Introduction to Python and Microcontrollers

Night Lamp

Make an LED automatically brighten in the dark and dim in bright light, using a photoresistor to sense ambient light — an automatic night lamp.

New Concepts

• Photoresistors (LDRs)
• Voltage dividers as a sensing technique

Photoresistor

A photoresistor (LDR) is a light-sensitive resistor — its resistance drops as more light hits its surface, and rises in the dark.

Voltage dividers

Pairing it with a fixed resistor in a voltage divider turns that resistance change into a voltage change, which the ADC can read.

As ambient light changes, the photoresistor’s resistance changes, which shifts the voltage measured between it and the fixed resistor.

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Component List

Circuit

Wiring Diagram

Disconnect all power before building the circuit. Reconnect once verified.

Connections:

• 3.3V → 10kΩ resistor → GPIO1 → photoresistor → GND
• LED anode → 220Ω resistor → GPIO14
• LED cathode → GND

Schematic Diagram

Code

File: 03_sensors/code/NightLamp.py

from machine import Pin,PWM,ADC
import time

pwm =PWM(Pin(14,Pin.OUT),1000)
adc=ADC(Pin(1))
adc.atten(ADC.ATTN_11DB)
adc.width(ADC.WIDTH_12BIT)

def remap(value,oldMin,oldMax,newMin,newMax):
    return int((value)*(newMax-newMin)/(oldMax-oldMin))

try:
    while True:
        adcValue=adc.read()
        pwmValue=remap(adcValue,0,4095,0,1023)
        pwm.duty(pwmValue)
        print(adcValue,pwmValue)
        time.sleep_ms(100)
except:
    adc.deinit()
    pwm.deinit()

This is the exact same code as Soft Light — only the sensor wired to GPIO1 has changed.

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How to Run

Online

1. Open Thonny → 03_sensors/code/.
2. Double-click NightLamp.py.
3. Click Run current script. Cover the photoresistor with your hand, or shine a light on it — the LED’s brightness changes in response.

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Code Explanation

Since the circuit and code are logically identical to Soft Light, see Soft Light’s Code Explanation for a full walkthrough of remap() and the ADC → PWM pipeline. The only conceptual difference: the ADC value now reflects ambient light level instead of a knob’s position, and because the photoresistor’s resistance drops in bright light, more light produces a lower voltage on GPIO1 — which remaps to a lower PWM duty, dimming the LED in bright conditions and brightening it in the dark.

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Key Concepts

• Photoresistor (LDR): a resistor whose resistance changes with light intensity
• Voltage divider sensing: pairing a variable resistor with a fixed one converts a resistance change into a readable voltage change
• Reusing code: the same ADC → remap() → PWM code from Soft Light works unchanged with a different sensor, because both produce a 0–4095 ADC reading

See Class ADC and Class PWM(pin, freq) for the full API reference.

Further Exploration

• Invert the brightness response (LED dims in the dark instead).
• Add a threshold so the LED only turns on below a certain light level, instead of dimming continuously.

Back to Module

Adapted from Python_Tutorial.pdf Project 11.1

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