| | There are many different approaches to build IR (InfraRed) proximity
sensor for the amateur robots. The main problem you can encounter building one, is to
make it insensitive to the ambient infrared radiation. One of the ways to
make it impervious to external light is to use signal modulation. To build
this type of modulator/demodulator pair is not very complicated but not
necessary when we have devices like Sharp
IS471F OPIC (Optical IC) - "light detector with built-in signal
processing circuit for light modulation system".
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The circuit consists of three elements only: the IC,
IR LED 940nm and capacitor 0.33uF. Those elements have been
installed on the small universal PCB with square soldering fields.
To increase sensor accuracy there has been selected LED with low beam
angle (8 degrees) in TO-18 case. |
|
Very important in case of IS471F component is to optically
isolate sensor from IR LED's direct light. This can be achieved
by soldering the IC and LED on the opposite sides of PCB. |
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Since we used universal PCB couple of connections have been
made using wrapping wire. The whole sensor is connected by three
wires: Vcc (+5V), GND and TTL output signal. Those wires play
important role in position adjustment of the sensor: they allow to set it
with high accuracy and relatively good stability.
This sensor is able to detect object from 0.5" to 2" depending
on its reflexivity. |
TeamUR the First's sensor
Simple sensor assembled. |
This specific set has been purchased for
test purposes from Acroname which provides the specification
of IS471F.
The main problem we encountered was that the light beam was not focused on
the distant object. |
The sensor is signaling an object not detected |
We used a piece of tubing on the IR LED to eliminate unwanted
beam dissipation .
The detector in this shape was able to sense a finger from 2-3
inches. The green LED shows: no obstacle. |
The sensitivity of the above sensor was sufficient to detect a finger
from 2 inches. For our small robot it is sufficient. |
