Subject:
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Spybot studies: photoelectric eye
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Newsgroups:
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lugnet.robotics.spybotics
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Date:
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Thu, 6 Nov 2003 16:17:20 GMT
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Viewed:
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6106 times
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I've started a new project to explore the Spybot's capabilities, (now the John
Hansen has given me access to them ;). I plan to undertake s series of "studies"
which each explore a single feature or function. I'll post then as I go.
This first one doesn't use any of the new Spybot API. Nor is this really special,
and I'm sure someone has done it before.
All you need to compile it in BricxCC is set your brick to Spybot.
NQC code for photo_eye3.nqc follows:
/* Photo eye
Use the Spybot LED and light sensor as a photoelectric eye.
Physical configuration: fiber-optic cables are affixed to the light sensor
and LED, and the ends of the cables are pointed directly at each other at
a distance of one to 14 studs. (I didn't test beyond 14 studs.)
I've posted an image at
http://www.brickshelf.com/gallery/ALittleSlow/Robotics/SpybotStudies/PhotoEye/photo_eye.jpg
All relevant files are posted at
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=62324
*/
#define TONE_LOW 220
#define TONE_HIGH 880
int photo_threshold;
task main()
{
calibrate();
start detect;
// wait for bumper to end program
while (! SENSOR_1) {
Wait(10);
}
SetLight(LIGHT_OFF);
StopAllTasks();
}
/* calibrate photo-eye
*
* This is a very simple calibration algorithm which sets the detection
* threshold at half of the light which it receives from the LED.
*
* With the LED off, take a light reading.
* Then turn the LED on and take another reading. The difference is the
* amount of light contributed by the LED. Set the threshold at half that,
* meaning if we can see less than half of the LED's light, something must
* be obstructing it.
*/
void calibrate()
{
SetLight(LIGHT_OFF);
// default mode is SENSOR_MODE_PERCENT, I think.
// default (and only possible) type is SENSOR_TYPE_LIGHT
SetSensorMode(SENSOR_2, SENSOR_MODE_RAW);
int photo_high = SENSOR_2;
SetLight(LIGHT_ON);
Wait(1); // make sure the light is fully bright
int photo_low = SENSOR_2;
photo_threshold = (photo_high - photo_low) / 2;
}
/*
* Task detect
*
* Plays a tone when it detects an interruption of the LED beam.
* To provide some additional feedback,
* the tone's frequency corresponds to the value of SENSOR_2. In a real
* application, you might set a global flag instead of playing a tone.
*
* To save power, the LED is on only once every 110 ms or so.
* Adjust the Wait() time to suit your precision or power
* requirements.
*/
task detect()
{
int photo_ambient;
while (true) {
photo_ambient = SENSOR_2;
SetLight(LIGHT_ON);
Wait(1); // wait for the light to get fully bright
if (photo_ambient - SENSOR_2 < photo_threshold) {
PlayTone(SENSOR_2, 10);
}
SetLight(LIGHT_OFF);
Wait(10);
}
}
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Message has 1 Reply:
 | | Re: Spybot studies: photoelectric eye
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| (...) I think this is fantastic, Brian. I look forward to seeing future posts on the results of your studies. I am working with Dave Baum to incorporate the new Spybot API features into the official NQC API. One aspect of that involves documentation (...) (21 years ago, 6-Nov-03, to lugnet.robotics.spybotics)
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