Frequency detection (audio)

[Ramius]

Hi Hank,
This may sound like a dumb question and you are doing an analog to digital conversion at some point? Also if you only wish to work with half wave, a simple diode will do this for you. Best, Ed

[HankMcSpank]

Firstly, I spoke to soon. Whilst this latest method mentioned in my last post has allowed me to detect higher frequencies....I'm still getting erratic results in & around the 450-700Hz audio frequency range!

Ramius - re Ato D'ng....no this is purely to detect frequency (although I do intend using the pic's AtoD as an envelope detect to actually trigger the frequency detection).

[HankMcSpank]

Ok, it looks like interrupts are a big no-no here so I've established a way of doing this without an interrupt...

T1GCON.4 = 1
Loop1:
pause 500
T1GCON.3 = 1
TMR1=0
while  T1GCON.3 = 1
wend
count1=tmr1
HSEROUT [dec count1,13,10]
GOTO Loop1

The above can detect up to 50khz audio input (can probably go higher...but the amount of timer1 counts between comparator edges gets less, so the 'percentage error' increases)

Basically I'm using a Timer gate single pulse mode (T1GCON.4 = 1), then forcing the other part of the single pulse mechanism to a 1 ( Single-Pulse Acquisition Status bit T1GCON.3 = 1), after the comparator2 output drops then T1GCON.3 is dropped to a zero automatically, I therefore use a wend to loop until T1GCON.3 = 1 is a 0 ....then I ouput the timer1 counts. My only problem is I'm getting a zero reading intermittently, but other than that, the counts are pretty solid.

here's the TMR counts for 1,000Hz....

1824
1824
1825
1825
1826
0
1824

just got to get to the bottom of why those readings of 0 are creeping in .....

[Ramius]

Hi Hank,
The only thing I can think of is the method you are using to couple the audio signal you wish to measure. Hopefully you are using a capacitor? To chose the best value would be with the formula Xc= .159/F*C "F" is in hertz "C" is in farads and in most audio work .047 mfd is common. Xc give the "resistive" value for a capacitor to AC. Again I am not sure how you would ever obtain great accuracy without conversion to a square wave with a consistant time duration. Again hope this helps. Best, Ed