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sooryakrishnan.u
Joined: 20 Jan 2016
Posts: 1
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| HCSR04 Ultrasonic sensor with pic 16f877a |
 Posted: Wed Jan 20, 2016 12:50 am |
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Hi i am using HCSR04 Ultrasonic Sensor with PIC16F877A for obstacle detection. I just need to count the no of incoming and outgoing people in my project. But the issue is that i am not receiving anything in my teraterm.
This is the code i wrote. Here i have just used one hcsr04 for clarity. Can any one point me out where i have gone wrong?
| Code: |
#include <16F877A.h>
#device ADC=16
#FUSES NOWDT //No Watch Dog Timer
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOLVP //No low voltage prgming, B3(PIC16) or B5(PIC18) used for I/O
#use delay(crystal=20000000)
#use STANDARD_IO( A )
#use rs232(baud=9600,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,stream=PORT1)
#define TRIG PIN_A0
#define ECHO PIN_B4
/****************************************/
unsigned int count = 0;
#INT_RB
void RB_isr(void)
{
count++;
}
void main()
{
delay_ms(3000);
setup_timer_1(T1_INTERNAL|T1_DIV_BY_8); //104 ms overflow
enable_interrupts(INT_RB);
enable_interrupts(GLOBAL);
while(TRUE)
{
output_low(ECHO);
output_low(TRIG);
delay_us(5);
output_high(TRIG);
delay_us(10); // sending 10us pulse
output_low(TRIG);
while(input(ECHO)) // Wait for high state of echo pin
{}
printf("Count = %u",count);
}
} |
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Code block added.
- Forum Moderator
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Ttelmah
Joined: 11 Mar 2010
Posts: 19327
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| Posted: Wed Jan 20, 2016 2:11 am |
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First learn to use the code buttons...
Then without looking at anything else in the code, there is a critical problem. You _must_ read portB, inside the INT_RB handler.
INT_RB, is an 'interrupt on change'. It goes 'TRUE', whenever portB, differs from the portB 'latch'. The latch is set to the current portB status, when the port is read.
Now this means that if the portB interrupt triggers, and you don't read the port (to reset the latch), it'll immediately trigger again. So effectively the INT_RB handler can never exit....
There are a number of interrupts like this. INT_TBE for instance, will keep triggering, until you load something into the transmit buffer. INT_RDA, will keep triggering until you read the receive buffer.
In the cases of interrupts like this, you must clear/handle what the interrupt is set to trigger on, before you exit the interrupt handler. The compiler will clear the interrupt flag, but it immediately gets set again....
So in your code at present, INT_RB triggers, and the handler can then never exit, so the rest of the code stops working.  |
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