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IR transmission

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Captain_Tuna:
Hi guys :)

i want to ask you a few questions about IR transmission. (haven't found answers to those in the tutorials or with the search tool above)
what i am trying to do is something like this guy has already done: http://www.lasertagparts.com/mtformat.htm
he basically has a very precise protocol, each binary series corresponds to a specific action. I don't really know how to achieve something like this though. I believe, but i'm not sure, that for the transmission of binary signals you can simply use PAUSEs and HIGH <IR_led_pin>.
 example:
 i want to transmit 110011.
 could i write something like this on my microcontroller? :
high 1 (suppose 1 is the ir led pin)
pause 20
low 1
pause 20
high 1
pause 20
low 1

------

also i do not really know how these signals can be read by an IR receiver. As far is it is a single signal it shouldn't be too hard (as for range finders for example, or the thing shown in the IR tutorial on this site) but when it comes to multiple, very close to each other signals i don't know how to proceed

could you help?
:)

izua:
well, first you will need a fast frequency (carrier) which will pe used to modulate your message.
due to all the infrared sources around us, you can't simply hook a led to an UART pin and expect the message to correctly end up at the decoder.

then you'll probably want a protocol, maybe with addresses, maybe with a checksum.

Captain_Tuna:
ok, i'll start by documenting myself on fast frequency carriers. But what about the receiver? does it also need something?

Captain_Tuna:
ok guys! this is what i found so far: (i'll post them here so someone else can also benefit from these infromations)

http://www.rentron.com/Infrared_Communication.htm
http://www.scienceprog.com/ir-remote-control-signal-receiver-using-avr-microcontroller/

these are not complete walkthroughs or anything similar, but i think they are a good point to start from. I still need some time to understand how the whole thing works as i just go into robotics/electronics.

As for the receiver: i found that TSOP17xx have built in demodulators, that sounds great, even if i still need some more knowledge on how to make my bot (microcontroller , that is) interact with these (even if demodulated) signals.

izua:
I wrote a small tutorial on decoding RC5 from remote controls with a TSOP sensor. Check it out on my website.

Basically, with a TSOP you get a signal you can feed your UART. But noise may still appear. From the other end, you can get an astable oscillator a tuned frequency, when the TX pins goes high, it enables this oscillator, thus creating modulated light. When the TX goes low, oscillator is disabled. By this method you effectively superimpose the carrier with the original data.

you can also get a pwm pin at your frequency and feed it to an AND gate, along with your TX. this way, you don't have to build an oscillator, and the signal will be more precise.

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