From a539257a3829c699092ca1e048a1657a36c357be Mon Sep 17 00:00:00 2001
From: lbernstone <lbernstone@gmail.com>
Date: Thu, 10 Jan 2019 00:24:17 -0700
Subject: [PATCH] An example to read high frequency analog data using i2s_adc
 (#2295)

---
 .../examples/I2S/HiFreq_ADC/HiFreq_ADC.ino    | 71 +++++++++++++++++++
 1 file changed, 71 insertions(+)
 create mode 100644 libraries/ESP32/examples/I2S/HiFreq_ADC/HiFreq_ADC.ino

diff --git a/libraries/ESP32/examples/I2S/HiFreq_ADC/HiFreq_ADC.ino b/libraries/ESP32/examples/I2S/HiFreq_ADC/HiFreq_ADC.ino
new file mode 100644
index 00000000000..83538db59bb
--- /dev/null
+++ b/libraries/ESP32/examples/I2S/HiFreq_ADC/HiFreq_ADC.ino
@@ -0,0 +1,71 @@
+/*
+ * This is an example to read analog data at high frequency using the I2S peripheral
+ * Run a wire between pins 27 & 32
+ * The readings from the device will be 12bit (0-4096)
+ */
+#include <driver/i2s.h>
+
+#define I2S_SAMPLE_RATE 78125
+#define ADC_INPUT ADC1_CHANNEL_4 //pin 32
+#define OUTPUT_PIN 27
+#define OUTPUT_VALUE 3800
+#define READ_DELAY 10000 //microseconds
+
+void i2sInit()
+{
+   i2s_config_t i2s_config = {
+    .mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_ADC_BUILT_IN),
+    .sample_rate =  I2S_SAMPLE_RATE,              // The format of the signal using ADC_BUILT_IN
+    .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT, // is fixed at 12bit, stereo, MSB
+    .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
+    .communication_format = I2S_COMM_FORMAT_I2S_MSB,
+    .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,
+    .dma_buf_count = 4,
+    .dma_buf_len = 8,
+    .use_apll = false,
+    .tx_desc_auto_clear = false,
+    .fixed_mclk = 0
+   };
+   i2s_driver_install(I2S_NUM_0, &i2s_config, 0, NULL);
+   i2s_set_adc_mode(ADC_UNIT_1, ADC_INPUT);
+   i2s_adc_enable(I2S_NUM_0);
+}
+
+void reader(void *pvParameters) {
+  uint32_t read_counter = 0;
+  uint64_t read_sum = 0;
+  while(1){
+    size_t bytes_read = 0;
+    uint16_t buffer = 0;
+    i2s_read(I2S_NUM_0, &buffer, sizeof(buffer), &bytes_read, portMAX_DELAY);
+    buffer = ~buffer;            // The data is inverted
+    //Serial.println(buffer % 0x1000);
+    read_sum += buffer % 0x1000; // The 4 high bits are the channel
+    read_counter++;
+    if (bytes_read != sizeof(buffer)) Serial.println("buffer empty!");
+    if (read_counter == I2S_SAMPLE_RATE) {
+      Serial.printf("avg: %d\n", read_sum/I2S_SAMPLE_RATE);
+      read_counter = 0;
+      read_sum = 0;
+      i2s_adc_disable(I2S_NUM_0);
+      delay(READ_DELAY);
+      i2s_adc_enable(I2S_NUM_0);
+
+    }
+  }
+}
+
+void setup() {
+  Serial.begin(115200);
+  // Put a signal out on pin 
+  uint32_t freq = ledcSetup(0, I2S_SAMPLE_RATE, 10);
+  Serial.printf("Output frequency: %d\n", freq);
+  ledcWrite(0, OUTPUT_VALUE/4);
+  ledcAttachPin(OUTPUT_PIN, 0);
+  // Initialize the I2S peripheral
+  i2sInit();
+  // Create a task that will read the data
+  xTaskCreatePinnedToCore(reader, "ADC_reader", 2048, NULL, 1, NULL, 1);
+}
+
+void loop() {}