Obstacle detection using an ultrasonic sensor and a PIC microcontroller

Question

I'm trying to detect obstacles at a specific distance using an ultrasonic sensor which is interfaced with a PIC micro controller.

• Ultrasonic sensor = HC-SR04
• PIC micro controller = PIC16F628A

This will turn on a LED when an obstacle placed in front of the ultrasonic sensor at a specific distance or distance less than that. In order to do that I have written the following assembly code. But it doesn't seems to be working as expected. The LED doesn't lit for any distance.

Here is the assembly code

PROCESSOR PIC16F628A
#INCLUDE <P16F628A.INC>
#INCLUDE <BANKSEL.INC>
CBLOCK 0x20 ; DEFINE VARIABLES USED
C1 
d1
d2
d3
ENDC
ORG 0x00 ;RESET VECTOR
GOTO MAIN
MAIN
Bank0 ;goto bank0
CLRF PORTA ;Initialize PORTA by setting output data latches
MOVLW 0x07 ;Turn comparators off and
MOVWF CMCON ;enable pins for I/O functions
Bank1
bsf TRISA,7 ;set RA7 as input (ECHOIN)
BCF TRISA,1 ;SET RA1 AS OUTPUT (LED)
BCF TRISA,0 ;SET RA0 AS OUTPUT (TRIGGER PULSE)
;CLRF TRISB ;PORTB pins defined as outputs
CLRF C1 ; NOW C1 VALUE IS '00000000'
Bank0
MOVLW b'00000000' ; CLEAR W REGISTER INITIALLY
LOOP
CALL TRIG ;START TRIGGER PULSE
BTFSC PORTA,7 ;CHECK ECHO OUT PIN STATE
GOTO COUNT ;ECHO OUTPUT IS HIGH
CALL CHECKCOUNT ; THIS WILL CHECK THE VALUE IN C1
GOTO LOOP 
COUNT ;THIS WILL COUNT THE TIME LENGTH OF ECHO PULSE
INCF C1,1 ;INCREASE C1 VALUE BY 1, SAVE IT IN C1
CALL DELAY ;1mS DELAY
GOTO LOOP
CHECKCOUNT ;THIS WILL CHECK THE 7TH BIT OF C1 REGISTER
BTFSC C1,7 ;IS 8TH BIT FILLED?
GOTO LEDON ;YES
BCF PORTA,1 ;NO
L1
CLRF C1 ;CLEAR REGISTER TO WRITE NEXT COUNTED VALUE
RETURN
LEDON
BSF PORTA,1
GOTO L1
TRIG ;THIS WILL CREATE 10uS TRIG PULSE AT RB2 PIN WHICH IS CONNECTED TO TRIG PIN
 ; OF THE SENSOR
BSF PORTA,0
CALL DELAY10US
BCF PORTA,0
CALL DELAY60MS ;AVOID CREATING PULSE IN t<50MS
RETURN
DELAY
; Delay = 0.001 seconds
; Clock frequency = 4 MHz
; Actual delay = 0.001 seconds = 1000 cycles
; Error = 0 %
 ;998 cycles
 movlw 0xC7
 movwf d1
 movlw 0x01
 movwf d2
Delay_0
 decfsz d1, f
 goto $+2
 decfsz d2, f
 goto Delay_0
 ;2 cycles
 goto $+1
RETURN
DELAY10US
; Delay = 1e-006 seconds
; Clock frequency = 4 MHz
; Actual delay = 1e-006 seconds = 1 cycles
; Error = 0 %
 ;1 cycle
 nop
RETURN
DELAY60MS
; Delay = 0.06 seconds
; Clock frequency = 4 MHz
; Actual delay = 0.06 seconds = 60000 cycles
; Error = 0 %
 ;59998 cycles
 movlw 0xDF
 movwf d1
 movlw 0x2F
 movwf d2
Delay_1
 decfsz d1, f
 goto $+2
 decfsz d2, f
 goto Delay_1
 ;2 cycles
 goto $+1
RETURN
END

Are there any modifications to do in this code to make it work properly? Or has anyone got a simpler code than this to do a this kind of job? Thank you

• nidhin: What is the output you are getting? nothing ? or a wrong one?
• nrnw: The LED never turns on
• Dmitry: what kind of a sensor are you using?

Answer 1

You are checking for a delay of 128ms or more. According to the equation given in the manual here , distance measured will be 21m which is way beyond the maximum range of the module as given in the same document. In my experience, the module did not return any pulse if there's no obstacle in the measurable range.