Rough 'n Ready Audio Frequency extraction with a PIC

[ScaleRobotics]

Well that sure does look clean! For your rough and ready approach, how about a simple count command like this:

COUNT PORTB.1,100,W1

That will count pulses during a 100ms period. Other way to do it for more accuracy is interrupts. But as you say, you just are going to do a lookup table.

Edit:
For the accuracy you need between D and D# etc, you would need to sample for 1 second using this method. If that's too long, you would have to go with interrupts, and measure time between pulses. Another quick and dirty try might be pulsin? Not sure how well that would work on an analog signal though. Maybe you could average a few...

[mark_s]

Here's another approach.
You can use timer 1 as a frequency counter. Not sure if will be accurate enough? You did not say which pic you are using? Timer 1 external input is normally on portc. There should be a way to route the comparator output to tmr1? You will have to play with the pause statement to calibrate the output ie "pause 97" to compensate for the delays in pbp.


CCP1CON = %00000101 ' Capture every rising edge
T1CON = %00000011 ' No prescale/Osc off/Sync on/External source/TMR1 on

Freq var word ' 100ms count result

LOOP:

TMR1H = 0 ' Clear Timer1 high 8-bits
TMR1L = 0 ' Clear Timer1 low 8-bits
T1CON.0 = 1 ' Start 16-bit timer
Pause 100 ' Capture 100 mS of Input
T1CON.0 = 0 ' Stop 16-bit Timer
Freq.BYTE0 = TMR1L ' Read Low 8-bits
Freq.BYTE1 = TMR1H ' Read High 8-bits

GoTo LOOP

[Acetronics2]

Hi, Hank

Tenaja perfectly told what I was thinking to ... except it exists a CMOS version of the 567 ... much less consuming.

now, if you measure a nice filtered sinewave ... without distortion. you must have calculated a very, very, very nice filter ... ( I'm not talking about harmonics, but other very close frequencies that can be mixed with ...).


using the comparator section to create an interrupt , or better the CCP capture feature ... will give you the info with less than a cycle delay ...

You call that " fun " ... small gambler you are !!!

Alain

[HankMcSpank]

Guys...thanks for your input - I'll take time later to consider them all in detail.

In the meantime, a bit more info.

I need to capture the frequency soon after the string is plucked but not too soon else too many complex harmonics are still embedded in the signal. I'd imagine coming in to make my 'sample' about 300ms after the pluck (I have a preset PIC threshold that when breached assumes a note has been plucked, which will allow me to pause 300ms before sampling).

I can't imagine going past 500ms after the note has been plucked (else the note will have decayed too much) so this only gives a maximum window of about 200ms to glean what the frequency is.

If it helps, I'm using a 16F690.

Acetronics - just seen your post - I'm using a sustainer which thankfully drops out all harmonics and leaves a relatively pure fundamental ( http://www.youtube.com/user/hankmcsp.../0/u6gm5fY1wM0 ie a nice sinewave!) Wrt to sustain - some frquencies are quite tricky to sustain, so I need to know when they're plucked to trigger special handling

[HankMcSpank]

Got to laugh - 16f690 ...absolute mare for a noobesque personage like meself..

I wouldn't mind but I've tackled so much with that PIC variant...but comparators? WTF?! The datasheet has ma heed buzzin.

I've decided a nice easy entry into the world of comparators is now going to be with a simpler 12F683. Once I nail the concepts with that, then I shall take a few swigs of stiff whisky & get out the 16F690 datasheet again - were microchip having a laugh with that on?

[Darrel Taylor]

I've thought about doing something like that too,

And I think without external hardware and using the comparator, the DFT idea Josuetas was working with a while back might have the best chance at detecting the notes.
It may even be able to detect multiple notes at the same time (chords).

I played with the spreadsheet, but didn't try any hardware.

And whether the resolution will be tight enough to distinguish 9/8, 10/9 and 16/15ths steps, I don't know either.
It was originally for DTMF tones.

Might be worth a look though.
http://www.picbasic.co.uk/forum/show...2606#post42606

And the original AppNote (AN257) ...
http://www.microchip.com/stellent/id...pnote=en024294

<br>

[HankMcSpank]

Thanks Darrel....I'll check it out later.

So here's the ludicrously simple 'get me up & running' setup I have (lifted/edited fromthe Microchip Tips' n trick sheet)



I put a sawtooth from a sig gen on the comparator input, but get nowt on the output

Now like I say, I always struggle with the registers - and even then, it's been a while - so try not to laugh...

@MyConfig = _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON  
@MyConfig = MyConfig & _MCLRE_OFF 

DEFINE OSC 4           ' Internal 4MHz

CMCON0 = %00000001   	'CIN pins are configured as analog, COUT pin configured as Comparator output?
ADCON0 = %00000000	'ADC disabled?
ANSEL = %00001111	'All Analogue inputs enabled?
TRISIO = %111011	'GPIO2 output (Comparator Out)

' PIN# NAME     USE & CONNECTION
'  1   Vdd      +5VDC power supply
'  2   GPIO.5   Debug Port (PicKit2 needs switching from here to pin Pin 7 to allow programming)
'  3   GPIO.4   
'  4   GPIO.3   
'  5   GPIO.2   Comparator Out (GP2)
'  6   GPIO.1   CIN-  Signal In  (GP1)
'  7   GPIO.0   CIN+  trigger level (GP0)
'  8   Vss      Power supply ground
'-------------------------------------------------------------------------

EDIT Ok, spotted it..

ANSEL = %00001011		'All Analogue inputs except AN2 enabled

& here we have an output...



Now...what to do with the output?!!!

[Byte_Butcher]

Now...what to do with the output?!!!

On the rising edge of your square wave, start a timer running. When the next rising edge comes along, grab the timer count so you can calculate the period of the square wave, and reset the timer for the next go around.

If your waveform is symmetrical you could start the timer on the rising edge and stop on the falling edge and get your frequency in 1/2 cycle.
Maybe...


steve