 |
 |
| View previous topic :: View next topic |
| Author |
Message |
ruud
Joined: 10 Sep 2007
Posts: 2
|
| Analog Input 16F877 |
 Posted: Mon Sep 10, 2007 4:09 am |
 |
|
We like to use a 16F877 to detect the frequenty of an inductive sensor.
Later we have to translate it to rpm's (combustionmotor)
We like to us an ananog input ofthis chip and a comparator (in or extern). The max frequeny we like to detect is 25 Khz.
annyone suggestions or example code! : 
Thanks Ruud.
University of technology Eindhoven. |
|
 |
Humberto
Joined: 08 Sep 2003
Posts: 1215
Location: Buenos Aires, La Reina del Plata
|
|
| Posted: Mon Sep 10, 2007 5:04 am |
|
|
| Quote: |
annyone suggestions or example code!
|
EX_FREQC.C (Examples folder of your Compiler packet) will show you the way to start with.
There are no reason to use an analog input to measure or counting pulses, because
the variable magnitude of an inductive sensor is the period, not the amplitude.
Humberto |
|
|
ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
|
|
| Posted: Mon Sep 10, 2007 6:27 am |
|
|
The 16F877 is an old chip model, not recommended for new designs. Consider using a newer chip like the PIC16F887.
25kHz is at the top end of the PIC16 capabilities, depending on the input signal you might not be able to get up to this speed. You might consider using a PIC18 chip, some of the newer models have a sampling speed of up to 200kHz. |
|
|
ruud
Joined: 10 Sep 2007
Posts: 2
|
|
| Posted: Wed Sep 19, 2007 8:56 am |
|
|
| Humberto wrote: | | Quote: |
annyone suggestions or example code!
|
EX_FREQC.C (Examples folder of your Compiler packet) will show you the way to start with.
There are no reason to use an analog input to measure or counting pulses, because
the variable magnitude of an inductive sensor is the period, not the amplitude.
Humberto |
I tried this example. It has to count the zero crossings of a signal fot 1 second. (zero crossings doesnt work, It counts only pulses above 4 V).
Anyone an idea whats wrong.
This is the example code:
/////////////////////////////////////////////////////////////////////////
//// EX_FREQC.C ////
//// Counts the 'zero' crossings of an input signal for 1 second, ////
//// therefore counting the frequency of the signal. The input ////
//// signal's frequency is then displayed over the serial port. ////
//// ////
//// The 1s delay is created by generating a perfect 5,000,000 ////
//// cycles (it takes 0.2us for one cycle at 20Mhz). The trick is ////
//// that conditional statements have different values of cycles ////
//// depending on a TRUE or FALSE jump. ////
//// ////
//// The input signal is to be supplied to PIN C0 ////
//// ////
//// This example will work with thePCM compiler. The ////
//// following conditional compilation lines are used to include a ////
//// valid device for each compiler. Change the device and clock ////
//// for your hardware if needed. ////
/////////////////////////////////////////////////////////////////////////
//// (C) Copyright 1996,2003 Custom Computer Services ////
//// This source code may only be used by licensed users of the CCS ////
//// C compiler. This source code may only be distributed to other ////
//// licensed users of the CCS C compiler. No other use, ////
//// reproduction or distribution is permitted without written ////
//// permission. Derivative programs created using this software ////
//// in object code form are not restricted in any way. ////
/////////////////////////////////////////////////////////////////////////
#include <16F877.h>
#fuses HS,NOWDT,NOLVP
#use delay(clock=20000000) //one instruction=0.2us
#use rs232(baud=9600, xmit=PIN_c6, rcv=PIN_c7)
#bit t1_overflow=0x0C.0
// #bit t1_overflow=0xF9E.0 (PIC18, Reminder)
void main() {
int cycles8, cycles;
int32 freq;
long freqc_high;
long freqc_low;
while (TRUE) {
cycles8=0;
cycles=0;
freqc_high=0;
t1_overflow=0;
set_timer1(0);
setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1);
/* ___ wait one second ___ */
while (cycles!=0xFF) { //true=3, false=4
cycles8=0; //1 cycle
//start inner loop
while (cycles8!=0xFF) { //true=3, false=4
if (t1_overflow)//true=2,false=3 //----|
{t1_overflow=0;freqc_high++;}//6 cycles // |
else // |-- 8 cycles
{delay_cycles(5);} //----|
delay_cycles(62); //x
cycles8++; //1
///2 cycles to jump to top
//math: end inner loop
//math: total inner loop=((3+8+x+1+2)*255 + 4)*255
//math: if x=62.87781 then inner loops takes 5mil instructions
//math: if x=62 then inner loop takes 4942920, have to fill 57080 cycles
}
delay_cycles(216); //y
cycles++; ///1 cycle
///2 cylces to jump to top
//math: outer=(3+1+y+1+2)*255+4=57080
//math: y=(57080-4)/255)-(3+1+0+0+1+2)
//math: if y=216.827450980392156862745098039216 then outer loop cylces is 57080
//math: if y=216 then outer loop cycles is off by 211 cycles. z=211
}
delay_cycles(211); //z
/* ___ end waiting 1 second ___ */
setup_timer_1(T1_DISABLED); //turn of counter to prevent corruption while grabbing value
if (t1_overflow) //check one last time for overflow
freqc_high++;
freqc_low=get_timer1(); //get timer1 value as the least sign. 16bits of freq counter
freq=make32(freqc_high,freqc_low); //use new make32 function to join lsb and msb
printf("%LU Hz\r\n",freq); //and print frequency
}
} |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
