Author Topic: INFRARED SENSORS!!  (Read 1352 times)

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Offline patwariTopic starter

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« on: June 24, 2008, 11:26:43 PM »
Hey,I am pretty new to electronics.
I plan to make a line follower with obstacle avoidance for which I would need an infrared emitter detector..
This is what I already know..The ir emits rays that strike an obsatcle and the reflected rays fall upon the detector which is a photodiode.considering the fact that a photodiode works on reverse bias where breakdown occurs and the reverse current is generated.(electric signal)
Now what I want to know is what  1> happens to this reflected ray..???  2>What does a photodiode do to it???
 3>How does an ADC interpret this  signal???
Does it have any specific voltage like (say 1.7volts or something)??

Offline BANE

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« Reply #1 on: June 26, 2008, 10:20:43 AM »

Offline paulstreats

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« Reply #2 on: June 26, 2008, 05:25:34 PM »
1) The semiconductor material in the photodiode changes resistance depending on the amount of light falling on it. IR photodiodes have a gas filter that only allows infrared light to shine on the semiconductor material. So the more infrared light there is the less (or more depending on type of material) resistance is produced by the photodiode. (In your case imagine it as being a photoresistor or a light dependant resistor that reacts only to infrared light)

2)The photodiode doesnt do anything at all to the light rays, its the light rays that alter the photodiode (This is basically the same question as the one above)

3) The output of the photodiode should produce a changing current (depending on the level of the infrared light shining on it. So a lot of light will let a lot of current pass and a little bit of light will let a little bit of current pass). To use this with an ADC port you will need to use a voltage divider. This is just a plain old resistor connected from the output of the photodiode to the ground (GND). The connection to the adc port should come from the connection between the photodiode and  resistor (The value of the resistor will affect the high and low voltage levels aswell as the ratio of change so youll have to test to see which one is best for your application). This will make the voltage alter accordingly with the current (so a lot of light now becomes a lot of voltage probably 5V and a little it of light will produce near 0V). The ADC port can now recognise the changes in voltage and give you a reading in software to do something with.

Some people dont even other with an adc port, if you choose the resistor correctly then you can get it to register one extremity to another and just produce a high or low signal for a normal i/o port. (I always use the ADC method though since you can extract more data with differing values so if you know that a lue tale produces 1 value then the next time that value occurs the root must be on something blue. You dont only have to use the for following a black line on a white background)


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