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Maheshi
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| transmitting a step sine wave using PIC |
 Posted: Tue Mar 03, 2009 8:24 pm |
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I need to transmit a step sinewave so that it can be viewed in the oscilloscope using PIC18F46K20. However I do not know how to transmit a signal to the oscilloscope. I'm using MPLAB.
Can anybody suggest the code to do this.
Thanks
Maheshi |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Mar 03, 2009 8:28 pm |
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See this CCS example file:
| Quote: | | c:\Program Files\picc\Examples\Ex_Sine.c |
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Maheshi
Guest
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| transmitting a step sine wave to the oscilloscope |
| Posted: Wed Mar 04, 2009 7:37 pm |
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| I'm sorry but how do I access the file. I am new to this site. |
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SherpaDoug
Joined: 07 Sep 2003
Posts: 1640
Location: Cape Cod Mass USA
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| Posted: Wed Mar 04, 2009 8:42 pm |
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If you have the CCS compiler installed on your PC you should have a directory on your hard disk called picc\Examples. That directory should have a file called Ex_Sine.c.
I question if you are expecting to get an analog signal from your PIC? The PIC is inherently a digital device. The closest it comes to an analog output is PWM, but that is still a square wave until it is put through a low pas filter. You could drive a D/A chip from the PIC and use your scope to look at the analog output of the D/A chip. I don't know of any PICs with built in D/A.
_________________
The search for better is endless. Instead simply find very good and get the job done. |
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dbotkin
Joined: 08 Sep 2003
Posts: 197
Location: Omaha NE USA
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| Posted: Thu Mar 05, 2009 8:47 am |
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Maheshi,
Here is how I did it using PWM. This isn't the complete program - you really don't want to go through a few thousand lines of code -- but hopefully this will help you get on the right track.
| Code: |
const long int s_table[] = {128,176,218,246,255,246,218,176,
128,79,37,9,0,9,37,79};
// This function steps the PWM duty cycle value when Timer0 overflows.
#int_rtcc
void pwm_tone(void) {
set_pwm1_duty(s_table[s_table_idx++ % 16]);
set_timer0(t0preload);
}
void main() {
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_8|RTCC_8_BIT);
setup_timer_2(T2_DIV_BY_1,63,1);
setup_ccp1(CCP_PWM);
set_pwm1_duty(0);
...
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How does it work? TIMER0 interrupts on a regular basis depending on your clock frequency. Every time it does, the PWM duty cycle is set from the s_table values. I derived those using Excel -- what is shown here gave me a very nice looking sine wave with just a little ripple. I have since switched to a table with only 8 values, which saves CPU time at the expense of a little less smooth waveform.
The t0preload value is used to determine the audio frequency of the resulting sine wave. Again, the values to use depend entirely on your PIC's clock speed. For example, I'm using a PIC18F4620 running at 32 MHz. Preloading Timer0 with a value of 18 will give a 500 Hz wave.
The output of the PWM is low-pass filtered using a series 5K Ohm resistor and a .1 uF capacitor to ground. The filter component values may need to be adjusted depending on your choice of frequencies. Generally, the higher your PWM frequency is the better off you'll be.
Of course after typing all of that I remembered this, complete with a picture of what I ended up with:
http://www.ccsinfo.com/forum/viewtopic.php?t=36540 |
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Maheshi
Guest
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| sine wave |
| Posted: Tue Mar 10, 2009 10:30 am |
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| Thanks a lot Dbotkin . Is it possible for you to post ur entire main program. Im still trying to output the sine wave so I can start working with it to modulate and demodulate signals. |
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