Model Train controller - revisited

[malc-c]

Glug.. help ! glug glug... I'm drowning...... this is way over my head

As far as I recall Darrels routines are software PWM and not Hardware ? However having said that I have not tried all channels at the same time to control two independant tracks.....

On the subject of frequencies... when using a 4 Mhz xtal the rate at which the pulses are sent is quite noticeable at slow speed as each pulse is sent causes the model to "jump" at each step. Using a 20Mhz Xtal this is less noticable. When we were trying different settings, higher frequencies (estimated at around a few Khz ) were produced and the armature sang as the model made its way down the track.

Steve hit on the subject of a frequency higher than the ear can hear, but I'm wondering if these pulses were sent at say 30Khz, the loco would start to see them as almost a constant voltage level. Its a bit irrelevent as under the settings in Darrels code, I can't get a frequency higher than 260 hz with two channels when running the 16f767 with a 20 mhz xtal.

[mister_e]

As i said, i worry about such high frequency for this type of motor which are usually drive in 'pure-dc'. Maybe something to try... but for long term... i really can't say what could happen. One more reason why i posted a possible solution schematic... kind of linear regulation, sort of.

But first, have all your loco available and try with <300Hz. HPWM and/or SSPWM.

[malc-c]

The only thing I couldn't work out with your op amp schematic, is where the power for the motor comes from as it shows the supply connected across the motor

Smoothing capacitors across the output helps with the harshness of the PWM, and I'll try using a diode in parallel with the motor, but won't that effectively short the output to gnd ?

[mister_e]

Oh yeah, my mistake.. anyways, the power is suppose to be attach to the Op-amp and transistor Collector. This work, but it may (will) heat much.

[Acetronics2]

A look to µChip AN 1074 ... ??

Alain

[Acetronics2]

Hi, Malc

I tried to compile your project and get a strange error at compiling : PIR2 not found ...

which is the processor you use ? 767 or 676 ???
and is the posted "twin track controller" your source ???

the SPWM might run properly ...

Alain

[malc-c]

Hi,

I'm using the 16F676 - this is the code that I have (I think its the same as per the 1st post in this thread)

@ __CONFIG  _HS_OSC & _WDT_ON & _PWRTE_ON & _MCLRE_OFF 

DEFINE OSC 20

ANSEL = %00010111    			        ' Set which ports are digital and which are analogue
CMCON=7                                 ' Turm Comparitors off
TRISA=%11111111        			        ' set PORTA as all input 
TRISC=%00000001        			        ' set PORTC as all output apart from RC0

DEFINE ADC_BITS  8     			        ' ADCIN resolution  (Bits)
DEFINE ADC_CLOCK 2     			        ' ADC clock source  (Fosc/32)
DEFINE ADC_SAMPLEUS 11 			        ' ADC sampling time (uSec)

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

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

DutyVar VAR byte[4]                     ' Array used to store ADC [channels]

ASM
SPWM_LIST  macro                    	; Define Pin's to use for SPWM
    SPWM_PIN  PORTC, 2, _DutyVar        ; and the associated DutyCycle variables
    SPWM_PIN  PORTC, 3, _DutyVar+1      ; (Additional channels DutyVar+2, +3 etc)
  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, DUTYVAR[0]                    ; if having more channels add ADCIN 2, DUTYVAR[2] etc
 ADCIN 1, DUTYVAR[1]
GOTO Main                               ; program simply loops round reading ADC and sending corresponding PWM out

Compiles fine here