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IR Sensor Ring (v1)

A ring of 12 infrared receivers that tells your robot which direction the RoboCup Junior Soccer ball is in, and how strong its signal is, all the way around the robot.

At a glance

  • Measures: IR ball direction (12 sectors, or 0–360°) and signal strength
  • Connects to: LEGO® SPIKE™ Prime hub, any port (shows up as a colour sensor)
  • Firmware: IRRingFirmware from the AdvancedBotWorks library
  • Shop: advancedbotworks.com

Channel outputs

Channel Meaning Range Units Notes
Red (R) Simple direction 0–12 sector Which of the 12 receivers sees the strongest signal (numbered 1–12 around the ring, see Mounting). 0 = no ball detected
Green (G) Signal strength 0–100 – The share of samples in which the strongest receiver saw the ball. Higher usually means closer
Blue (B) Advanced direction 0–360 degrees Smoothed angle, interpolated from the neighbouring receivers. 0 when no ball is detected

Simple vs advanced direction

Simple direction (R) jumps in 30° steps, one per receiver, and is the easiest to use for a basic "chase the ball" program. Advanced direction (B) blends the readings of the receivers either side of the strongest one, giving a smoother angle for more precise steering.

The 12 receivers are spaced 30° apart, so sector n in simple direction corresponds to roughly n × 30° in advanced direction. Check which way receiver 1 faces on your sensor before mounting it (see Mounting).

Quick start

  1. Mount the ring flat and centred on your robot, with receiver 1 facing your robot's front.
  2. Plug the cable into any hub port.
  3. Read R, G and B (see Getting started). Move the ball around the robot and watch the direction change.

Example code

Add the More Sensors extension, then use the Color Sensor red block for the simple direction, green for strength and blue for the advanced direction.

from hub import port
import color_sensor, runloop

async def main():
    while True:
        direction, strength, angle, _ = color_sensor.rgbi(port.A)
        if direction == 0:
            print("No ball")
        else:
            print("Ball in sector", direction, "at", angle, "deg, strength", strength)
        await runloop.sleep_ms(50)

runloop.run(main())

Specifications

Physical
Dimensions TBC mm
Weight TBC g
Mounting Fits the LEGO® stud/pin grid (hole spacing TBC)
Cable Attached cable with SPIKE Prime connector, length TBC

Electrical
Supply From the SPIKE hub port
Current draw TBC mA
Microcontroller Microchip ATSAMD21G18A (ARM Cortex-M0+, 48 MHz)
IR receivers 12 × Vishay TSSP77038 (38 kHz), 30° apart
USB USB port on the board for firmware updates (see Updating firmware)

Performance
Ball type Tuned for the RoboCup Junior Australia pulsed IR ball. Testing with the ball chosen for 2027 is in progress
Direction resolution 12 sectors (simple) / interpolated angle (advanced)
Update rate Not yet fixed. Each update takes 100 samples of all 12 receivers, so the rate depends on loop timing. A fixed, documented rate is planned
Detection range TBC (to be measured with the RCJA and 2027 balls)

In the box

  • 1 × IR Sensor Ring with attached SPIKE Prime cable

Mounting

The ring fits the LEGO® stud/pin grid. Mount it level, away from motors and metal that could block the receivers, and above other parts of the robot so nothing shadows the ball.

Mounting diagram coming soon.

Firmware

Known limitations

  • Other 38 kHz IR sources (some remote controls, other robots' IR, strong sunlight) can interfere with readings.
  • Strength isn't a calibrated distance. It depends on the ball, its battery level and the environment.
  • The update rate isn't fixed yet (see Performance above).

Revision history

Version Date Changes
v1 2024-06 First release (firmware library 1.0.0)

Still to confirm

  • Dimensions, weight, hole spacing and cable length
  • Current draw
  • Detection range (RCJA ball and 2027 ball)
  • Which way receiver 1 faces, and whether numbering runs clockwise (mounting diagram)
  • Measured update rate