Nigel's IR Transmitter - a beginners tale (longish)

["Graham Howe" <graham@xxxxxxx>]

OK (almost *) everything is now working so here as promised are the details
of my experience. First of all a very big thank you to Nigel himself for
providing the circuit and a large amount of support here and in private
emails. Also thanks to Keith for supplying the elusive TSOP 1838's (I may
well be ordering some more in the near future).

To start with here is a list of all the components that I have used from
Maplin's (note that I did buy others, but this is the final selection for
the completed prototype). All prices are rounded up to the nearest penny.

Maplin # - Description - Price
QH66 - 555N Timer - £0.25
QB31 - BC107 Transistor - £0.25 (x 2)
WW76 - 47uF Capacitor - £1.27 (there must be a cheaper alternative here but
I don't know it)
RA44 - 0.01uF Capacitor - £0.16
WX57 - 120pF Capacitor - £0.11
CY88 - Infra Red LED - £0.67
NP04 - Red LED - £0.09
M10K - 10K Resistor - £0.06 (x 2)
M150K - 150K Resistor - £0.06
M680R - 680R Resistor - £0.06
M2K7 - 2.7K Resistor - £0.06 (x 2)
M100R - 100R Resistor - £0.06
Total for the transmitter components £3.47

You will also need a 12V supply, I used Maplin code UD02 (£10.20) but of
course this will be replaced by an output from Comfort once that is
installed. For each receiver you need one TSOP 1838 (not available from
Maplin), one 5V1 Zener diode (QH07 £0.05) and one 2K Resistor (M2K -
£0.06).
You will also need some wire for making connections, I just got some red
and
black bell wire (BL92 and BL85 - £0.59 each).

Next to consider is mounting boards, I would not even consider trying to
make the transmitter without a Solderless Breadboard and would suggest it
is
useful to have another one for prototyping the receiver as well. I bought
two BZ14 - £6.80 which have plenty of rows and columns and have 5 screw
down
terminals. I choose these to give easy and secure connection of the CAT5 I
was using for connecting the receiver to the transmitter. It would be OK to
buy the significantly cheaper boards if you are not going to be walking
around the house with the receiver pulling several meters of CAT5 behind it
! I have now soldered up a receiver on a JP46 Stripboard - £0.59, this was
the smallest board I could find and would do for at least 4 receiver
modules
(by the way, what is the easiest way to cut strip boards ?). I have not yet
mounted the transmitter on a soldered board, but I have bought a JP49 -
£1.69, for this purpose. I also bought a tool for cutting tracks (FL25 -
£5.52) as the circuit is much more complex, but I guess that there are
other
alternatives here (if I had a Dremel I'm sure there would be a suitable
attachment).

Talking of tools, here is a list of what I used:
Small long nosed pliers for pushing components and wires into the
solderless
breadboard.
Wire snips for cutting wires (teeth for stripping them !)
Soldering iron and solder
Multimeter for checking resistor values (learning the colour codes would
have been cheaper but take much longer). Also used for checking voltages
and
to ensure that I had not joined two tracks on the breadboard with my
distinctly amateur soldering.

Problems/lessons learnt
The initial problems I had were due to a fundamental lack of knowledge of
electronic components. For example knowing which pin was which with the
timer chip, knowing which leg was which on the transistors and knowing
which
way round the LEDs were supposed to go. When you buy the components from
Maplins there are no instructions or diagrams and their web site is also
very lacking in this respect. However RS website (http://rswww.com) does
have a great deal of technical information if you register. So I actually
managed to get diagrams for the majority of the components from this site.

Of course I also had some problems with the circuit diagram that does have
two errors (though Nigel is sorting them out). The first is that there must
be a link from pin 8 to the 12V line, the second is that the visible LED
(D1) is connected to the 12V when it should be connected to the 0V
(ensuring
that it is the right way round).

The other difficulty I had was in converting the circuit diagram to an
actual circuit on the board. I started trying to make the components sit on
the board in roughly the same positions as they are on the diagram, but
this
simply does not work because the central chip does not have it's pins
ordered in the way they are on the diagram. So after ripping everything off
the board and starting again, I placed the chip in the middle then added
one
component at a time, starting at the centre of the diagram and spiralling
out. This means that the physical circuit does not look like the diagram.
For example on the diagram there are a whole string of components between
pin 5 and pins 6,7 and 8 and it still looks reasonably neat, however when
you consider that pin 5 is on the same side of the chip as 6,7 and 8 then
the physical layout looks very different. When I finally build the soldered
circuit I will take some pictures and put them up on my site.

* Why almost ?
Well at some point during my prototyping of the circuit I must have blown
the IR LED (CY88) because it is completely dead, so I need to go and buy
another one. However I did have a spare visible LED and by putting that in
the circuit in place of the IR LED I can see it flashing in response to IR
commands being fired at the receiver. So my conclusion is that the circuit
is working and that when I replace the IR LED I will get remote wired
transmission of IR commands.

Next Steps
Once the prototype is working I will be attaching RJ45 plugs to the
receiver
and transmitter and trying them through my current house network. I say
current network as I will be expanding my CAT5 wiring to 88 ports in the
coming weeks with the intention of using structured wiring for LAN, Phone,
A/V (with the KATV modules), Security (Comfort Keypads will use shielded 8
core, detectors will use CAT5) and IR distribution (to and from HomeVision
primarily). The intention is that any port can be mapped to anything in a
wiring cabinet using patch panels and that any piece of equipment
(computer,
printer, phone, TV, A/V source, PIR, smoke detector, temperature detector,
IR receiver, IR transmitter) can be plugged in anywhere using a normal RJ45
equiped fly lead. I will have all wiring terminating in the home office
where the LAN Server, HA Computer, HomeVision, Comfort, Router and Printers
and Scanners will be located.

I hope all this is useful to others, I am planning to post all progress on
my transition to a 'Smart Home' on the web as I go along.

Regards

Graham


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