KY-054 Phototransistor Module
The KY-054 is a phototransistor module that detects ambient light levels and provides an analog voltage output proportional to the light intensity. It is commonly used in projects that require light sensing capabilities, such as automatic lighting systems and brightness detection.
KY-054 pinout
The KY-054 is a 3-pin phototransistor light detection module:
| Pin | Type | Description | Notes |
|---|---|---|---|
| GND | Power | Ground connection | |
| +V | Power | Power supply | 3.3V or 5V |
| Signal | Communication | Analog output | Voltage proportional to light intensity |
Interface: Analog output (light intensity measurement)
Sensor: Phototransistor (faster than LDR)
Output: Voltage varies with ambient light level
Power: 3.3V or 5V operation
Response: Faster response time than LDR sensors
Applications: Ambient light detection, automatic brightness control, light-triggered systems
Wiring the KY-054 to ESP32
To interface the KY-054 with an ESP32 for light intensity measurement:
| KY-054 pin | ESP32 pin | Purpose |
|---|---|---|
| GND | GND | Ground |
| +V | 3.3V or 5V | Power supply |
| Signal | GPIO36 | Analog input (ADC pin) |
ADC Pins: Use GPIO32-39 for analog input on ESP32
Voltage: 3.3V recommended for ESP32 ADC compatibility
Light Level: Higher light = higher voltage output
Faster Response: Phototransistor responds quicker than LDR/photoresistor
KY-054 code examples
// Define pin for phototransistor
int light_sensor = 36; // GPIO36 / ADC1_CH0, matches the wiring above
// Definition of the parameters required for the calculation
const double U1 = 3.3; // Supply voltage (ESP32: 3.3V)
const double R2 = 10000.0; // Series resistor
double U2;
double I;
double R1;
double lux;
int rawValue;
void setup() {
Serial.begin(115200);
Serial.println("KY-054 Brightness test");
}
void loop() {
// Reading the voltage of the light sensor (ESP32: 12-bit ADC, 3.3V)
rawValue = analogRead(light_sensor);
U2 = rawValue * (3.3 / 4095.0);
// Check U2 for the division
if (U2 != 0) {
// Calculate the resistance of the sensor
R1 = (U1 * R2) / U2;
// Calculate current
I = (U1 / R1) * 1000000.0;
// Calculate lux
lux = log(I) / 0.06;
}
else lux = 0;
// Output the result on the serial monitor
Serial.print("Lux:\t");
Serial.println(lux);
// wait for one second
delay(1000);
}This Arduino code sets up the KY-054 phototransistor module to measure ambient light intensity. It reads the analog voltage from the sensor, calculates the corresponding lux value using a logarithmic formula, and outputs the result to the serial monitor every second.
#include <stdio.h>
#include <math.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
#include "driver/adc.h"
#define LIGHT_ADC_CHANNEL ADC1_CHANNEL_0 // GPIO36, matches the wiring above
void app_main(void)
{
adc1_config_width(ADC_WIDTH_BIT_12);
adc1_config_channel_atten(LIGHT_ADC_CHANNEL, ADC_ATTEN_DB_11);
const double U1 = 3.3; // supply voltage
const double R2 = 10000.0; // series resistor
while (1) {
int raw = adc1_get_raw(LIGHT_ADC_CHANNEL);
double U2 = raw * (3.3 / 4095.0);
double lux = 0;
if (U2 > 0) {
double R1 = (U1 * R2) / U2; // phototransistor resistance
double I = (U1 / R1) * 1000000.0; // current in microamps
lux = log(I) / 0.06; // approximate lux conversion
}
printf("Lux: %.1f\n", lux);
vTaskDelay(pdMS_TO_TICKS(1000));
}
}The phototransistor's output is read on GPIO36 (ADC1 channel 0) with 11 dB attenuation for the full 3.3 V range. From the measured voltage the code derives the phototransistor's resistance in the 10k divider, converts it to a current, and applies the module's approximate logarithmic lux formula - fine for relative brightness; calibrate against a lux meter for absolute accuracy.
sensor:
- platform: adc
pin: GPIO36
name: "KY-054 Light Sensor"
update_interval: 1s
filters:
- multiply: 3.3
- lambda: |-
float resistance = (3.3 * 10000.0) / (x == 0 ? 1 : x);
float current = (3.3 / resistance) * 1000000.0;
return log(current) / 0.06;This ESPHome configuration sets up the KY-054 phototransistor module on GPIO36 as an analog input. It reads the voltage level, applies a mathematical conversion to estimate light intensity in lux, and updates the value every second.
[env:esp32]
platform = espressif32
board = esp32dev
framework = arduino#include <Arduino.h>
#define LIGHT_SENSOR_PIN 36
void setup() {
Serial.begin(115200);
Serial.println("KY-054 Light Sensor Test");
}
void loop() {
int raw_value = analogRead(LIGHT_SENSOR_PIN);
float voltage = raw_value * (3.3 / 4095.0);
Serial.printf("Light Sensor Voltage: %.2fV\n", voltage);
delay(1000);
}This PlatformIO code configures GPIO36 as an analog input for the KY-054 sensor. It reads the analog voltage, converts it to a readable format, and prints it to the serial monitor every second.
import machine
import time
import math
LIGHT_SENSOR_PIN = machine.ADC(machine.Pin(36))
LIGHT_SENSOR_PIN.atten(machine.ADC.ATTN_11DB)
while True:
raw_value = LIGHT_SENSOR_PIN.read()
voltage = (raw_value / 4095) * 3.3
resistance = (3.3 * 10000.0) / (voltage if voltage > 0 else 1)
current = (3.3 / resistance) * 1000000.0
lux = math.log(current) / 0.06
print("Light Intensity:", lux, "lux")
time.sleep(1)This MicroPython script sets up the KY-054 phototransistor module on GPIO36 as an analog input. It reads the sensor voltage, calculates the resistance, estimates the light intensity in lux, and prints the value every second.
KY-054 specifications
About the KY-054
The KY-054 uses an HLPT550B5H5 NPN silicon phototransistor rather than the cadmium-sulfide photoresistor on the KY-018, wired the same way - as one leg of a voltage divider against a fixed 10 kOhm resistor, so the ESP32 still reads a light-dependent voltage rather than anything calibrated to lux. The practical difference is speed and behavior: a phototransistor’s collector current tracks incident light in microseconds and follows a more predictable curve than a CdS cell’s resistance, which can take tens of milliseconds to settle and swings non-linearly over several orders of magnitude between dark and bright. Being silicon rather than cadmium-based also sidesteps the RoHS restrictions that increasingly apply to CdS photoresistors like the KY-018.
None of that makes the raw reading an accurate lux meter - treat it, like the KY-018, as a relative brightness signal for thresholds and day/night logic rather than an absolute measurement, and calibrate against a real lux meter if a project needs actual light-level numbers. On the wiring side the signal pin belongs on one of the ESP32’s ADC1 pins (GPIO32-39) as shown above, since ADC2 shares hardware with the WiFi radio and stops working reliably once WiFi is active.
KY-054 troubleshooting
No Response from the Sensor
›
Issue: The sensor does not provide any output or the readings remain constant.
Solutions:
- Ensure that the module is properly powered with the correct voltage (3.3V or 5V).
- Verify that all connections are secure and correctly oriented.
- Check if the analog input pin on the microcontroller is functioning correctly by testing with another analog sensor.
Inaccurate or Fluctuating Readings
›
Issue: The sensor provides erratic or incorrect light intensity values.
Solutions:
- Avoid exposing the sensor to direct light sources that may cause saturation.
- Implement software filtering techniques, such as averaging multiple readings, to smooth out fluctuations.
- Ensure that there are no loose connections or interference from nearby electronic components.
Resources
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