Session 1
- Time
- 2025-11-01 15:30
- People
- Sun, Eitan, Ben, Edward, Charlie, Ceci, Abby, Matti, Ruipeng, Saetbyeol
Speaker Spec
- 8 ohm, 0.5 watt
Process
- Sun prepared a speaker playing sine tone at different frequencies and amplitudes
- Ben explained how we "average" the DC voltage using V_msr
- Ceci performed in-series current measurements, in-parallel voltage measurements, and Sun recorded the data
| Amplitude | I (amp) | V (v) | Power (w) |
|---|---|---|---|
| 4000 | 0.020 | 0.195 | 0.0039 |
| 8000 | 0.045 | 0.380 | 0.0171 |
| 16000 | 0.095 | 0.770 | 0.07315 |
| 32000 | 0.185 | 1.555 | 0.2877 |
Observation
- Both voltage and current are proportional to amplitude
- Hence, power is proportional to the square of amplitude
Appendix
Test code
#include "AudioTools.h"
/**
* Pinout:
* D0 - I2S BCLK
* D2 - I2S LRC
* D10 - I2S DIN (to speaker)
*/
#define I2S_BCLK D0
#define I2S_LRC D2
#define I2S_DIN D10
const int freqs[] = {220, 440, 660, 880};
const int amps[] = {4000, 8000, 16000, 32000};
int freqIndex = 0;
int ampIndex = 0;
unsigned long lastChange = 0;
const int sampleRate = 22000; // sample rate in Hz
AudioInfo info(sampleRate, 1, 16);
SineWaveGenerator<int16_t> sineWave(32000); // sine wave with max amplitude of 4000
GeneratedSoundStream<int16_t> sound(sineWave); // stream generated from sine wave
I2SStream out;
StreamCopy copier(out, sound); // copies sound into i2s
void setup() {
Serial.begin(115200);
Serial.println("I2S Sine Wave Playback");
AudioToolsLogger.begin(Serial, AudioToolsLogLevel::Warning);
// start I2S with custom pinout
Serial.println("Starting I2S...");
auto config = out.defaultConfig(TX_MODE);
config.copyFrom(info);
config.pin_bck = I2S_BCLK;
config.pin_ws = I2S_LRC;
config.pin_data = I2S_DIN;
out.begin(config);
// Setup sine wave
sineWave.begin(info, freqs[0]);
Serial.println("Started sine wave playback");
}
void loop() {
if (millis() - lastChange >= 2000) {
lastChange = millis();
freqIndex = (freqIndex + 1) % 4;
if (freqIndex == 0) {
ampIndex = (ampIndex + 1) % 4;
}
sineWave.setFrequency(freqs[freqIndex]);
sineWave.setAmplitude(amps[ampIndex]);
}
copier.copy();
}