As filter I used a Bandpassfilter where a frequency of 220Hz should pass. I set the lower cut off frequency at 215Hz and the upper cut off frequency at 225Hz (more details in the posted sketchs).
The good news is that the sketch works, but instead that pass my desired frequency of 220Hz, passes a frequency of 275Hz.
To exclude errors I did also tests with my Filter-LED sketch:
// Arduino Signal Filtering Test
// Turn a LED on if filter amplitude reaches an arbitrary threshold.
// 2014
// Arduino Signal Filtering Library
// Copyright 2012-2013 Jeroen Doggen (jeroendoggen@gmail.com)
//http://jeroendoggen.github.io/Arduino-signal-filtering-library/
//http://www.schwietering.com/jayduino/filtuino/
#include <SignalFilter.h> // Filter Library
SignalFilter Filter;
const int ledPin = 13; // pin that the LED is attached to
const int threshold = 512; // an arbitrary threshold level that's in the range of the analog input
/* // Variable for time measurement
unsigned long time_start; // variable for time measurement start
unsigned long time_sampl; // variable for time measurement sample
int incomingByte = 0; // sets incoming Byte to 0
*/
int data1; // variable for Analog In
int data2; // variable for filter
void setup()
{
pinMode(ledPin, OUTPUT); // initialize the LED pin as an output:
// Serial.begin(9600); // used only printing (debugging)
Filter.begin();
Filter.setFilter('c'); // filter settings: c=Cebycheff b= Bessel
Filter.setOrder(2); // filter settings: order 1 or 2
}
/*
Filter characteristics are stored in: “SignalFilter.cpp”.
Current filter settings and code: for “c” “2”
/// runChebyshev: Band Pass 220Hz; 1. Order; lower corner =215Hz; upper corner 225Hz; sampling=5000Hz; long type 8bit; enabled "-1 bit saturation";
_v[0] = _v[1];
_v[1] = _v[2];
long tmp = ((((data * 3360365L) >> 8) //= ( 6.2591678898e-3 * x)
+ ((_v[0] * -4141801L) >> 1) //+( -0.9874824279*v[0])
+ (_v[1] * 4009861L) //+( 1.9120508347*v[1])
)+1048576) >> 21; // round and downshift fixed point /2097152
_v[2]= (short)tmp;
return (short)((
(_v[2] - _v[0]))); // 2^
*/
void loop()
{
// Read Analog Input... you can connect accelerometer, gyro, temperature sensor, microphone etc to the channel
data1 = analogRead(0)-512; //Read Analog channel (value of microphone) and substract DC-Offset from Microphone "BOB-09964"
data2 = Filter.run(data1); //Read the filtered signal
/*
http://arduino.cc/en/Tutorial/IfStatement
the variable called data1 is used to store the data collected from a Analog Pin A0.
This data is then compared to a threshold value.
If the the value is found to be above the set threshold the LED connected to digital pin 13 is turned on.
If analogValue is found to be < threshold, the LED remains off. */
// if the filter value is high enough, turn on the LED:
if (data2 > threshold) {
digitalWrite(ledPin, HIGH);
}
else {
digitalWrite(ledPin,LOW);
}
/* // time measurement for debugging:
time_start = micros(); //time measurement
data1 = analogRead(0); // for Analog Pin A0
data2 = Filter.run(data1); // for filter calculation
time_sampl = micros() - time_start; //time measurement math
if (Serial.available() > 0) {
incomingByte = Serial.read();
if (incomingByte == 'm') { // enter and sent "m" in serial monitor window and read time in microsec for Filter.run(data1) and analog read
Serial.print("Time Sample = ");
Serial.println(time_sampl, DEC);
}
} */
}
But also there nearly the same problem: 220Hz doesn’t pass but a frequency of 306Hz?! :~
Do you understand this bug? Are there maybe more variables from filter depends?