John: Claude edited based on my notes, prompt, and SimpleBot code repository

2025-10-11T16:18:40Z

Claude edited based on my notes, prompt, and SimpleBot code repository

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{{Module
| name = Infrared Line Detector Module
| function = Line Following Sensor
| type = Sensor Module
| voltage = 3.3V – 5V
| interface = Digital output (active LOW)
| cost = $0.50 USD (bulk) / $0.75 (single)
}}

The '''Infrared Line Detector Module''' (also called "Infrared Obstacle Avoidance Sensor" or "IR Reflectance Sensor") is a simple digital sensor used for line-following robots. It detects the contrast between light and dark surfaces by measuring reflected infrared light.

== Overview ==

This ubiquitous sensor module consists of an infrared LED and an infrared phototransistor positioned side-by-side. The LED emits IR light, which reflects off the surface below. The phototransistor detects the reflected light, and an onboard comparator (typically LM393) converts the analog signal to a digital output.

The module is designed to detect:
* Black lines on white surfaces (typical for line-following)
* White lines on black surfaces (inverted mode)
* Edges and drop-offs (cliff detection)
* Proximity to obstacles (though range is limited)

== Key Features ==

* '''Simple Digital Output''': HIGH or LOW based on detected surface
* '''Adjustable Sensitivity''': Onboard potentiometer to set detection threshold
* '''Active LOW Output''': Output goes LOW when dark surface detected
* '''Low Cost''': Often sold in packs of 20 for $10 USD
* '''Low Power''': Typically <20mA at 5V
* '''Compact Size''': ~30mm × 15mm typical module size

== Module Components ==

# '''IR LED''': Emits infrared light (typically 940nm wavelength)
# '''IR Phototransistor''': Detects reflected IR light
# '''LM393 Comparator''': Converts analog signal to digital
# '''Potentiometer''': Adjusts detection threshold
# '''Power LED''': Indicates module is powered
# '''Detection LED''': Lights when dark surface detected

== Pin Configuration ==

Typical 3-pin module:
* '''VCC''': 3.3V to 5V power supply
* '''GND''': Ground
* '''OUT''' (or '''DO'''): Digital output (active LOW)

Some modules also provide:
* '''AO''': Analog output (raw sensor voltage, if available)

== How It Works ==

# The IR LED constantly emits infrared light downward
# Light reflects off the surface below
# '''Light surfaces''' (white/reflective) reflect more IR light → phototransistor conducts more → output HIGH
# '''Dark surfaces''' (black/absorptive) reflect less IR light → phototransistor conducts less → output LOW
# The potentiometer adjusts the threshold between "light" and "dark"

== Adjustment Procedure ==

# Power the module
# Place it over a white surface
# Adjust the potentiometer until the detection LED turns OFF
# Move it over a black line
# Verify the detection LED turns ON and output goes LOW
# Fine-tune potentiometer for consistent detection at desired height

Typical detection height: 3mm to 15mm above the surface.

== Usage in BRS Projects ==

[[SimpleBot]] uses two infrared line detector modules for '''line following''':

* '''Mounted on sensor sleds''': Adjustable position under the chassis
* '''Two-sensor configuration''': One on each side of the line
* '''Detection pattern''':
** Both sensors on white → drive straight
** Left sensor on line → turn right
** Right sensor on line → turn left
** Both sensors on line → stop or special behavior

The SimpleBot chassis provides adjustable sensor mounts to fine-tune sensor spacing and height above the ground.

== Wiring Example ==

<pre>
Sensor Module → Microcontroller:
- VCC → 3.3V or 5V
- GND → GND
- OUT → GPIO pin (with internal pull-up enabled)
</pre>

Since the output is active LOW, enable the microcontroller's internal pull-up resistor or add an external 10kΩ pull-up.

== Code Example (MicroPython) ==

<syntaxhighlight lang="python">
from machine import Pin

# Configure line sensors (active LOW)
left_sensor = Pin(10, Pin.IN, Pin.PULL_UP)
right_sensor = Pin(11, Pin.IN, Pin.PULL_UP)

def read_line_sensors():
"""Read both line sensors"""
left_on_line = not left_sensor.value() # Invert because active LOW
right_on_line = not right_sensor.value()

if not left_on_line and not right_on_line:
return "STRAIGHT" # Both on white
elif left_on_line and not right_on_line:
return "TURN_RIGHT" # Left sensor on line
elif right_on_line and not left_on_line:
return "TURN_LEFT" # Right sensor on line
else:
return "BOTH_ON_LINE" # Both on line or at intersection

# Main loop
while True:
state = read_line_sensors()
print(state)
# Add motor control logic here
</syntaxhighlight>

== Limitations ==

* '''Detection Range''': Only works at close range (3-15mm typically)
* '''Ambient Light Sensitivity''': May be affected by bright sunlight or other IR sources
* '''Surface Dependency''': Works best on matte surfaces; glossy or textured surfaces can cause issues
* '''Binary Output''': Digital modules don't provide position information within the line

== Alternatives ==

* '''Analog Reflectance Sensors''': Provide continuous position data (e.g., Pololu QTR sensor arrays)
* '''Color Sensors''': Detect colored lines or surfaces
* '''Camera-Based Vision''': For complex line patterns or multi-colored lines
* '''Custom Sensor Array''': Multiple sensors for better line tracking

== Multi-Sensor Arrays ==

For more sophisticated line following, use multiple sensors (3-8 typical) arranged in a row:
* Better line tracking through curves
* Position calculation within the line
* Intersection and branching detection
* Lost line recovery

== Common Issues ==

* '''No Detection''': Sensor too far from surface or potentiometer needs adjustment
* '''Always Detecting''': Sensor too close or potentiometer too sensitive
* '''Inconsistent Detection''': Ambient IR interference or uneven surface
* '''Slow Response''': Normal for these modules; they're not designed for high-speed line following

== See Also ==

* [[SimpleBot]] - Uses two IR line detectors for line following
* [[Line Following]] - Algorithms and techniques for line-following robots
* [[Optical Odometry]] - Different use of optical sensors for distance measurement

[[Category:Component]]
[[Category:Sensor]]
[[Category:Line Following]]

Infrared Line Detector - Revision history

John: Claude edited based on my notes, prompt, and SimpleBot code repository