I/R transmitter Reciever

Hi. Absolutely new to Robotics. Have a chassis with tracked drive. Am thinking first of developing some system of obstacle avoidance. In this
connection, using a relatively cheap system of I/R Transmitter and I/R Phototransistor, I need to know if the I/R beam from the Transmitter will bounce or reflect from obstacles, so enabling the beam to be detected by, say, a Phototransistor seated inside a conical reflector. What would be the state of this reflectance from soft surfaces, curtains, furniture, etc, compared to hard reflective surfaces? Is this a viable scheme for the purpose intended? Love to hear from someone who has investigated this mode. Thanks. Walt.
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Hi Walt,
IR Detectors I’ve been doing some IR tests recently and think modulated IR and IR detectors will give you better range for obstacle avoidance. Panasonic (PNA46xx) and Sharp (GP1UDxxxx) are probably the best IR Detectors. Vishay has better range but the AGC causes problems. I glue short tubes on the detectors to prevent any stray IR light from affecting it.
For the IR LED You can use a 555 or a microcontroller to generate the modulation frequency (30kHz to 56kHz depending in the detector). I use a microcontroller a 2.2k ohm current limiting resister and get 4-10 inch range, 4 inches for a soft black target surface, 10 inches for a hard white. If you use a 500 ohm current limiting resister and the light will bounce off everything in the room.
Jay

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Hi there Jay. Thanks for the interesting on IR obstacle avoidance. Do you have any idea where I can source creditable circuits for this type of setup? Which of the two did you personally find most useful Jay? I would like to begin building the modulation circuit straight away so that I can evaluate the system. Sadly the Chassis I wanted turned out to not have track mobility, so that idea was scuppered. I am now looking around for a fairly cheap tracked vehicle. Toy Farm Tractor or Army Tank that I can strip for the chassis and motor assembly. Tut! Best laid plans and all that. Okay, I shall set about finding some info on the two IR's that you mentioned. Data sheets or something. Cheers Jay. Walt.

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Hi Walt,
Personally I like the Panasonic detectors.
If you do a Google search for 555 and "40khz" You'll find plenty of modulator circuits.
The detectors come in different frequencies from 30kHz to 56 kHz. (TV Remotes are usually 38 or 40 kHz) They contain a demodulator and filter and usually output a ground signal then they detect a modulated signal.
BRAINS Were you going to use a microcontroller or design the controls with discrete logic?
Jay

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Hi Jay. Strated building the circuits for an I/R Detector and an I/R Transmitter. Building seperate units so that I can experiment with limiting the beam travel as it would be impractical for the beam to be more than, say, six inches. In fact I would prefer a little shorter distance. I do need a source on info on limiting the travel of an I/R Beam, but where do I find it? Do I increase the resistance, or do I insert I/R limiting filters in front of the lense? I wish I knew.
I have had great success finding a nice R/C controlled Tank with super tracks. It has a R/C Reciever and two servo's installed wich I shall remove. I can find a use for them with the Transmitter included. So things are sure looking up for me at this end. Now what shall I call it? Hmmm! Have to think about that. Cheers Jay. Walt

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Hi Walt,
There are three techniques to reduce range that come to mind. Increasing the value of the IR LED current limiting resister, shifting the modulation frequency and reducing duty cycle. ( the percentage on / off times. The latter two can be done under software control while the robot is running.
Increasing the current limiting resister to 22 k will result in a range of 2 inches, 2.2k gives a range of 12 inches. I'm using an AMD microcontroller on 5 Volts and a flat / white target. The range is about half with a black target.
Here's an interesting article on frequency shifting. http://www.parallax.com/images/customer_apps/willp/Robot%20Wall%20Sensors.pd f
I've experimented with duty cycle and find little difference in range between 50 % and 10 %. I plan to reprogram my tester and try below 10 %. Next I'll experiment with the Frequency shift.
I'm currently testing an analog IR solution for line tracking, two photodiodes and an IR LED, but haven't got the program running yet. Analog IR has some advantages and I'm exploring those.
Jay

chassis
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www.polydroids.com has tracked bases and digitally controlled 38KHz IR proximity sensors. If you use two of these you could probably make them communicate since one pin can enable/disable the transmitter (at a low frequency say 600 Hz or so). You would need the output of the other one to do some sort of tone-decode (using an LM567 for example) on this to get your on/off out.
-Kip

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