !

DUTYVAR[0] = 0
GOTO Jump0

ENDIF

DUTYVAR[0] = TEMP MAX 10

Jump0:


ADCIN 1, DUTYVAR[1]

TEMP = DUTYVAR[1] * DUTYVAR[1] / 256 '********************

IF DUTYVAR[1] < 10 THEN ' 10 = value for a neat motor start ,if needed !


DUTYVAR[1] = 0
GOTO Jump1

ENDIF

DUTYVAR[1] = TEMP MAX 10

Jump1:

GOTO Main ; program simply loops round reading ADC and sending corresponding PWM out

That what I use for my boat speed controllers ... works really fine !!!

Regards
Alain

PS: here is the original

'************************************************* *****************************
'Mise à l'echelle 0 - 255 de la sortie PWM pour 0 - 96 % de la course
'************************************************* *****************************

' 265 = 255 / 0.96 ... CQFD

'************************************************* *****************************
'Moteur Gauche
'************************************************* *****************************

EcartGazG = ( ABS ( PulsGazG - MidGaz)) ' for fwd/rev on the same stick

IF EcartGazG < 55 THEN 'Center Deadband
PowerG = 0
GOTO MotD
ENDIF

dummy = EcartGazG * 265
PowerG = DIV32 CourseGaz

PowerG = (PowerG + 1 ) MIN 255 ' 255 value as MAXI for PWM

'************************************************* *****************************
'Variation exponentielle
'************************************************* *****************************

dummy = PowerG * PowerG
PowerG = DIV32 255

'************************************************* *****************************
'Puissance mini appliquee au moteur - démarrage franc ( 20/255 )
'************************************************* *****************************

PowerG = PowerG MAX 20

[malc-c]

Guys, thanks for the replies.

To answer some of the questions, yes the pots are lin, or at least they are marked as lin and purchased as such, and using a DVM it seem that they are liniar. I'll look at taking all the unused pins to +ve, possibly via 10k resistors.

Alain,

I think that the original code above basically works on the same principle of taking the 0 - 254 from the adc and sending that out as the pulse. However it all got a bit complicated when Darrel's routines were used as all I know is that i need to do is change then two values

DEFINE SPWM_FREQ  150                	' SPWM Frequency (Hz)
DEFINE SPWM_RES   254               	' SPWM Resolution (0 - 255)

I'll try adding your code and will report back

[mister_e]

The LOG pot is a nice idea, Alain's routine too. You can also build a huge LOOKUP table with excel and read from it. If you have some VCA (like ssm2164) you can use a Linear pot and get a LOG curve.

Many different ways.

At least, there's some progress

PS: you can trick the curve a little bit by adding a resistor in parrallel with the wiper... far to be LOG, but could be interesting to trace the curve...

THE PWM freq shouldn't affect the results... shouldn't..

[malc-c]

Well it compiles Ok and it does indeed work, providing a better range of travel for the lower end of the POT. It produces an interesting wave form

The only problem is that oscilatons produce noise in the loco's armature. I tried the old trick of using a capacitor across the output which worked to some degree, but as it effectivly smoothed the pulses it defeats the object of using PWM (or PPM)

Steve, I'll try your suggestion

[malc-c]

Oh and one other thing I've noticed,which may be causingn the PIC to bomb is when the when the wiper is at the top and thus connected to the 5.21v supply the pulses stop and the voltage out drops, and on some occasions this has caused the driver to sort of lock as moving the pot after the effect has no effect as the PMW generation has stopped. Is there a way of setting the voltage ref or ADC value so that a PMW signal is always produced ?

Edit:
maybe this video might help explain (2.2 MB Divx format) http://www.micro-heli.co.uk/scope4.avi

[mister_e]

The weird results you have is probably caused by the delay to do the calc... well i think.

Don't try the Resistor... i was 100% wrong.. it's not going to be LOG... just alog... as per i got from EXCEL... so just worst than before

<img SRC="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1557&stc=1&d=117726977 2">

oops, it's sunday

...mmm something to do anyway with that... scratch scratch...

[mister_e]

What happen to your PWM lock-up thingy if you replace the Motor by a resistor? I don't see any back EMF diode here...

EDIT: check the maximum range of your scalling maths

EDIT2: well it's really sunday !!

However, the amount of rotation of the pot is quite small before the loco is up to a medium speed.

so if i'm right... the curve above should work?

do i need to sleep or get another brain? I've attach my noobie-style excel sheet.

Just play with the Value in D1 cell and enjoy.

[malc-c]

Hi again Steve,

The EMF feedback was removed following a suggestion from Alain in the original thread ( http://www.picbasic.co.uk/forum/show...0&postcount=46 )

Could you elaborate on the scaling thing...

I'll have a play with the speadsheet and add a few resistors in parallel to see what happens. It will probably won't be tonight as I don't have access to the loco anymore (It shot off the end of the test track and now boxed up as it is in need of repair, and my son has gone to bed now so I can't get one of the other locos !)

Sorry guys for going over this again, but I still cant get my head round some of these aspects of programming.