Project 10 XGO Follows Light

Ⅰ. Teaching Aims

1. Read the value light level (0-100) of the Fox:bit on-board photoresistor.

2. Use map() to linearly map light intensity to step size or speed.

3. Suppress bright and dark jitter through “double thresholds + return difference”.

4. Be capable of independently completing two types of self-developed scripts:

• Bright → Stand up / Dark → sit down

• Light following mode: the brighter the light is, the faster it will walk.

Ⅱ. Pre-class Check

• XGO + Foxbit + MicroBlocks IDE.

• XGO battery power ≥ 60 %. Place the robot on a 1m × 1m flat ground and avoid direct strong light or flickering.

• MicroBlocks status bar shows a green dot, XGO-lite extension is loaded and the development board model is Foxbit.

• Run XGO reset pose and confirm that the zero position and step size are normal.

Ⅲ. Key Blocks Analysis

Functions	Return the ambient light intensity from 0 to 100
Fallible points	Must be placed in forever for real-time reading
Functions	Linear mapping a–b → c–d
Fallible points	a and b cannot be the same
Functions	Determine the light intensity and switch actions
Fallible points	Missing “return difference” → shaking
Functions	Set the forward step size to n mm
Fallible points	Step size > 90 mm → Prone to falling

Comparison table of photosensitivity and step size:

Environment	light level	Recommended step size
Dark room	0 – 10	0(stop)
Ordinary classroom	20 – 40	30 – 50
Beside the desk lamp	60 – 80	60 – 80
Direct flashlight	100+	80 – 90(upper limit)

Ⅳ. Practice

Test 1: Read Real-time Light Intensity (for debugging)

Online code: Click here

Test 2: Stand Up When Bright, Sit Down When Dark

High threshold hiCut = 100, low threshold loCut = 60, return difference 40 lx

Online code: Click here

Test 3: Light Following Dog: Brighter Light for Faster Speed

Online code: Click here

Ⅴ. Quiz

1. Why does Test 2 require “double thresholds” instead of just one?

2. What would happen if the wait 100 ms in Test 3 were changed to 20 ms?

3. Besides photoresistor, what other sensors can you use to “drive” the step size? Please give two examples and explain their mapping range.

Ⅵ. FAQ

Questions	Possible causes	Solutions
Frequent switch between standing up and sitting down	The interval between hiCut and loCut is too small	Return difference ≥ 30 lx
The step size changes randomly	Ambient light flickering	wait ≥ 100 ms, or perform a moving average
Fall while walking	Step size > 90 mm	Set the upper limit of map() to 90
The reading is always either 0 or 100	The sensor is blocked or directly exposed to strong light	Clean the photoresistor holes; Avoid direct light
Response delay	wait is too long	Shorten to 80–120 ms