Help with car speedo meter

[Guest]

Hi iam trying to make speedometer for my car
i get speed pulse from the car and then transform it to pic then lcd
i used the Ex_freqc and modified it to show the pulse on the lcd
i had measure the frequency with my fluke and i've got readings from the speed pulse like when iam at 30 km/h i got 5000 hz
so i will do some math to transform it from Hz to Km/h the weird thing that i put the lcd_init(); in the loop and the lcd was blinking and test it in vechile the counter started to go up and down according to the speed i was pleased that i got some results but as known i was putting 12V to the pin of the PIC the C0 and C1 pins gone, so i put resistor and zener to protect the pin and got no result from the car rarely i was got 1 or 3 pulses
here is my code

[Guest]

anybody can Help me !

[PCM programmer]

The reason no one wants to help is because the code in your post
is very poorly formatted.

1. The comments are too long and they wrap around to the next line.

2. You have several C statements on the same line.

3. You have some kind of ASCII art in there, and it's all messed up.

The code is basically unreadable.

You need to carefully re-format your code, and use the PREVIEW
button to check it, before you post it. Also, after you post, look
at the code and if the formatting is still bad, then EDIT the post
and fix it. Then people will likely help.

[necati]

#include <16F877A.h>
#fuses HS,NOWDT,NOLVP
#use delay(clock=20000000) //one instruction=0.2us
#bit t1_overflow = 0x0C.0 // Input pin c1
#include "LCD.c"
#define use_portb_lcd
void main() {
int cycles8, cycles;
int32 freq ;
long freqc_high;
long freqc_low;
lcd_init();
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
}
delay_cycles(216); //y
cycles++; ///1 cycle
}
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
freq=freq/(500/3);//****************************************
printf(lcd_putc,"\f %LU kmh ",freq); //and print frequency //Here You put your formula of speed

}}

[info@ckmintech.com]

Recently we have built a very similar device for our client (the speed and mileage data is sent to a PC). I cannot give you the source code, however you should consider the following desgin hints.

1. K-value ( how many pulses you will receive for travelling 1 km)

2. connect the pulse output of the car to a 78L05 input and 78L05 output to a chip pin which has interrupt-on-change feature. The input and ouput of 78L05 should have a 0.1u cap to the ground.

3. Setup port-change-interrupt to count how many pulse received
4. setup RTCC interrupt to count number of pulse received in a fixed period, using simple calculation you can get the speed.

[PCM programmer]

[Guest]

i heard that measuring pulses by frequency
is faster than interrupt (faster update) is that right ?

and what about the interference in the car to pic ?

info@ckmintech.com : How to get the K-value

Thanks

[sjbaxter]

[Ttelmah]

I think you are slightly misunderstanding.
If you are measuring the frequency of pulses (which is what you are doing), there are two seperate choices. the first is to measure the interval _between_ pulses, by counting some higher frequency in this interval. The second is to count the source pulses over some longer interval of time. It is the former that is the faster updating solution.
The best way of doing this, is to count how many pulses of your master PIC crystal, occur between successive edges of the incoming pulse.
The 'k' factor in the equation given depends on the diameter of the wheels of the car, where the sensor is 'relative' to these (any gearing between), and how many pulses per revolution occur (it is common to have multiple magnets on the shaft, both to maintain balance, and to increase the number of pulses available).
As an example, if you have a PIC running at 4MHz, and a magnet on the output shaft to a wheel, with no gearing between, and 2 pulses/rev, then for a car with 15" wheels, and tires 6.2" high (225*70), the outside diameter will be 27.4", with the circumference 86.08". You will then get 1472.04 pulses/mile (((1760*36)/86.08)*2). At 10mph, you will get about 4 pulses/second ((1472.04*10)/(60*60)). If you count pulses per second, then the update rate becomes one/second, and the speed would need to increase to 12.2mph, before you reliably get an extra pulse per second (if you only have one pulse per rev, this doubles. If instead you count the pulses of the master clock/4 (available using the internal timer on most PICs), then at 10mph, the interval is 244558 clocks, and you can detect changes of tiny fractions of a mph, and update whenever a pulse arrives.

Best Wishes

[info@ckmintech.com]

You can ask the k-value from your odometer supply. Our designe is using on 2 Toyota van, their k-value are 2454 and 2360. May be you can use this value to start your project as a reference and do the calibration later.

Refer to counting pules by using port-interrupt. Our design is using 18F1220 running on 8MHz and did not have any problem.

Rgd.