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Wura Guest
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Motor Control |
Posted: Mon Mar 27, 2006 7:46 pm |
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I am using the PIC 16F874, I am trying to change the direction of a DC motor by simple interupt switches. I am outputing to an L272 chip which drives the motor and accepts two logic inputs. A C0 of one and C1 of zero puts a postivive voltage on the motor and a C0 of zero and C1 one should but a negative voltage on my motor. The L272 chip works fine independently of the PIC and the PIC works fine without connecting to the L272 chip. When I hook them together I can only get the motor to run in one direction.
Please can you take a look at my code and see if i am doing something wrong.
#include <16F874.H>
#use delay(clock=20000000)
char event;
void main()
{
enable_interrupts(INT_rb);
enable_interrupts(global);
// Initializing default values
event = 'r';
while(event == 'r')
{
//motor forward
output_low(PIN_C1);
output_high(PIN_C0);
}
while(event == 'g')
{
output_high(PIN_C1);
output_low(PIN_C0);
}
}
#int_rb
rb_isr ( )
{
// Initializing everything
byte changes;
int last_b;
int port_b;
changes = last_b ^ port_b;
last_b = port_b;
// if wheel has went one complete revolution
if (!input(PIN_b7)){event = 'r';}
// if bob hit grain
if (!input(PIN_b6)){event = 'g';}
// if bob is at housing
if (!input(PIN_b5)){event = 'h';}
//debounce
delay_ms(100);
} |
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SherpaDoug
Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA
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Posted: Tue Mar 28, 2006 7:21 am |
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What direction does the motor spin in? What are the logic lines doing when the motor is spinning the wrong way? Can you put a meter, or better yet a scope on them? Is the motor putting noise on the PIC power line? _________________ The search for better is endless. Instead simply find very good and get the job done. |
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Ttelmah Guest
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Posted: Tue Mar 28, 2006 7:49 am |
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The first few lines of the interrupt handler do nothing. You need to declare 'last_b', as a _static_ variable, or it's contents may be lost between interrupts. Also the code looks as if it was an attempt to see the port bit changes (in which case, 'port_b', wants to actually be the 'port', rather than a normal variable. As a second general comment _get rid of the delay in the interrupt handler_...
I'd suspect the code actuall wants to be:
Code: |
#int_rb
void rb_isr(void) {
// Initializing everything
byte changes;
static int last_b;
int port_b;
//Read the port - this resets the 'port changed' latch
port_b=input_b();
changes = last_b ^ port_b;
last_b = port_b;
// if wheel has went one complete revolution
if (changes & 0x80) {
//Here the revolution detector has _changed_. Check now it has fallen.
if (!(port_b & 0x80)) event = 'r';
}
// if bob hit grain
if (changes & 0x40) {
if (!(port_b & 0x40)) event = 'g';
}
// if bob is at housing
if (changes & 0x20) {
if (!(port_b & 0x20)) event = 'h';
}
}
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As a seperate comment, if you need a huge delay like 100mSec, then program a hardware timer, and check the bits again when this has expired.
Also, look carefully at your 'event' codes. What happens if two edges trigger together?. You will 'lose' the first edge that you test for. Consider instead using an event 'mask'. So:
#define HOUSING (4)
#define GRAIN (2)
#define REV (1)
Then when you detect an event, _or_ the current event code, with the value for this event. In your main 'test', test for the event '&' the required code, and once handled, clear this code. This way the system can respond to more than one event.
Best Wishes |
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