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'[PIC]: How to implement a Infrared communications'
2002\06\30@173018 by Andrew Errington

You could directly drive the IR LED, but typically you will want to use a modulated IR waveform to avoid interference from lights and daylight.  A simple example is shown in one of the original Basic Stamp application notes.  There is a link to it here:

(I don't know why it's there, but that's where Google took me)

Basically your serial comms line gates the 40KHz waveform generated by the 555 on and off, or you could generate the 40KHz waveform in software in the PIC instead.  The GP1U52X shown is one of a number of different IR receiver/demodulators that can detect the 40KHz (or 38KHz) waveform and produce clean TTL output.

Be careful with the sense of your signals.  RS232 idle is a logical '1', but you probably want that to be represented by a physical '0' state, otherwise when the link is idle the LED will be on and the system will be consuming power.

I have played with this and had 9600bd comms across a room (about 4m) with good results.  You should probably add some error checking codes in your data stream so that the receiver can determine that the data was received correctly.

Hope this helps,


> Hello everyone,
>         I need to comunicate an 16F627 with another 16F627, using infrared
> technology (maybe or not IRDA compatible)
>         I was planning to use MAX3100 and/or MAX3120, but are to costly
for the
> project.
>         As a cheaper way of doing this, can I directly connect an infrared
led to
> TX and an infrared detector to RX on both devices ??
>         Is it right ? Another way of doing so ?
>       Thanks, Gabriel.-

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2002\06\30@220806 by Jinx

face picon face

In addition to what Andrew has said, the circuit I always use

IMHO transistors like the 2N2222 (as used in the Stamp
example above) are crap for IR transmission. They can't
switch high LED current fast or cleanly enough. ZTX types
are far far better. If possible you could add a reflector with
the LED(s) pointing backwards into the reflector. Also, if
you can get your hands on one from a dead VCR or TCV,
those sealed can receivers are excellent for response at
distance and for wide-angle coverage (eg wall-bouncing).
The IS1U60-types are OK within a fairly narrow beam.
Immunity to ambient can be improved by adding an extra
filter (eg exposed film, perhaps a blank frame from a roll
of negatives - dark dark purple) and making the receiver
pick up the beam through a shortish tube

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2002\06\30@222301 by Russell McMahon

Re transformerless offline power supply.


As well as the "always use an isolating transformer ..." warning it would be
worth adding, right next to the circuit, a warning along the lines -

WARNING - In transformerless circuits such as this one ALL components
including the equipment powered should be treated as being at full mains
voltage at all times. While the output circuit is designed to be nominally
at earth potential, changes in the manner of connection or incorrectly wired
mains power outlets may result in the whole circuit being "live". Failure to
treat the circuit as live at all times may result in death.

       Russell McMahon

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2002\06\30@233658 by Jinx

face picon face
> As well as the "always use an isolating transformer ..." warning it
> would be worth adding, right next to the circuit, a warning along
> the lines -

Good idea - tis done

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