Controlling servo with pic16f1789 for car backseat table

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This post is about use of servo motor in Car backseat tray system.

 Servo motor :

                                    Servo motor is a dc motor with a derive circuit and position sensor for precise movements. position sensor used in servo motor is normally potentiometer attached to gears of motor.
Derive circuit typically consists of 
  1. pulse width modulation to voltage converter
  2. feedback from potentiometer
  3. supply voltages
Feedback from position sensor is compared with converted voltage and resulted output is used to correct position of motor until both signals are equal. Servo motor will maintain its position and resist  to any external change as long as modulated pulse is present at control wire of motor.

Control signal :

                              control signal is most complex signal out of three signal required to operate DC Servo motor . Other two signals are 0 v and 5 volts out of battery. To generate control signal we are using Pic 16f1789 micro-controller in pwm (pulse width modulation ) mode.

Setting Pic 16f1789 in PWM mode :

                                                                      To configure micro-controller in pwm mode first we have to configure oscillator of  Pic 16f1789 up-to our requirements . configure oscillator to 125 KHz internal oscillator. configure device for pwm mode and interrupt on change mode. Load values of wave's period and duty cycle in pr2 and corresponding CCPRxL  registers . 

Motor used :

                         Motor used in this project is dc servo motor having rotation 0-90 degrees. 1 ms pulse for minimum rotation and 2 ms pulse for full rotation operating at 50 Hz .

Code for Controlling Servo using Pic 16f1789 :

This code is written to operate servo motor according to open/close position of control button of Car backseat tray system . you can use code under the main heading if only fixed pulse is required
  #include "p16F1789.inc"
; __config 0x2FE4
 __CONFIG _CONFIG1, _FOSC_INTOSC & _WDTE_OFF & _PWRTE_OFF & _MCLRE_ON & _CP_OFF & _CPD_OFF & _BOREN_ON & _CLKOUTEN_OFF & _IESO_ON & _FCMEN_ON
; CONFIG2
; __config 0x3EFF
 __CONFIG _CONFIG2, _WRT_OFF & _PLLEN_OFF & _STVREN_ON & _BORV_LO & _LPBOR_OFF & _LVP_ON
  ORG 000H
  GOTO MAIN
  ORG 004H
  GOTO INTERRUPT_SELECT
  ORG 020H
INTERRUPT_SELECT
  BTFSS INTCON,IOCIF
  RETFIE
  BANKSEL INLVLA
  BTFSC IOCAF,0
  GOTO OPEN_CLOSE
  NOP
  RETFIE
OPEN_CLOSE
  BANKSEL PORTA
  BTFSC PORTA,0
  GOTO OPEN
  BTFSS PORTA,0
  GOTO DEFAULT
  RETURN
OPEN
  BANKSEL ODCONA
  BCF CCP1CON,DC1B1
  BCF CCP1CON,DC1B0
  MOVLW B'00000100'
  MOVWF CCPR1L
  BANKSEL INLVLA
  BCF IOCAF,0
  RETFIE
DEFAULT
  BANKSEL ODCONA
  BCF CCP1CON,DC1B1
  BCF CCP1CON,DC1B0
  MOVLW B'00000010'
  MOVWF CCPR1L
  BANKSEL INLVLA
  BCF IOCAF,0
  RETFIE

MAIN
  BSF INTCON,GIE
  BSF INTCON,PEIE
  BSF INTCON,IOCIE
  BANKSEL ANSELA
  BCF ANSELA,0
  BANKSEL INLVLA
  BSF IOCAP,0
  BSF IOCAN,0
  BANKSEL TRISA
  BSF TRISA,0
  MOVLW B'00101000'
  MOVWF OSCCON
  CLRF OSCTUNE
  BSF TRISC,2
  BANKSEL ODCONA
  MOVLW B'00001100'
  MOVWF CCP1CON
  MOVLW B'00000010'
  MOVWF CCPR1L
  BANKSEL PORTA
  MOVLW .38
  MOVWF PR2   
  MOVLW B'00000110'
  MOVWF T2CON
  BANKSEL TRISA
  BCF TRISC,2
  BANKSEL INLVLA
  BCF IOCAF,0
HERE
  GOTO HERE
  END
  







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