Recommended Components for NodeMCU Experiments

Experimental components include: LED, switch and temperature and humidity sensor.

1. Connection of LED

LED (Light Emitting Diode) is a solid-state semiconductor device that can convert electrical energy into visible light. It directly converts electricity into light. The core of the LED is a semiconductor chip, one end of which is attached to a bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply, encapsulating the entire chip in epoxy resin.Note: The longer leg is the positive electrode, and the shorter leg is the negative electrode.

When the current flowing through the LED exceeds its limit, it may burn out, so generally, circuits require a current-limiting resistor. Please calculate the minimum value of the current-limiting resistor based on the formula. Refer to the circuit connection diagram.

Current-limiting resistor = (Power supply voltage – LED forward working voltage) / LED working current

LED wiring reference diagram

2. Connection of switch components

The GPIO port of the microcontroller may be an uncertain signal in the initial state, which may cause misoperation. To overcome this situation, a pull-up resistor can be added to clamp the port level at a high level, or a pull-down resistor can be added to clamp the port level at a low level, avoiding false triggering. The function of the pull-up or pull-down resistor is to fix the uncertain signal at a high/low level through a resistor, which also serves to limit the current. The reference diagram for the switch connection is as shown. Generally, a pull-up or pull-down resistor can be chosen at 10kΩ.

Pull-up resistor switch connection diagram

Pull-down resistor switch connection diagram

3. DHT11 temperature and humidity sensor

The DHT11 is a composite sensor with calibrated digital signal output for temperature and humidity. It uses specialized digital module acquisition technology and temperature and humidity sensing technology to ensure reliability and excellent long-term stability, low cost, relative humidity and temperature measurement, fast response, strong anti-interference ability, long signal transmission distance, digital signal output, and precise calibration.

The sensor includes a resistive humidity sensing element and an NTC temperature sensing element, connected to a high-performance 8-bit microcontroller. It can be used in HVAC, dehumidifiers, testing and detection equipment, consumer products, automobiles, automatic control, data loggers, meteorological stations, home appliances, humidity regulators, medical and other related temperature and humidity detection and control.

Functional features:

1. Can detect the humidity and temperature of the surrounding environment 2. Humidity measurement range: 20%-95% (0 degrees – 50 degrees range) Humidity measurement error: ±5% 3. Temperature measurement range: 0℃-50℃, temperature measurement error: ±2℃ 4. Operating voltage 3.3V-5V 5. Output form: digital output 6. Power indicator light (red)

Module interface description (3-wire system): 1. VCC connects to 3.3V or 5V 2. GND connects to GND 3. out is the DHT11 switch digital output interface, connected to the IO port of NodeMCU

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