Sensors

Sensors

• Introduction
• The five senses
• Which page do I want
• What every sensor has in common
• Testing a sensor before you trust it

Introduction

This is the overview page for everything Otto can perceive. Each sensor has its own page with the full story; this one is the map, plus the habits that apply to all of them.

The five senses

Facade	Module	Hardware	Needs enabling
Eyes	Ultrasonic	HC-SR04 distance sensor	No
Touch	TouchSensor	TTP223 touch pad, or a push button	No
Ears	SoundSensor	Analog microphone	No
--	LightSensor	Photoresistor (LDR)	No
Balance	Mpu6050	MPU-6050 / GY-521 motion sensor	Yes

Sensors on analog and digital pins need no initialisation: an unconnected pin simply returns noise, and the call is harmless. The MPU-6050 is the exception -- it speaks I2C, and must be enabled in the configuration.

Which page do I want

• Eyes -- distance to whatever is in front: obstacle avoidance, follow-me, "is someone there".
• Touch -- a tap or a held finger: start a behaviour, toggle a mode.
• Ears -- loudness: clap detection, reacting to a room getting noisy.
• Light -- brightness: sleep in the dark, wake in the light.
• Balance -- tilt and shake: is Otto level, upside down, being picked up.

What every sensor has in common

Three habits carry across all five, and each is covered in depth on its own page:

• Prefer the question to the number. Eyes::closerThanCm(15) and Ears::hearsSoundLouderThanPercent(60) read as sentences and keep thresholds visible. Reach for the raw value when you need to compare it against several things at once.
• Find thresholds empirically. Every percentage on these pages depends on your hardware, your room, and in the microphone's case a physical gain pot. Measure first in the console, then choose.
• Reading takes time. A distance ping waits for an echo; a loudness reading listens for a 50 ms window. Sensor calls are not free, and while a movement call is blocking, nothing is being sensed at all.

Testing a sensor before you trust it

Do not debug a sensor from inside a behaviour. Bring it up on its own in the Serial Console:

> dist
23 cm
> touch
touched
> light
64 %
> mic
12 %
> tilt
pitch -1.4  roll 0.8
> watch mic

watch streams a sensor live and prints only when the value actually changes, so you can wave a hand or clap and watch the numbers follow. It is the fastest way to tell a miswired sensor from a badly chosen threshold -- and the two look identical from inside a sketch.