> ## Documentation Index
> Fetch the complete documentation index at: https://learn.pcbcupid.com/llms.txt
> Use this file to discover all available pages before exploring further.

> Wire a light-dependent resistor (LDR) to the Glyph ESP32-C6 board and read analog values to measure ambient light levels in your IoT projects.

# LDR Light Sensor

# Interfacing an LDR with GLYPH board

An LDR (Light Dependent Resistor), also known as a photoresistor, is a variable resistor that changes its resistance based on the intensity of light falling on it.

**How an LDR Works**:
Light Intensity vs. Resistance:
In darkness, the resistance of an LDR is very high (in the range of megaohms, MΩ).
In bright light, the resistance drops significantly (to a few hundred ohms, Ω).

**Material Composition**:
LDRs are made of semiconductor materials like cadmium sulfide (CdS), which have high resistance in darkness but become more conductive when exposed to light (due to photon energy freeing electrons).

**LDR in a Circuit**:
Voltage Divider Circuit:
An LDR is often used in a voltage divider with a fixed resistor to convert changes in light intensity into voltage variations.
The voltage across the LDR can be measured using a microcontroller (e.g., ESP32, Arduino).

**Controlling Devices**:
LDRs are used in automatic streetlights, light meters, and solar tracking systems to control relays, LEDs, or other devices based on ambient light levels.

## Step 1: Hardware Required

1. GLYPH Board
2. Light Dependent Resistor (LDR)

## Step 2: Circuit Diagram

<div style={{ textAlign: "center" }}>
  <img src="https://files.pcbcupid.com/Documentation/Boards/Examples/ldr/idr_circuit%20diagram/ldr_glyph.jpg" alt="pcbcupid-ldr-circuit" width="600" />
</div>

<br />

## Step 3: Code Setup

```cpp theme={null}
#define LIGHT_SENSOR_PIN 3 // GLYPH-C6 pin GPIO 3 (ADC channel)

void setup() 
{
  // initialize serial communication at 115200 bits per second:
  Serial.begin(115200);

  // set the ADC attenuation to 11 dB (up to ~3.3V input)
  analogSetAttenuation(ADC_11db);
}

void loop() 
{
  // reads the input on analog pin (value between 0 and 4095)
  int analogValue = analogRead(LIGHT_SENSOR_PIN);

  Serial.print("Analog Value = ");
  Serial.print(analogValue);   // the raw analog reading

  // We'll have a few thresholds, qualitatively determined
  if (analogValue < 40) 
  {
    Serial.println(" => Dark");
  } 
  else if (analogValue < 800) 
  {
    Serial.println(" => Dim");
  } 
  else if (analogValue < 2000) 
  {
    Serial.println(" => Light");
  } 
  else if (analogValue < 3200) 
  {
    Serial.println(" => Bright");
  } 
  else 
  {
    Serial.println(" => Very bright");
  }

  delay(100);
}
```

## Step 4: Upload the Code

1. **Connect the Board**

* Connect your GLYPH board to your computer

2. **Select the Board and Port**

   Do the following settings in your Arduino IDE,

   * Tools > Board > esp32 > Pcbcupid GLYPH C6

<Warning>
  For the `Pcbcupid GLYPH C6` to appear under Tools > Board > esp32, the esp32 board version installed in the Arduino IDE should be greater or equal to 3.1.0.
</Warning>

* Tools > Port and select the port connected to your GLYPH.
* Tools > USB CDC on Boot > **Enabled**

<Warning>
  If USB CDC on BOOT is not enabled, you won't see any serial data in the Arduino IDE.
</Warning>

3. **Upload the Code**

Upload the corresponding code for your board to the GLYPH board using the Arduino IDE.

* Click the upload button (➡ icon) or use the shortcut CTRL + U in Arduino IDE to upload the code to the board.

## Step 5: Observe the Serial Monitor Output

Try covering and uncovering the LDR with your hand to block and pass light, and observe the output on the Serial Monitor.

![pcbcupid\_ldr\_serial\_output](https://files.pcbcupid.com/Documentation/Boards/Examples/ldr/ldr_glyph_screenshot.avif)