LDR (Light Sensor) with NodeMCU

 LDR (Light Dependent Resistor) is a popular light sensor, and its applications are the most diverse, as for example in streetlights, lighting lamps at night, when dark, and switching off during day, when light. Now let's see how to connect this sensor to NodeMCU.

Figure 1 - LDR and NodeMCU

The sensor

The LDR is a resistor that varies in proportion to the lighting it receives, meaning that depending on the luminosity the value of the internal resistance in Ohm (R|Ω) will vary, from virtually 0R, when under strong light, to about 200kR when in full darkness.

The circuit

Understanding that the LDR is a resistor, and can virtually reach 0R, all we need is an NodeMCU analog port ( Note your NodeMCU card, the ESP8266 version has only one analog input, while the ESP32 version has 15, adapt the circuit or the input port in the code if necessary) and a 100kR resistor to create a  Voltage Divider  and thus we can read the voltage, in this case it varies from 0V (0 in reading), when in total darkness up to 5V (1023 in reading, considering a 10-bit card with analog input resolution), when in great light. Necessary material:

• 1x - Arduino
• 1x - Protoboard
• 1x - LDR
• 1x - 100kR resistor

Figure 2 - Circuit with LDR and NodeMCU

The code

Basicamente o código imprime se "está escuro", caso a tensão recebida esteja abaixo da metade do limiar e "está iluminado" se igual ou acima do limiar.