Recommendations - Model Train Controller

[malc-c]

hopefully the attached image will try to get over my idea. By adjusting VR1 the resulting value is used to adjust the PPM output on RB0 which (via the power tranny) is fed to the tracks.

[mister_e]

I would use PNP over NPN for that... Depending the current needed, Some P-Channel mosfet.

[Acetronics2]

Driving a '3055 straight from the PIC port ...

Interesting idea ...

Alain

[malc-c]

The diagram was for example only, I intend to use FETs for the driver (They work fine driven directly from a PIC) - If I was going to use a 3055 I would use a GP NPN tranny and connect the two in an emitter follower fashion.

I'm really after your comments on using a PIC's A/D to control the output PW modulation..

[Acetronics2]

Hi, Malc

Why not simply use RCTime to read your pots ...

That would allow "simple" pics like '84 or '628 ... even 648 !!! ... just because of the pincount !!!

Alain

[malc-c]

Alain,

One step ahead of you... I'm using a 16F828a and set up a 100K lin pot and 0.1uf capacitor, and a simple bit of code.. but can't get it to work (just slung it together in the past 5 mins)

The code compiles, but I don't get any PWM on the output (using a LED for test purposes at the moment - no FET connected.)

10k between MCLR and +5v, input from the pot to A2

Here's the code

;************ set up PIC *****************
PORTA = 0                        ' declare port level BEFORE port direction = safe power-on
CMCON = 7                        ' PortA Digital inputs
CCP1CON = 0                      ' PWM off
VRCON = 0                        ' Voltage reference disabled
OPTION_REG.7 =    0


TRISA=%11101111                  'set PORTA as all input apart from A4
TRISB=%00000000                  'set PORTB as all output

@RC_OSC_NOCLKOUT 
@WDT_ON
@PWRT_ON
@MCLR_OFF
@BOD_ON
@LVP_OFF
@CPD_OFF
@PROTECT_OFF

;************* set up varibles ************
    
D var byte                          ;used to store the result of the pot on port A2
scale var byte                      ;used in the POT command
Scale = 254                         ;used to set range 
                                                            
;************* main program ****************
Main:                         
Pot PORTA.2,scale,D                 ;used to read value from pot
pwm PORTB.4,D,1
Goto main

The main loop is self explanatory, port A2 is checked and the result is placed in the variable D, this is used to set the width of the PWM sent out on pin B4

Any ideas why I can't get it to work

[mister_e]

Malc,
Your configuration fuse don't do anything. The way you do it, it actually do nothing else than define some Labels.

        '
        '       PIC Configuration fuses
        '       =======================
                '    _BODEN_ON 
                '    _BODEN_OFF
                '    _CP_ALL   
                '    _CP_75    
                '    _CP_50    
                '    _CP_OFF   
                '    _DATA_CP_ON 
                '    _DATA_CP_OFF
                '    _PWRTE_OFF  
                '    _PWRTE_ON   
                '    _WDT_ON     
                '    _WDT_OFF    
                '    _LVP_ON     
                '    _LVP_OFF    
                '    _MCLRE_ON   
                '    _MCLRE_OFF  
                '    _ER_OSC_CLKOUT 
                '    _ER_OSC_NOCLKOUT 
                '    _INTRC_OSC_CLKOUT 
                '    _INTRC_OSC_NOCLKOUT 
                '    _EXTCLK_OSC         
                '    _LP_OSC             
                '    _XT_OSC             
                '    _HS_OSC 
        @ __CONFIG  _INTRC_OSC_NOCLKOUT & _MCLRE_OFF  &  _LVP_OFF & _WDT_ON & _PWRTE_ON  & _BODEN_ON

[Acetronics2]

Alain,

One step ahead of you... I'm using a 16F828a and set up a 100K lin pot and 0.1uf capacitor, and a simple bit of code.. but can't get it to work (just slung it together in the past 5 mins)

pwm PORTB.4,D,1
4

Any ideas why I can't get it to work

Hi, Malc

1) May be you should try the HPWM function ... i've noticed it worked much better for motor PWM ... on PORTB.3 instead of B.4 ( ! )

2) Try RCTime ...instead of this stupid POT ... linearity will be far better !!!

AND KEEP WITHIN THE MANUAL VALUES ( 5 -50 k ; 0.1µF ) IF STILL USING POT !!!

heuuuu ... your scale value (254 ) is a bit surprising ...

Alain