Overview
The oscilloscope firmware provides real-time analog-to-digital conversion (ADC) streaming from two input channels. It runs on ESP32 and can stream ADC data over serial at configurable sample rates.
Pin Configuration
#define ADC1_PIN 34 // ADC Channel 1 (GPIO 34)
#define ADC2_PIN 35 // ADC Channel 2 (GPIO 35)
GPIO 34 and 35 are ADC1 channels on ESP32 and are input-only pins, making them ideal for analog measurements.
Sampling Configuration
#define ADC_READ_INTERVAL_US (1000000 / 200) // 200 samples per second
volatile bool adcStreaming = false; // Streaming flag
unsigned long lastAdcMicros = 0; // Last sample timestamp
Sample Rate Calculation
The sample interval is calculated as:
Interval (μs) = 1,000,000 / Sample Rate (Hz)
1,000,000 / 200 = 5,000 μs (5 ms between samples)
Command Protocol
Starting ADC Streaming
Send the following command over serial:
Response:
Stopping ADC Streaming
Response:
When streaming is active, data is sent in CSV format:
S,<adc1_value>,<adc2_value>
Example Output
S,2048,1856
S,2050,1860
S,2045,1855
S,2052,1862
- Prefix:
S, indicates a sample line
- ADC1: First value (0-4095)
- ADC2: Second value (0-4095)
ESP32 ADC has 12-bit resolution, providing values from 0 to 4095 (0V to 3.3V).
Setup Function
void setup() {
Serial.begin(115200);
delay(1000);
// ADC pins are input-only by default
// No pinMode() configuration needed for GPIO 34, 35
Serial.println("Generador listo - CH1 y CH2 totalmente independientes");
}
Main Loop - ADC Streaming
void loop() {
// Process serial commands
if (Serial.available()) {
String cmd = Serial.readStringUntil('\n');
cmd.trim();
if (cmd.length() == 0) return;
if (cmd == "ADC START") {
adcStreaming = true;
Serial.println("ADC STREAMING STARTED");
}
else if (cmd == "ADC STOP") {
adcStreaming = false;
Serial.println("ADC STREAMING STOPPED");
}
}
// Stream ADC data at specified interval
if (adcStreaming) {
unsigned long now = micros();
if (now - lastAdcMicros >= ADC_READ_INTERVAL_US) {
lastAdcMicros = now;
int adc1 = analogRead(ADC1_PIN);
int adc2 = analogRead(ADC2_PIN);
Serial.print("S,");
Serial.print(adc1);
Serial.print(",");
Serial.println(adc2);
}
}
}
ADC Reading Function
The ESP32 analogRead() function:
int adc1 = analogRead(ADC1_PIN); // Returns 0-4095
int adc2 = analogRead(ADC2_PIN); // Returns 0-4095
Voltage Conversion
To convert ADC values to voltage:
float voltage1 = (adc1 / 4095.0) * 3.3; // 0V to 3.3V
float voltage2 = (adc2 / 4095.0) * 3.3; // 0V to 3.3V
Timing Precision
The firmware uses micros() for microsecond-level timing:
unsigned long now = micros();
if (now - lastAdcMicros >= ADC_READ_INTERVAL_US) {
lastAdcMicros = now;
// Perform ADC reading
}
Sample Rate Configuration
To modify the sample rate, change the definition:
// 100 Hz (10ms interval)
#define ADC_READ_INTERVAL_US (1000000 / 100)
// 500 Hz (2ms interval)
#define ADC_READ_INTERVAL_US (1000000 / 500)
// 1000 Hz (1ms interval)
#define ADC_READ_INTERVAL_US (1000000 / 1000)
Higher sample rates require faster serial baud rates. At 115200 baud, effective maximum sample rate is approximately 1000 Hz for two channels.
Integration with Signal Generator
The oscilloscope firmware is integrated with the signal generator in the same sketch:
// Combined firmware supports:
// - ADC streaming (oscilloscope)
// - DAC output (signal generator)
// Both functions operate independently
Command Processing Flow
if (Serial.available()) {
String cmd = Serial.readStringUntil('\n');
cmd.trim();
if (cmd == "ADC START") {
adcStreaming = true;
}
else if (cmd == "ADC STOP") {
adcStreaming = false;
}
else {
// Process signal generator commands
processCommand(cmd);
}
}
Key Features
- Dual-channel ADC with simultaneous sampling
- Configurable sample rate via
ADC_READ_INTERVAL_US
- CSV data format for easy parsing
- Microsecond timing for precise intervals
- Serial command control for start/stop
- 12-bit resolution (0-4095 range)
- Non-blocking operation in main loop
ESP32 ADC Specifications
| Parameter | Value |
|---|
| Resolution | 12-bit (0-4095) |
| Input Range | 0V to 3.3V |
| ADC Channels | ADC1: GPIO 32-39
ADC2: GPIO 0, 2, 4, 12-15, 25-27 |
| Recommended Pins | GPIO 34, 35 (input-only, no pull-up/down) |
| Max Sample Rate | ~40 kHz (hardware limit) |
ADC2 is used by WiFi. For reliable ADC readings, use ADC1 channels (GPIO 32-39) when WiFi is active.