Building a Mini Golf Hole Light Show (Raspberry Pi + Pico + WS2812B)

This project was a small, self-contained system designed to detect when a golf ball entered a hole and trigger a preprogrammed LED sequence. The final build used a Raspberry Pi 3B for sensing and control, and a Raspberry Pi Pico for LED driving. This was a fun test of using a SBC to control a microcontroller.

The system is split cleanly into two parts:

Raspberry Pi: reads ultrasonic sensor, determines event, sends command
Pico: listens for commands and renders LED effects

The code used in the final build is here:

Full Project: https://github.com/spjca/miniGolfSinkShow
Pi control + sensor logic: https://github.com/spjca/miniGolfSinkShow/blob/main/testing/ultrasonicTestV12.py
Pico LED controller: https://github.com/spjca/miniGolfSinkShow/blob/main/main.py

Equipment Used

Raspberry Pi 3B
Raspberry Pi Pico
HC-SR04 ultrasonic sensor
WS2812B LED strip (~100 LEDs)
USB cable (Pi ↔ Pico)
External 5V power (recommended for LEDs)

System Layout

The system runs as a loop:

Pi continuously samples distance from ultrasonic sensor
If distance < threshold for consecutive reads → event
Pi sends "celebrate" over serial
Pico switches from idle → animation
After duration, Pico returns to idle

The Pi never directly controls LEDs. It only sends state.

Wiring

1. Ultrasonic Sensor → Raspberry Pi

Pins on HC-SR04:

VCC → Pi 5V
GND → Pi GND
TRIG → GPIO 23
ECHO → GPIO 19 (with voltage divider)

From the code:

TRIG, ECHO = 23, 19

Critical detail: ECHO voltage

HC-SR04 outputs 5V on ECHO
Pi GPIO is 3.3V max

You must use a voltage divider:

ECHO → 1kΩ → Pi GPIO
Pi GPIO → 2kΩ → GND

Without this, you risk damaging the Pi. I rolled the dice and was fine so, do what you will with that.

Behavior

Pi sends a 10µs pulse on TRIG
Measures duration of ECHO high signal
Converts to distance

Raspberry Pi Pico wired up to LED strip for testing

2. Raspberry Pi → Pico (USB Serial)

Connection:

Standard USB cable
Pico appears as /dev/ttyACM0

From the code:

PICO_SERIAL_PORT = '/dev/ttyACM0'
PICO_BAUDRATE = 115200

No GPIO wiring between devices.

Communication model

Pi sends newline-terminated strings:

"idle"
"celebrate"
"off"

Example:

pico.write(f"{message.strip()}\n".encode())

Pico reads from stdin and switches modes accordingly.

3. Pico → WS2812B LED Strip

Connections:

LED VCC → 5V power
LED GND → Pico GND
LED DIN → Pico GPIO 0

From the Pico code:

PIN_NUM = 0
np = neopixel.NeoPixel(machine.Pin(PIN_NUM), NUM_LEDS)

Required electrical details

Shared ground

Pico GND must connect to LED GND
If using external power, grounds must be tied together

Power

100 LEDs at full brightness can draw significant current
In practice, brightness is reduced:

BRIGHTNESS = 0.6

For longer strips or higher brightness, external 5V supply is required.

Optional stability components

Not required in this build, but standard practice:

330Ω resistor on data line
1000µF capacitor across VCC/GND

Detection Logic (Pi)

Core behavior:

Distance threshold: 5 cm
Require 2 consecutive hits
5 second cooldown

DETECT_CM = 5
CONSEC_HITS_N = 2
COOLDOWN_SEC = 5

This avoids:

false triggers from noise
repeated triggers from same ball

Loop behavior:

sample every ~50ms
increment hit streak if under threshold
trigger only if streak condition met

LED Control Logic (Pico)

The Pico runs a simple state machine:

Idle Mode

shimmer_green()

random green values per LED
updated every 100ms
creates undulating effect

Celebration Mode

Triggered by "celebrate" command:

celebrate(duration=8)

Sequence:

Yellow wave across strip
Random white flashes ("paparazzi")
Loop until duration ends
Return to idle

Command Handling

if line == "celebrate":
    current_mode = "celebrate"
    celebrate()
    current_mode = "idle"

All behavior is driven by simple string commands.

Physical Placement

Ultrasonic sensor mounted ~4.5 inches above hole
Pointed straight down
LED strip runs along lane edge

Key constraint:

Distance threshold depends on mounting height
Must be calibrated relative to empty hole vs ball presence

End State

The final system consists of:

one sensor input
one decision loop
one serial interface
one LED controller

No shared state, no complex synchronization, no custom protocol.

The separation between sensing (Pi) and rendering (Pico) allows each part to remain simple and independently adjustable.

Demo

Video: https://youtube.com/shorts/z6JGqtzPrrA?si=_scmMZ1VB6ez1eMX

The video shows the full loop:

idle shimmer
ball enters hole
celebration sequence
return to idle

This reflects the exact behavior implemented in the final code.

Side Quest: Mini Golf Celebration Light Show with a Raspberry Pi 3b and Pico