diff options
| -rw-r--r-- | examples/test-session.cpp | 17 |
1 files changed, 9 insertions, 8 deletions
diff --git a/examples/test-session.cpp b/examples/test-session.cpp index 1a53c66..97d5754 100644 --- a/examples/test-session.cpp +++ b/examples/test-session.cpp @@ -759,7 +759,8 @@ void cmd_board_info(void) { // TODO print more information // -- Helper functions -------------------------------------------------------- void measure_adc_noise(uint8 pin) { - uint16 data[100]; + const int N = 1000; + uint16 x; float mean = 0; float delta = 0; float M2 = 0; @@ -767,21 +768,21 @@ void measure_adc_noise(uint8 pin) { // Variance algorithm from Welford, via Knuth, by way of Wikipedia: // http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#On-line_algorithm - for (int i = 0; i < 100; i++) { - data[i] = analogRead(pin); - delta = data[i] - mean; - mean = mean + delta / (i + 1); - M2 = M2 + delta * (data[i] - mean); + for (int i = 1; i <= N; i++) { + x = analogRead(pin); + delta = x - mean; + mean += delta / i; + M2 = M2 + delta * (x - mean); } SerialUSB.print("header: D"); SerialUSB.print(pin, DEC); SerialUSB.print("\tn: "); - SerialUSB.print(100, DEC); + SerialUSB.print(N, DEC); SerialUSB.print("\tmean: "); SerialUSB.print(mean); SerialUSB.print("\tvariance: "); - SerialUSB.println(M2 / 99.0); + SerialUSB.println(M2 / (float)(N-1)); pinMode(pin, OUTPUT); } |