QTI Line and Close-range Object Detection

The QTI is most often used as a robotic line sensor.  It shines infrared light, and if a surface within about 1/4-inch reflects that light the script will respond with a smaller value.  If the surface is black, it will absorb the light and respond with a larger value.

Parts

(1) QTI module 555-27401 
(1) 3-Pin Signal-Power-Ground Cable Extension (8″) 800-00080 (Optional)
(1) 3-Pin Single Row Header (long) (451-00303) (Optional)
(1) Resistor 220 Ω (red-red-brown-gold)
Jumper wires: Red, black

Schematic

Wiring

Script

# qti-charge-time
from microbit import *
import machine

pin8.set_pull(pin8.NO_PULL)

while True:
    pin8.write_digital(1)
    sleep(1)
    qt = machine.time_pulse_us(pin8, 1, 200000)
    
    s = str(qt) + " us"
    print(s)
    display.scroll(s)

    sleep(100)

Tests

The QTI is designed to face downwards close to either a black or white surface.  Make sure it is not facing a window with sun streaming in or any other bright source of light.

Use a sharpie to create a black 1×1 inch black square in the corner of a sheet of paper.

Face that 1×1 inch black square 1/4 of an inch from the parts side of the QTI and note the measurement.

Now, face a corner the surface of a corner of the same sheet that white, again at a distance of 1/4 inch.

The microsecond time measurement should be less than 1/4 of the previous measurement.