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From: David Chen <nospam-dcchen@pacbell.net-nospam>
X-Real-Life-Name: David Chen
Subject: IR Port as Proximity detector.
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Date: Fri, 8 Jan 1999 06:15:11 GMT
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Someone (Can't remember who, so unfortunately unable to give credit for
the idea appropriately) posted the fact that the IR port used as a
emitter coupled with the Light Sensor unit as the reciever can be used
as a IR proximity sensor.

Seemed like a good idea.  Had not heard of it done before on this news
group.  Thought I'd give it a try.

NQC code as follows for a test program called Ping.

/*
 * Ping
 * ===========
 * Reads light level into level, transmitts it out via SendMessage.
 *
 * Mapping:
 *   OUT_A: empty
 *   OUT_B: empty
 *   OUT_C: empty
 *    IN_1: empty
 *    IN_2: light sensor
 *    IN_3: empty
 *
 */

#define THRESHOLD 70

int level;

task Ping

{
  while(true)
  {
    level = Input(1);
    if(level > THRESHOLD)
      PlaySound(1);
    SendMessage(level);
  }
}

task main
{
  // Set up the sensors
  Sensor(IN_2,IN_CFG(STYPE_LIGHT, SMODE_PERCENT));

  // Start Tasks
  start Ping;
}

This has the RCX sending infrared pulses out constantly, if the
reflected pulse is > THRESHOLD (arbitrary values, see below), then it
beeps.

THRESHOLD values I have found to cause beeps when Light Sensor is within
the following distances to a wall painted white (flat wall indoor
paint).  Your milage may vary depending on ambient light.

Threshold:	75	70	60	55-

Range:		6"	4"	3"	Triggers constantly at with the
					ambient light.

Perhaps a routine to adjust for Threshold = average ambient level + 20
would work?

Whoever's idea this was, it was a brilliant one.  Now you have an IR
object detector/range detector to use along with your 2 touch sensors.
I can now use the touch sensors for side collision detection and IR
sensor for front.

Next, use a 3rd motor for side to side scanning of objects...

Dave Chen