Arduino LDR Voltage Divider for Light Sensing: LED Control Tutorial

This section demonstrates practical PWM circuit implementation using a breadboard and light sensor control. The circuit shows how PWM duty cycle directly affects LED brightness—higher duty cycle means brighter illumination. A photocell (light-dependent resistor) is used as the control voltage source, automatically adjusting brightness based on ambient light levels. When light intensity increases, the photocell resistance decreases, reducing duty cycle and dimming the LED. This creates an automatic brightness control system responding to environmental conditions.

Instead of using a basic Boolean switch widget, use a dim light widget to control LED brightness via pulse width modulation (PWM). This widget allows adjusting brightness levels. Use a dim light variable type instead of Boolean. Implement getBrightness() and getSwitch() functions to handle the brightness adjustment while maintaining on/off functionality.

PWM is the correct method for dimming LEDs. It works by rapidly turning LEDs on and off at frequencies too fast for human eyes to perceive, creating an average dimming effect. Unlike simple voltage reduction, PWM maintains consistent LED color balance because each LED reaches full brightness during its 'on' period.

To dim LEDs using PWM in MobiFlight, connect the LED to a PWM-capable pin (pins 2-13 on Arduino). Configure an analog input module for the potentiometer, storing its value in a MobiFlight variable. Then configure an output module for the LED, enabling PWM mode and mapping the potentiometer's range (typically inverted from 943 to 14) to the PWM range of 0-255 using interpolation modifiers. This creates a smooth brightness adjustment where turning the potentiometer fully clockwise produces maximum brightness (255) and fully counterclockwise produces minimum brightness (0).

A PWM (Pulse Width Modulation) LED dimmer circuit uses a 555 timer IC to generate a switching signal that rapidly turns a MOSFET on and off, controlling LED brightness by varying the duty cycle rather than reducing voltage, which eliminates the power dissipation problems inherent in linear regulators and allows efficient control of high-power LED loads.

To handle environmental variations, implement auto-calibration in code. The approach involves: (1) Collecting sensor data across all surface types, (2) Finding minimum (black) and maximum (white) values programmatically, (3) Setting the threshold between these values. For example, if minimum is 1179 and maximum is 2320, set threshold at 2200. There are three levels of calibration sophistication: (1) Trial and error using website's manual adjustment, (2) Systematic calibration using Excel and analog values, (3) Auto-calibration that calculates thresholds programmatically. The third level is most robust for competitive environments.

Capacitive sensors require threshold calibration to function correctly. The raw sensor value prints to the serial monitor several times per second. As you move your hand closer and further away from the sensor, observe the changing numbers. Set the lower and upper thresholds in the code based on these observed values. Note that capacitive sensors may not work well on battery power, so if using batteries, set 'cap sensor enabled' to false in the code.

Calibration establishes accurate detection thresholds through systematic data collection. Manual calibration should be performed when moving the device to a new bed or during initial setup: turn on calibration, get into bed, wait 30+ seconds for stabilization, then exit and turn off calibration. The system estimates new thresholds based on maximum and minimum pressure values recorded. Auto calibration maintains long-term accuracy by collecting 24 hours of data (every 30 minutes) to adapt to temperature changes, sensor aging, and gradual bed setup shifts. Auto calibration runs at configurable intervals (8-12 hours recommended), using 24 hours of historical data to estimate optimal thresholds. This dual approach ensures consistent accuracy across changing conditions.

The engine control module (ECM) automatically performs a supercharger learn procedure under specific conditions: after startup and once the engine reaches operating temperature at idle. During this process, the ECM commands the turbocharger vane to specific positions while the vane position sensor monitors the actual physical position of the vanes. This self-calibration compensates for inherent offset drift that occurs in sensors and actuators due to normal aging processes. If the resulting calibration values fall outside acceptable ranges, the P003A code will be triggered.

To turn on the meter, press and hold the left side power button. The startup screen shows the self-calibration process and current battery level. After calibration, select the connected antenna type using the right side mode push button, then push and hold the mode button until reaching the measurement screen.

Voltage dividers are widely used with variable resistors (sensors) to convert physical quantities into measurable voltages. Photocells change resistance with light intensity (higher light = lower resistance). Thermistors change resistance with temperature (NTC type: higher temperature = lower resistance). Flex sensors change resistance with bending angle. Force-sensitive resistors change resistance with applied force. The fixed resistor (R1) is chosen based on the sensor's resistance range to maximize the useful output voltage range. Design involves calculating expected Vout values using the divider formula for the sensor's minimum and maximum resistance values.

Voltage dividers convert resistance changes in resistive sensors (like thermistors or potentiometers) into measurable voltage outputs; the output voltage Vout = Vcc × RF / (RF + RT), where RT varies with the physical quantity being measured, and proper selection of the fixed resistance RF relative to the sensor's nominal resistance (R₀) ensures optimal linearity over the desired measurement range.

A voltage divider circuit divides a fixed supply voltage using two resistors—one being a thermistor (whose resistance changes with temperature) and the other a fixed resistor. The output voltage across the fixed resistor is proportional to the ratio of the two resistances. By solving the voltage divider equation algebraically, thermistor resistance can be determined from the measured output voltage. Sensitivity in temperature measurement is defined as the voltage change per unit temperature change, represented by the slope of the output curve. Higher slope magnitudes indicate greater sensitivity, enabling more precise temperature detection.

A resistive sensor changes its electrical resistance when physically deformed (stretched, pressed, or bent), which alters the voltage division in a potential divider circuit; when both sides of the sensor change resistance equally, the voltage reading remains constant, but when only one side changes, the voltage reading shifts proportionally.

Thermistors and LDRs are special resistors whose resistance changes with temperature or light intensity. Thermistors decrease resistance as temperature increases; LDRs decrease resistance as light intensity increases. These enable sensor circuits for temperature control and light detection. A voltage divider uses two or more series resistors to divide input voltage into smaller output voltages. The output voltage is taken across one resistor, allowing any voltage less than the battery voltage to be obtained by choosing appropriate resistance values.

Relay modules serve as electrically operated switches that safely interface low-voltage control circuits with high-voltage AC devices. A 5V relay has three main pins: Common (always connects to one wire of the load), Normally Closed (connects to the other wire when no signal is applied), and Normally Open (connects when the relay is energized). For AC bulb control, one wire from the power cord is cut and connected to the Common pin, while the other connects to Normally Closed or Normally Open depending on desired behavior. The relay requires VCC and GND connections for power and an input pin for the control signal. This isolation protects the Arduino from dangerous AC voltages while enabling automated device control.

A relay is an electromechanical switch that uses a coil to create a magnetic field, which attracts a movable armature to connect or disconnect electrical circuits; when interfacing with Arduino, the relay module's input pins (connected to Arduino pins 12 and 13) control the relay coils, while the load (such as AC bulbs) connects between the common and normally open pins, allowing low-voltage Arduino signals to safely control high-voltage appliances through the relay's isolation capability.

A 5V relay module allows Arduino to safely control AC loads like lamps by using a small control signal to switch higher voltage circuits; the relay has three connection pins (positive, negative, and ground) and three load terminals (normally open contacts), supporting up to 10A at 30V, and requires proper wiring where the load connects to the normally open terminals while the Arduino controls the relay's control pin through code that sets the pin HIGH to activate and LOW to deactivate the relay.

This section explains how to extend the automatic light control system to control AC-powered lamps (220V) using a relay module. The relay acts as an electrically operated switch, connecting to Arduino pin 13 for control. The relay has normally open (NO) contacts that close when pin 13 receives HIGH (5V), connecting the 220V power source to the lamp. When pin 13 is LOW, the relay opens and disconnects the load. This allows the Arduino to safely control high-voltage home lighting using low-voltage digital signals, completing the automatic lighting system.

This section covers relay module operation and complete 220V lighting control systems. A relay module is an electronic switch that allows low-power Arduino circuits to control high-power devices like 220V lights. The relay contains an electromagnet coil that attracts a metal armature, moving a switch between positions. In normally open (NO) mode, the switch connects COM to NO when activated, and disconnects when de-activated. Connect the relay's VCC and GND pins to Arduino's power and ground, and the IN pin to an Arduino output pin for control. Connect the load (light bulb or socket) between COM and NO pins. For multiple lights, use multiple relay modules, each with its own Arduino output pin. Connect the power socket's live wire to COM and neutral wire to NO. When Arduino sends HIGH to the relay's IN pin, the socket receives power and the light turns on. This demonstrates how Arduino can safely control high-voltage household circuits through relay modules.