ESP32 S3 UNO - LDR Module

Hardware Preparation

Or you can buy the following kits:

Overview of LDR Light Sensor Module

An LDR light sensor module tells your board how bright the room is. It is a small board with a light-dependent resistor, a comparator chip and a potentiometer. You can use it as an on/off light detector, as a light level meter, or as both at the same time.

Pinout

The module has four pins. Two of them power the board, and the other two carry the light signal.

The module also has two small LEDs. The PWR-LED turns on when the module has power. The DO-LED follows the DO pin: it is on when the module sees light and off in the dark.

How It Works

The two outputs work in different ways, so it helps to know what each one does before you write code.

DO pin (digital)

The potentiometer on the module sets a light threshold. When the light around the sensor is brighter than this threshold, the DO pin goes LOW and the DO-LED turns off. When the light is weaker than the threshold, the DO pin goes HIGH and the DO-LED turns on.

AO pin (analog)

The AO pin gives a voltage that follows the light level. More light means a lower reading, and less light means a higher reading. The potentiometer has no effect on the AO pin. It only moves the threshold for the DO pin.

So you can tune the DO pin for a simple yes/no light check, and still read the exact light level from the AO pin.

ESP32 S3 Uno Pinout

The image below shows the pinout of the ESP32 S3 Uno form board. Use it to find the Uno header pins (D2, A0…) and their GPIO numbers while you wire the sensor.

Wiring Diagram

The module has two outputs, and you can use one of them or both. The diagram connects DO to D2 and AO to A0, so both sketches below work without changing any wire.

This image is created using Fritzing. Click to enlarge image

ESP32 S3 Uno Code - Read value from DO pin

This sketch reads the DO pin on D2 (GPIO18) many times per second. It prints whether light is present or not to the Serial Monitor.

Detailed Instructions

Do these steps in order:

1. New to the ESP32 S3 Uno? Follow ESP32 S3 Uno - Getting Started first.
2. Wire it up as shown in the diagram.
3. Connect the board to your computer with a USB Type-C cable.
4. Open Arduino IDE, choose the ESP32S3 Dev Module board and the correct COM port.
5. Copy the code above and paste it into Arduino IDE.
6. Upload the code by clicking the Upload button.
7. Test the sensor by covering the LDR with your hand, then taking your hand away.
8. Open the Serial Monitor and check the result.
9. Tip: If the DO-LED stays on all the time, or stays off even in bright light, turn the potentiometer slowly until the LED changes state at the light level you want.

Now you have a working light detector. You can change the code to turn on an LED or a lamp when it gets dark, or to move a servo motor. The related tutorials at the end of this page show you how.

ESP32 S3 Uno Code - Read value from AO pin

This sketch reads the AO pin on A0 (GPIO2) and prints the raw light value. On the ESP32 S3 Uno the value goes from 0 to 4095, because the ADC is 12-bit. A small number means bright light, and a big number means dark.

The sketch calls analogSetAttenuation(ADC_11db) in setup(). By default, the ESP32 S3 Uno ADC can only measure a small voltage. The 11 dB setting lets the analog pin read the full range, from 0V up to about 3.3V. Without it, the reading hits 4095 too early and the light values look wrong.

Detailed Instructions

1. Copy the code above and open it in Arduino IDE.
2. Upload the code by clicking the Upload button.
3. Cover and uncover the LDR with your hand or an object.
4. Open the Serial Monitor and watch the numbers change.
5. Tip: Write down the values you get in your room, both bright and dark. Use them later as thresholds in your own code.

Video Tutorial

Watch the video below to see this ESP32 S3 Uno project step by step.

The demo in the video uses the code below. It reads the AO pin, smooths the value with a simple filter (EMA), and fades an extra LED on D9 (GPIO46) brighter as the room gets darker. The thresholds are set for the 12-bit ADC (0 to 4095).

Function References

• pinMode()
• digitalRead()
• analogRead()
• Serial

FAQ

Can I power the LDR module from 5V on the ESP32 S3 Uno?

The module itself works at 5V, but its DO and AO outputs then swing up to 5V. ESP32 S3 Uno pins are 3.3V only and are not 5V tolerant. Power the module from the 3.3V pin, and both outputs stay in a safe range.

Why do I get values up to 4095 instead of 1023?

The ESP32 S3 Uno has a 12-bit ADC, so analogRead() returns 0 to 4095. Boards like the UNO R4 use 10-bit by default and return 0 to 1023. If you copy thresholds from an UNO R4 project, multiply them by about 4.

Why does the code call analogSetAttenuation(ADC_11db)?

It sets the ESP32 S3 Uno ADC input range to about 0V to 3.3V, so the full light sensor signal maps to 0 to 4095. Without it the range is smaller, and the readings jump to 4095 even in normal room light. The UNO R4 does not need this line, because it is ESP32-only. Keep the AO voltage at 3.3V or less.

Should I use the DO pin or the AO pin?

Use the DO pin when you only need to know "light or dark", for example for a night light. Use the AO pin when you want a light level number, for example to dim an LED step by step. You can wire both at the same time.

Is the LDR module accurate enough to measure lux?

No. An LDR gives a relative value that depends on the part, the temperature and the supply voltage. It is great for detecting light and dark. For real lux values, use a digital light sensor such as the BH1750.

What if my project needs more pins than the Uno headers give?

The ESP32 S3 Uno has two extra rows of holes with more GPIOs: GPIO15 and GPIO16 (I/O, PWM, analog), GPIO45 and GPIO35 to GPIO42 (I/O, PWM), and GPIO47/GPIO48 (output only, PWM). Solder pin headers to use them and write the GPIO number in your code. For a second LDR module, use GPIO15 or GPIO16 for the AO pin, and GPIO35 to GPIO42 for the DO pin. Do not use GPIO47/GPIO48 as sensor inputs. Two warnings: (1) GPIO47/GPIO48 may run at 1.8V instead of 3.3V on some modules (especially ones with "V" in the name, like R8V or R16V), so 3.3V devices can be damaged or act strangely. (2) GPIO0, GPIO3 (D6), GPIO45 and GPIO46 (D9) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code. Use the other extra pins first.

Troubleshooting

Learn More

• ESP32 S3 UNO - Light Sensor
• ESP32 S3 UNO - Light Sensor Controls LED
• ESP32 S3 UNO - Light Sensor Controls Relay
• ESP32 S3 UNO - Light Sensor Controls Servo Motor