RE: Nigel's IR transmitter - some questions from a begin ner about to bu ild one.

["Ian" <I.Bird@xxxxxxx>]

You're right. I turned the IR LED round and hey presto it all worked as
designed. The next task is to etch the board and build it and see if it
works. All the LED's are alive and well which only leaves me one capacitor
down on the weekends fun. Oh ye, the bit that fooled me was the long leg
was
negative (I think). I also learnt that you can test LED's with a diode
tester and find this out.

Ian

-----Original Message-----
From: Robert Chasmer [mailto:robert.chasmer@xxxxxxx]
Sent: 13 November 2000 18:01
To: 'ukha_d@xxxxxxx'
Subject: RE: [ukha_d] Nigel's IR transmitter - some questions from a
begin ner about to bu ild one.


Ian Wrote:
> The visible LED flashes as it should but no IR signal out. In a fit of
> complete madness I then tried a total of 5 out of 6 IR LEDs and none
of
> them worked. About this time I wondered if I had the LED connected the
> correct way round. My guess (and Nigels, the circuit creator) at the
> moment is that I have toasted all but one IR LED. Time to do some safe
> testing to find the good  one and ascertain its polarity. I did some
> research this morning and it seems it is opposite to the visual LED so
> woops, Lesson 2: insert components the correct way round and check,
> check and treble check!

When I built the ciruit I used just visible LED's, after testing I swapped
in the IR LED.

Most LED's, and the IR LED's I had, have one leg shorter than the other.
The shorter leg should go towards the (-) negative, the longer leg towards
the (+) positive.  Some round LED's also have a flatter bit on one edge
which also point towards the negaative.  Once the circuit works ok with the
visable LED's it should just be a case of swapping it with an IR one.  I
also had to make sure the IR LED actually pointed towards my TV, or HIFI to
get them to recieve the IR commands. [Disclaimer: All of this could be
complete Tosh!]

Surely if your using an inline resistor you unlikely to have fried the
LED's.  I thought diodes were meant to prevent current flowing in the wrong
direction, there not fuses?

I've only managed to fry a 555 timer so far.  Ahh the smell of burning
electronic components!


Rob
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