Re: Urgent - Time to kill, want to build IR Extender

[Nigel Orr <nigel@xxxxxxx>]

At 18:33 30/10/00 +0000, you wrote:
>few questions (all of you electronics experts can feel free to laugh at
my
>stupidity!).

I won't be laughing, at least not until I correct the schematic with that
stupid error of missing out the +12V connection :-)

>First off, the 555 timer has an indentation on the top, does this
indicate
>pin 8, also are pin numbers ordered as per Nigel's diagram, if not what
is
>the sequence.

ICs usually look like

8  7  6  5

i  i  i  i

o
i  i  i  i

1  2  3  4

Where i are pins,  is a bar sometimes marked at one end, and o is a dot or
dent which marks pin 1.  That's fairly consistent for almost all ICs.  The
'o' at pin 4 on the schematic represents an inverted input, which means
that it is reset when the input is low, it's got nothing to do with the
package markings.  Sometimes the same thing would be shown as an R with a
bar over the top of the letter- just depends on the schematic drawing
package.

>Second, the LED's, I know that the shortest leg is the cathode, does
that
>mean the other leg is the one to connect to the +12V.

Probably.  Some LEDs are the other way round, there's no particularly
common standard, if you can see inside, it looks a bit like a wire going
into a 'cup'.  The 'cup' is usually the cathode (I think, I usually just
test them with a battery!).

Best way to check is to put an ordinary visible LED in series, with a 9V
battery and a 1k resistor, then swap their direction round until the
visible one lights- at that point, both anodes are towards the +
connection.  If you have a CCD camera or camcorder, you don't need the
visible LED, as you can 'see' when the IR one is on.

>Third, the transistors, how do I know which leg is which. I have
assumed the
>diagram shows the plan view of the transistor, but there is a little
tag by
>one leg which I have assumed is number three on the diagram, is this
correct
>?

Usually, though again not definitely, emitter (1 on the diagram) is nearest
to the tag.  If you have a multimeter with a diode test setting, it's
possible to check the other pins, let me know if you want to know how.  The
diagram is just a standard schematic layout, it might not correspond to the
physical layout of the transistor you have.

The Maplin catalogue usually has package pinouts for transistors, check
whether it is shown as 'view from above' or 'view from below'.  Where the
transistor is listed in the catalogue, it will say package type, something
like 'TO92', at the start of the transistors section there is usually a
page showing all the different packages and pins.

Pin 3 on my diagram is collector (C), 2 is base (B), 1 is emitter (E).  If
that doesn't make sense, send me an email with the details of the
transistor you have and I'll try to give more specific directions.

>Finally, is there any way I can test the transmitter without a receiver
and
>when I get a receiver (hopefully from Keith), where does that connect
to the
>transmitter ?

There are 2 lines sticking out to the left of the diagram, with some stuff
about 'input' on them.  The lower one connects to the receiver's 0V
connection, the other to the receivers output connection.  The receiver's
3rd pin needs to be connected to +5V +/- 0.25V.

The only way to test before the receiver arrives is using an oscilloscope,
a multimeter with a frequency meter, or a camcorder/camera.  If you have
any of those, let me know and I'll tell you what you can use it for.

>I am sorry for these really basic questions, but this is my first ever
>circuit and I would rather it didn't go bang as soon as I connect the
power.

Where's the fun in that   :-)  ?  I'm happy to try to help you get it
sorted, feel free to email me directly if there are any more questions-
unless others on the list want to see more gory details?

Nigel


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