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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| Controlling LCD flicker |
 Posted: Thu Oct 20, 2005 4:56 pm |
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I've been playing around with a program that I cobbled together from various sources on the internet. It reads a digital rangefinder and outputs the value to an LCD.
The problem is that the LCD image flickers quite badly. Two changes I've made, based on what I've read in the archives, have had some effect.
1. Introducing a 1/2 second delay in the data refresh rate helped but still left a little flicker. I would prefer not to have any delay at all.
2. Moving the LCD_INIT () statement out with the WHILE(1) statement didn't help and it actually removed my first line on the LCD.
Here is a sample of the code; the relevent portion is in the bottom 20 lines.
| Code: |
#include <16F628.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#include <LCD_4LINE.c> //this file set up to use port B
#define GP2D02_VIN PIN_B3
#define GP2D02_VOUT PIN_A2
set_tris_a(0xff);
set_tris_b(0x00);
int reading;
int get_ir_reading();
int get_ir_reading()
{
int counter=9;
int reading=0;
output_low(GP2D02_VIN); // start cycle with Vin low
delay_ms(1); // give the sensor a little time before we bug it
while (!input(GP2D02_VOUT)); //wait for Vout to go high
do {
delay_cycles(4); // minimum wait is 2us, max is 170us, 4 worked
output_low(GP2D02_VIN); // tell the sensor that we want a bit
delay_cycles(2); // might be as low as 1 (maybe), 2 worked
reading=reading<<1; // left shift the reading value
reading=reading|(input(GP2D02_VOUT)); // put the newest reading into the
// LSB of reading
output_high(GP2D02_VIN); // we read bit, and get ready for the next one
counter--;
} while (counter>0);
printf(lcd_putc,"\f IR Measurement");
printf(lcd_putc,"\n================");
lcd_gotoxy(1,3);
printf(lcd_putc,"Value =%u",reading);
lcd_gotoxy(1,4);
printf(lcd_putc,"Distance =");
delay_ms(500);
return(reading);
}
void main()
{
while(true)
{
lcd_init();
get_ir_reading();
}
}
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Any ideas on how I might be able to further reduce the flicker?
Thanks....Harry |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Oct 20, 2005 5:13 pm |
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The reason it's flickering is because you're continuously clearing the
screen. You've got "\f" in there:
| Quote: | | printf(lcd_putc,"\f IR Measurement"); |
You shouldn't have to continuously re-init the LCD. If you have
to do that, then something is wrong.
Also your code as posted won't compile. You have a couple
floating set_tris statements. |
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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| Posted: Thu Oct 20, 2005 7:23 pm |
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Thanks, that was the problem. I was also able to make the changes suggested in the archives. A couple of things:
1. It does compile. I don't know what floating set_tris statements are.
2. When the variable "Reading" goes under a hundred, the value displayed on the LCD goes to three digits. For example 99 becomes around 999, etc. I assume it has something to do with the bit shifting done withing the get_IR_reading function.
Here is the new code:
| Code: |
#include <16F628.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#include <LCD_4LINE.c> //this file set up to use port B
#define GP2D02_VIN PIN_B3
#define GP2D02_VOUT PIN_A2
set_tris_a(0xff);
set_tris_b(0x00);
int reading;
int get_ir_reading();
int get_ir_reading()
{
int counter=9;
int reading=0;
output_low(GP2D02_VIN); // start cycle with Vin low
delay_ms(1); // give the sensor a little time before we bug it
while (!input(GP2D02_VOUT)); //wait for Vout to go high
do {
delay_cycles(4); // minimum wait is 2us, max is 170us, 4 worked
output_low(GP2D02_VIN); // tell the sensor that we want a bit
delay_cycles(2); // might be as low as 1 (maybe), 2 worked
reading=reading<<1; // left shift the reading value
reading=reading|(input(GP2D02_VOUT)); // put the newest reading into the
// LSB of reading
output_high(GP2D02_VIN); // we read bit, and get ready for the next one
counter--;
} while (counter>0);
lcd_gotoxy(1,1);
printf(lcd_putc," IR Measurement");
lcd_gotoxy(1,2);
printf(lcd_putc,"================");
lcd_gotoxy(1,3);
printf(lcd_putc,"Value =%u",reading);
lcd_gotoxy(1,4);
printf(lcd_putc,"Distance =");
return(reading);
}
void main()
{
lcd_init();
while(true)
{
get_ir_reading();
}
}
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Thanks....Harry |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Oct 20, 2005 7:53 pm |
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The two lines in bold are lines of code, they're not function prototypes.
They call CCS functions. They are not inside main() or any other
function. They cause the following errors when I try to compile the
program:
*** Error 28 Line 10(12,16): Expecting an identifier
*** Error 43 Line 10(17,18): Expecting a declaration
*** Error 28 Line 11(12,16): Expecting an identifier
*** Error 43 Line 11(17,18): Expecting a declaration
| Quote: | #include <16F628.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock=4000000)
#include <LCD_4LINE.c> //this file set up to use port B
#define GP2D02_VIN PIN_B3
#define GP2D02_VOUT PIN_A2
set_tris_a(0xff);
set_tris_b(0x00);
int reading;
int get_ir_reading(); |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Posted: Thu Oct 20, 2005 8:47 pm |
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| Quote: | | When the variable "Reading" goes under a hundred, the value displayed on the LCD goes to three digits. |
You aren't clearing the rest of the line so stale data is on the display. |
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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| Posted: Thu Oct 20, 2005 9:17 pm |
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[quote="Mark"] | Quote: |
You aren't clearing the rest of the line so stale data is on the display. |
Ahhhh....thanks.How can I fix that? If I use a /f then the display flickers. |
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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| Posted: Thu Oct 20, 2005 9:20 pm |
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| PCM programmer wrote: | They cause the following errors when I try to compile the
program:
*** Error 28 Line 10(12,16): Expecting an identifier
*** Error 43 Line 10(17,18): Expecting a declaration
*** Error 28 Line 11(12,16): Expecting an identifier
*** Error 43 Line 11(17,18): Expecting a declaration
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Does that mean that my compiler is not working properly and I should report this to CCS?
Harry |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Posted: Thu Oct 20, 2005 9:39 pm |
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[quote="Harry Mueller"] | Mark wrote: | | Quote: |
You aren't clearing the rest of the line so stale data is on the display. |
Ahhhh....thanks.How can I fix that? If I use a /f then the display flickers. |
One way to to fix the field to a specific length
| Code: | lcd_gotoxy(1,3);
printf(lcd_putc,"Value =%4u",reading);
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Another way is to pad spaces at end
| Code: | lcd_gotoxy(1,3);
printf(lcd_putc,"Value =%u ",reading);
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Another way is to clear the field first
| Code: | lcd_gotoxy(8,3);
printf(lcd_putc," ");
lcd_gotoxy(1,3);
printf(lcd_putc,"Value =%u",reading);
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_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
Last edited by asmallri on Thu Oct 20, 2005 10:50 pm; edited 1 time in total |
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asmallri
Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia
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| Posted: Thu Oct 20, 2005 9:40 pm |
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| Harry Mueller wrote: | | PCM programmer wrote: | They cause the following errors when I try to compile the
program:
*** Error 28 Line 10(12,16): Expecting an identifier
*** Error 43 Line 10(17,18): Expecting a declaration
*** Error 28 Line 11(12,16): Expecting an identifier
*** Error 43 Line 11(17,18): Expecting a declaration
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Does that mean that my compiler is not working properly and I should report this to CCS?
Harry |
If you can really compile the code you posted without errors then it is a bug.
_________________
Regards, Andrew
http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!! |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Oct 20, 2005 10:10 pm |
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You're not using the latest version of the compiler, so reporting a
bug on an older version won't do much good. Also, you're fairly
new. I would hold off on reporting bugs. Rather, look for other causes. |
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Harry Mueller
Joined: 17 Oct 2005
Posts: 116
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| Posted: Fri Oct 21, 2005 8:44 am |
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| PCM programmer wrote: | You're not using the latest version of the compiler, so reporting a
bug on an older version won't do much good. Also, you're fairly
new. I would hold off on reporting bugs. Rather, look for other causes. |
I'm going to pm you on this later.
Asmallri: Thanks a bunch, those suggestion were all better than the solution I came up with.
Cheers....Harry |
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