PMDC SERVO MOTOR WITH quadrature encoder DRIVE ?

**mackrackit** · - 29th August 2009, 14:41

Here are some threads talking about how to work with the encoder.
http://www.picbasic.co.uk/forum/show...rotary+encoder
http://www.picbasic.co.uk/forum/showthread.php?t=1552
http://www.picbasic.co.uk/forum/showthread.php?t=9700

As far as stopping goes...
Does the motor have a built in brake for holding? It can be stopped by shorting the leads but how fast it stops that way depens on the speed it is running when the leads are shorted.

**phoenix_1** · - 29th August 2009, 20:13

I was probe to stop motor and all work good.
But now I have another problem:
All examples from forum for read quadrature encoder with A and B outputs
at 5V are confused for my head, I was probe PBP examples but is to slow
and I think that for read quadrature encoder is needed ASM or some INT rutine becouse when motor work on ~ 3000 rpm rutine must be ultra speed
and background proces....
My head is like baloon ...

**phoenix_1** · - 30th August 2009, 21:19

All other info about my probe is now in PicBasicPro FORUM in:
Probe to read quadrature encoder with DT_INT need help
After my success I will post all here on FORUM.
If any help and good idea pls write.
Many thanks to all good peoples here!
Best regards Robert

**HenrikOlsson** · - 31st August 2009, 06:08

I recommend you take a look at the 18F2431 series PIC. It has a motion feedback module built in that can be set up to keep track of an incremental encoder. It also has a lot of other goodies specifically targeted at motor control applications.

/Henrik.

**phoenix_1** · - 31st August 2009, 08:32

Originally Posted by HenrikOlsson

I recommend you take a look at the 18F2431 series PIC. It has a motion feedback module built in that can be set up to keep track of an incremental encoder. It also has a lot of other goodies specifically targeted at motor control applications.

/Henrik.

I was buy today 18F4431 and will move to it.
At moment I looking for examples for it.
Thanks and regards Robert

**HenrikOlsson** · - 31st August 2009, 21:20

Hi,
This is cut and pasted from a larger program I have and this digested version is not tested so take it for what it is please. It's written for the 18F2431 so double check the pin assignments for the QEI module.

Code:

DEFINE HSER_RCSTA 90h                       'USART receive status init.
DEFINE HSER_TXSTA 24h                       'USART transmit status init.
DEFINE HSER_BAUD 57600                      'Baudrate is 57600.

ANSEL0 = 0                                  'All inputs as digital

PortA = 0
PortB = 0
PortC = 0

TRISA = %11000                           'QEI pins as inputs.
TRISB = %00000000
TRISC = %10000000                       'USART RX pin as input.

QEICON = %00010100                      'Setup QEI, 4X mode, reset on index. 

PosLow VAR BYTE                          'Storage for the low byte of encoder count
PosHigh VAR BYTE                         'Storage for the high byte of encoder count
PosTemp VAR BYTE                        'Temporary storage for low byte of encder count
Position VAR WORD                        'Actual encoder position, 16bit word.

CLEAR

Main:
  Gosub GetPosition
  HSEROUT ["QEI Count: " , #Position, 10]
  Pause 100
Goto Main

GetPosition:
'Since the position counter isn't double buffered we can get to situations
'where the lowbyte overflows between readings of the high and the low byte. This
'is prevented by reading the low byte two times and compare the two readings.
'If they are the same then we're fine, if not re-read the registers.
  
    PosHigh = POSCNTH                       'Get high byte of counter
    PosLow = POSCNTL                        'Get low byte of counter
    PosTemp = POSCNTL                       'Get low byte again
    
    If PosLow - PosTemp = 0 then Goto Done      'Compare, if equal we're done.
    
    PosHigh = POSCNTH                           'If not, get values again.
    PosLow = POSCNTL

Done:
    Position = POSHIGH * 256 + PosLow           'Put high and lowbyte together.
RETURN
END

Again, no guarantees but I hope it serves as a starting point for you.

/Henrik.

**mackrackit** · - 31st August 2009, 22:07

Hi Henrik,

I started playing with the 4431 DIP version and wonder if you have ran into this with the one you are using. Maybe it is a 4331 problem, maybe whole series.

When using a 4Mhz resonator and have the config set for HSPLL and DEFINE OSC 16 all works well.

If I replace the 4Mhz with a 10 Mhz and try DEFINE OSC 40 everything goes erratic.
The PIC runs but even a simple "blinky" will blink randomly.

Here is the very simple code and configs I was playing with to set the OSC.

Code:

    @ __CONFIG    _CONFIG1H, _OSC_HSPLL_1H
    @ __CONFIG    _CONFIG2H, _WDTEN_ON_2H & _WDPS_512_2H
    @ __CONFIG    _CONFIG2L, _BOREN_OFF_2L & _PWRTEN_ON_2L    
    @ __CONFIG    _CONFIG3H, _MCLRE_OFF_3H
    @ __CONFIG    _CONFIG4L, _LVP_OFF_4L  
    
     DEFINE OSC 16
     
    START:HIGH PORTD.1:PAUSE 500
    LOW PORTD.1:PAUSE 500:GOTO START

**phoenix_1** · - 31st August 2009, 22:58

Originally Posted by HenrikOlsson

Hi,
This is cut and pasted from a larger program I have and this digested version is not tested so take it for what it is please. It's written for the 18F2431 so double check the pin assignments for the QEI module.

Code:

DEFINE HSER_RCSTA 90h                       'USART receive status init.
DEFINE HSER_TXSTA 24h                       'USART transmit status init.
DEFINE HSER_BAUD 57600                      'Baudrate is 57600.

ANSEL0 = 0                                  'All inputs as digital

PortA = 0
PortB = 0
PortC = 0

TRISA = %11000                           'QEI pins as inputs.
TRISB = %00000000
TRISC = %10000000                       'USART RX pin as input.

QEICON = %00010100                      'Setup QEI, 4X mode, reset on index. 

PosLow VAR BYTE                          'Storage for the low byte of encoder count
PosHigh VAR BYTE                         'Storage for the high byte of encoder count
PosTemp VAR BYTE                        'Temporary storage for low byte of encder count
Position VAR WORD                        'Actual encoder position, 16bit word.

CLEAR

Main:
  Gosub GetPosition
  HSEROUT ["QEI Count: " , #Position, 10]
  Pause 100
Goto Main

GetPosition:
'Since the position counter isn't double buffered we can get to situations
'where the lowbyte overflows between readings of the high and the low byte. This
'is prevented by reading the low byte two times and compare the two readings.
'If they are the same then we're fine, if not re-read the registers.
  
    PosHigh = POSCNTH                       'Get high byte of counter
    PosLow = POSCNTL                        'Get low byte of counter
    PosTemp = POSCNTL                       'Get low byte again
    
    If PosLow - PosTemp = 0 then Goto Done      'Compare, if equal we're done.
    
    PosHigh = POSCNTH                           'If not, get values again.
    PosLow = POSCNTL

Done:
    Position = POSHIGH * 256 + PosLow           'Put high and lowbyte together.
RETURN
END

Again, no guarantees but I hope it serves as a starting point for you.

/Henrik.

What if my ENCODER have only A and B output's and dont have INDEX pin ?
Can I use it ???

**phoenix_1** · - 3rd September 2009, 06:50

Here is success probe with count encoder from 0 to 2000 for one turn of shaft of motor.

Code:

' Pic 18F4431 @ 20MHz true XTAL
    define osc 20
    DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
    DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
    DEFINE HSER_SPBRG 64  ' 19200 Baud @ 20MHz, 0.16%
    DEFINE HSER_CLROERR 1 ' Clear overflow automatically
    ADCON0=0 'Turn of ADC
    ANSEL0=0 'Make Port A inputs Digital

    PortA = 0
    PortB = 0
    PortC = 0

    TRISA = %011100                'QEI pins as inputs.
    TRISB = %00000000
    TRISC = %10000000              'USART RX pin as input.

    QEICON=%11001100
    DFLTCON = %00111000            ' enable error filter for all capture inputs
    MAXCNTL = %11001111           'lowbyte = 207
    MAXCNTH = %00000111           'highbyte = 7 but after math: highbyte * 256 = 1792 + 207 = 1999
'QEICON = %00010100                   'Setup QEI, 4X mode, reset on index. 
    PosLow VAR BYTE                          'Storage for the low byte of encoder count
    PosHigh VAR BYTE                         'Storage for the high byte of encoder count
    PosTemp VAR BYTE                        'Temporary storage for low byte of encder count
    Position VAR WORD                      'Actual encoder position, 16bit word.
    POSCNTL = 0                            ' clear lowbyte of counter for start
    POSCNTH = 0                            ' clear highbyte of counter for start
CLEAR
    
Main:
    Gosub GetPosition
    HSEROUT [dec position]
    Pause 100
Goto Main

GetPosition:
'Since the position counter isn't double buffered we can get to situations
'where the lowbyte overflows between readings of the high and the low byte. This
'is prevented by reading the low byte two times and compare the two readings.
'If they are the same then we're fine, if not re-read the registers.
  
    PosHigh = POSCNTH                       'Get high byte of counter
    PosLow = POSCNTL                        'Get low byte of counter
    PosTemp = POSCNTL                       'Get low byte again
    
    If PosLow - PosTemp = 0 then Goto Done      'Compare, if equal we're done.
    
    PosHigh = POSCNTH                           'If not, get values again.
    PosLow = POSCNTL 

Done:
    Position = POSHIGH * 256 + PosLow           'Put high and lowbyte together.
RETURN
END

Will continue...
Robert

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