ESP32-S3 board
The brain that runs your uploaded sketch.
01 First, know the pieces
What you need
The same six things as Day 6 — you may already have them wired. Tap Define on any part you haven't met; the answer opens as a field note you can read and dismiss without losing your place.
GPIO extension board
Spreads the pins into rows you can reach and label.
LED bar graph
The same strip from Day 6 — ten small LEDs, each its own segment.
8 × 220 Ω resistors
One in series with each driven segment to keep every current gentle.
Jumper wires
Temporary, solder-free connections.
Arduino IDE
Uploads the sketch to the board.
02 Make the physical circuit
Chart the circuit
This is the same LED bar circuit you built on Day 6 — if it's still on the breadboard, you're nearly done. The one difference is that today's sketch drives eight of the segments, because each needs its own PWM channel and the board has eight, so two segments stay dark.
8 bar segments (via 220 Ω each)
→GPIO 21 47 38 39 40 41 42 2
Each pin drives one segment with its own PWM channel.
Bar common row
→GND
Returns every segment to zero volts.
The bar can go in backwards. The LED bar's label direction is easy to reverse. If the driven segments stay dark once you upload, rotate it 180° in the breadboard and try again. Unplug USB before you move any wire.
03 One action at a time
Build it
This is the main path — you can finish the day without opening a single field note. Tap each step as you go to keep your place.
0 / 6 done
Confirm the Day 6 LED bar is still wired, or rebuild it — LED bar across the centre channel, one 220 Ω resistor per segment, common row to ground.
Keep USB unplugged while you check or move any wire.
Note that only eight segments are wired for PWM today, since the board has eight PWM channels; two segments stay dark on purpose.
Compare every wire to the chart before you plug in USB.
Open
Sketch_04.2_FlowingLight2.inoin Arduino IDE and upload it.Watch a bright segment with a fading tail glide along the bar and back.
04 Read just enough code
Read the code
The sketch keeps the pins in one list, like Day 6, but adds a second list of brightness values that forms the tail. Switch to MicroPython if you'd rather see the same idea in Python — the wiring never changes.
const byte ledPins[] = {21, 47, 38, 39, 40, 41, 42, 2};
const byte chns[] = {0, 1, 2, 3, 4, 5, 6, 7};
const int dutys[] = {0,0,0,0,0,0,0,0, 1023,512,256,128,64,32,16,8, 0,0,0,0,0,0,0,0};
void setup() {
for (int i = 0; i < 8; i++) {
ledcAttachChannel(ledPins[i], 1000, 10, chns[i]);
}
}
void loop() {
for (int i = 0; i < 16; i++) {
for (int j = 0; j < 8; j++) {
ledcWrite(ledPins[j], dutys[i + j]);
}
delay(100);
}
}ledcAttachChannel(ledPins[i], 1000, 10, chns[i])Gives each of the eight pins its own PWM channel, so every segment can hold a brightness of its own. const int dutys[] = {0,..., 1023,512,256,128,64,32,16,8, ...,0}A brightness gradient — bright to dim — with dark padding on each side; those falling numbers are the fading tail. ledcWrite(ledPins[j], dutys[i + j])Reads an eight-wide window of the gradient and slides it one step each pass, which is what makes the comet move. Optional side path · same circuit
mypwm = myPWM(21,47,38,39,40,41,42,2)
chns = [0,1,2,3,4,5,6,7]
dutys = [0,0,0,0,0,0,0,0, 1023,512,256,128,64,32,16,8, 0,0,0,0,0,0,0,0]mypwm = myPWM(21,47,38,39,40,41,42,2)A helper wraps each of the eight pins as a PWM object so they can hold brightness in Python.dutys = [...1023,512,256,128,64,32,16,8...]The same falling gradient as the Arduino sketch — the head is brightest and the tail fades.A helper pwm.py wraps each pin as a PWM object. Run it in Thonny if MicroPython is set up; otherwise skip it — it should never block the Arduino-first path.
05 Understand, don't memorise
A gradient that moves
There's no trick here — the board sets eight brightnesses at once, then nudges the whole pattern along the bar, faster than the eye separates the steps.
PWM per LED
Each segment gets its own channel so it can be bright or dim.
bright to dim
The dutys list falls from full on down to a faint glow.
one step
An eight-wide window of that list moves one place each pass.
head and tail
The bright end leads and the dim end trails it down the bar.
The model
eight brightnesses → a falling gradient → slide it one step → head leads, tail fades
What PWM is doing
PWM flicks each pin on and off very fast; the fraction of time it stays on sets how bright that segment looks, so a whole row can carry a smooth gradient.
06 Know it worked
Test & debug
Nothing prints to the screen today — the proof is the moving comet on the bar.
What you should see
- A bright segment leads with dimmer segments trailing behind it.
- The bright head and its fading tail glide along the bar together.
- Then the comet slides back the other way, smoothly, for as long as the board has power.
Two segments stay dark on purpose — only eight are on PWM, because the board has eight PWM channels.
If it doesn't
- Only one segment lights, with no tail? You may be running Day 6's on/off sketch — upload 04.2 so PWM sets the brightnesses.
- A segment in the path stays dark? Check that segment's own 220 Ω resistor and its jumper to its GPIO pin.
- Nothing lights at all? Re-check the common row to ground, then that the sketch uploaded.
- Upload fails? Swap in a data-capable USB cable.
07 Make the idea yours
Try this: reshape the comet
Same working circuit, small edits to the sketch. Both fit inside today's time and leave the wiring untouched.
Reshape the tail
Edit the falling numbers in dutys — add more dim values for a longer tail, or fewer for a shorter one. Predict the shape before you upload.
Change the speed
Set delay(100) to a larger or smaller number and upload. Find the speed where the comet still reads as one moving light.
Logbook
08 Learn it with a hand on the tiller
Coach me through it
Every lesson ships with a code and a machine-readable packet, so an agent can guide you with full context.
Lesson code
TSK-DAY08-METEOR
Context packet
How the agent should behave: confirm the Day 6 circuit first, guide one segment at a time, wait for you to confirm, explain terms on request, and always check wiring, board, port, and USB before changing code.