Recommendations - Model Train Controller

[Darrel Taylor]

I assume that using a 100 Hz frequency for the PWM would be ideal... what PIC did you use, and is having an internal clock an issue (I'm using a 12F675 for experimential use)

Malcolm,

I was using a 16F877A, I guess it was really comparing Apples to Oranges.

I figured I better check with a 12F675, but didn't have one handy so I used a 12F683. It was close enough to figure out what was wrong.

This get's everyone, so I should have seen it right away, but nope.

CMCON = 7 ; disable the comparators
ANSEL = 1 ; AN0 is analog, rest digital

also, You have a PWM output on GPIO.0 ... The same pin as the POT is connected to on AN0. That'll cause problems with the A/D reading.

Hope you're still interested?

EDIT: 100hz is no problem. But you'll need a faster crystal/resonator
INTRC won't cut it.

HTH,

[malc-c]

Darrel,

Sorry I missed that... I've remmed out the PWM line fro GPIO.0 and have got a reasonable result, especially for slow speed - The crawling speed of an 18 year old tank loco is really amaizing !!

Here's the code

DEFINE OSC 20
CLEAR

DEFINE ADC_BITS 8	' Set number of bits in result
DEFINE ADC_CLOCK 3	' Set clock source (rc = 3)
DEFINE ADC_SAMPLEUS 50	' Set sampling time in microseconds

INCLUDE "DT_INTS-14.bas"            ; Base Interrupt System
INCLUDE "SPWM_INT.bas"              ; Software PWM module

DEFINE SPWM_FREQ  100                ; SPWM Frequency
DEFINE SPWM_RES   256               ; SPWM Resolution

D var byte

DutyVars   VAR BYTE[3]              ; DutyCycle Variables
  ;DutyVar1 VAR DutyVars[0]          ; group them in an array for easy access
  ;DutyVar2 VAR DutyVars[1]          ; with FOR loops etc.
  DutyVar3 VAR DutyVars[2]

ASM
SPWM_LIST  macro                    ; Define Pin's to use for SPWM
    ;SPWM_PIN  GPIO, 0, _DutyVar1  ; and the associated DutyCycle variables
    ; SPWM_PIN  GPIO, 1, _DutyVar2  ; Notice the underscore before variables
     SPWM_PIN  GPIO, 2, _DutyVar3
  endm
  SPWM_INIT  SPWM_LIST              ; Initialize the Pins
ENDASM

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,  SPWMhandler,  ASM,  yes
    endm
    INT_CREATE                      ; Creates the interrupt processor
ENDASM

@ INT_ENABLE  TMR1_INT              ; enable Timer 1 interrupts

;_____________________________________________________________________________

Main:                               
 ADCIN 0, D 
    DutyVar3 = D   
GOTO Main

Using a close loop fedback output stage and a 12v regulated supply for the track as per the diagram attached, I get a nice smooth slow speed control. This is using the 12F675 with its internal osc.

The loco does growl a bit when at really slow speed... and at maximum speed its fine for a goods train, but not an express. I susspect that using a higher track supply voltage will resolve the speed issue (my DVM reads 6.5v across the track at full speed), but wondered if there was anything I could do to reduce the growling at slow speed.

Please bear in mind that I'm still somewhat new to PICs and programming.. so If I've still overlooked something in the settings then please advise what I did wrong and how to correct it.

[Darrel Taylor]

Hmm, I don't see the CMCON and ANSEL in your program.

There's a R-M-W (Read-Modify-Write) problem when OUTPUTting to a pin set to Analog. It adds a high frequency component to the PWM signal.

I don't know if that's what is causing the growling or not.

6.5V at full speed? That doesn't sound right. The current is getting limited somewhere. Maybe if you increased the value of R4 ????
<br>

[malc-c]

Hmm, I don't see the CMCON and ANSEL in your program.

There's a R-M-W (Read-Modify-Write) problem when OUTPUTting to a pin set to Analog. It adds a high frequency component to the PWM signal.

Would the following be correct

TRISIO.2 = 0   'Set GPIO.2 to output.
ANSEL.2 = 0    'Set GPIO.2 to digital		
GPIO.0 = 1      'gpio.0 set to input
VRCON = 0        ' Voltage reference disabled
OPTION_REG.7 =    0

6.5V at full speed? That doesn't sound right. The current is getting limited somewhere. Maybe if you increased the value of R4 ????

I'll try that and see what happens, thanks for the suggestion

[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

[malc-c]

There's a R-M-W (Read-Modify-Write) problem when OUTPUTting to a pin set to Analog. It adds a high frequency component to the PWM signal.

That's interesting... whilst I was reading up on the use of your code I could hear this high pitched (estimated 4 - 8 Khz) faint sound like you often hear eminating from a TV... placed my ear near the loco (which is standing still on the track) and its singing away !!

I presume that this is due to the fact that GPIO.2 is still set to analogue and not digital ??

What config settings should I use for CMCON and ANSEL to resolve this ?

[mister_e]

in theory the right setting have to be

ANSEL=%00110001
CMCON=7
GPIO=0
TRISIO=1

and later i just change the main loop to...

Main:                               
        ADCIN 0, DUTYVAR3
        GOTO Main

AND NOW it's working pretty good and smooth... well here...

For once i found a use of the Left-Justified results... Never thought ADCIN handled it

Make sure your Pot impedance meet the maximum recommended on.. 2.5 k if my memory serves me well. 10K here (EasyPic 4) still work fine..

Also, as the ADC results is a 8 bit result, you should change the SPWM_RES to 255.

[malc-c]

Steve, Thanks for your input. I made the changes you suggested and the performance is still great and the growling sound produced by the PWM in the armature appears less noticable. The high pitched sound is still noticable, but nothing appears hot

[mister_e]

Unfortunately i don't have anything like that here to test, but Maybe the PWM have to be smooth first...

what happen if you place a big capacitor (470 & up) in parallel with the motors?

What happen if you place a capacitor (few uF) on the mosfet gate pin? (transistor base)

What happen if you use a variable voltage regulator (or PSU)? instead of PWM?