Sensors

A sensor is a transducer — it converts a physical phenomenon into an electrical signal or digital data that a microcontroller can read.

Choosing the right sensor for your object is a design decision. It shapes what your object is sensitive to, and therefore what kind of presence it has in the space.

Sensor Types Relevant to This Course

Motion & Presence

PIR (Passive Infrared) — detects body heat moving through its field of view. Good for detecting whether someone is in a space. Binary: presence or absence.

Ultrasonic distance (e.g. HC-SR04) — measures distance to the nearest object using sound pulses. Good for proximity detection. Range: 2cm–80cm.

Time-of-Flight (e.g. VL53L0X) — more accurate distance sensing using laser. Compact, precise. Range: 5cm-4m.

Touch & Pressure

Capacitive touch — detects the proximity of a hand or finger without physical contact. Good for surfaces.

Force-sensitive resistor (FSR) — changes resistance under pressure. Good for weight, squeeze, push.

Piezoelectric — generates a voltage when physically deformed. Good for detecting vibration or impact.

Environment

Light (LDR / photoresistor) — changes resistance with ambient light level. Simple, cheap, effective.

Sound (microphone / MAX4466) — measures ambient sound level. Feeds back into your sound system — be careful with feedback loops.

Temperature (e.g. DS18B20, DHT22) — measures ambient or surface temperature. Slow-changing, good for gradual drift.

Humidity (e.g. DHT22) — often paired with temperature.

Orientation & Movement

IMU / Orientation (e.g. BNO085) — measures acceleration, rotation, heading, pitch, and roll. Good for detecting tilt, shake, or movement. The BNO085 gives stable orientation as quaternions.

Choosing a Sensor for Your Object

Ask:

What does this object do in its normal life? (A door opens. A cup is lifted. A chair is sat on.)
What physical change accompanies that action?
Which sensor type captures that change?
What is the range of values the sensor will produce? (0–1? 0–1023? -1g to +1g?)