I was inspired by the German site and by Roger's work so yesterday at work
while waiting for some E. coli to grow, I tried my hand a making a LED dash
light.

materials:

red LED from bike light. Unsoldered from little board, which of course meant
it only had very short "legs". Checked out to be approx. 1.8 V and a narrow
beam spread (20 degrees?). "Flattened" area at base of LED indicates the
negative post.

resistor - 470 - 500 ohm (calculation/estimation based on a dash voltage of
10V and a LED voltage of 1.8)

dash light bulb holder.

some 22 gauge telfon insulated tinned copper wire (scraps at hand)

heat shrink tubing.

Method (made up as I went along):

drilled 1/16" hole in base of bulb holder. Soldered 1" lengths of wire to
the legs of the LED. shrunk small lengths of heat shrink over the solder
joints. Cut one of the lengths of wire back to aprox 1/4" and removed
insulation. Tinned/soldered the exposed wire to make solid. Bent that back
upon itself to make a tight "V".

The other wire is fed down through the bulb holder and out the drilled hole,
The LED is pressed into the holder with the bent wire making contact with
one of the internal bulb holder contact. The LED is a good fit and the bulb
holder itself "stretches" a little to hold it in tight. I marked with a felt
pen the side of the bulb holder that the LED was making contact with the
internal contacts.

The wire sticking out of the base was trimmed a little and leg (trimmed
also) of the resistor soldered to it. A very short length of wire was
soldered to the other leg of the resistor.

The free end of the short length of wire was soldered to the "topside" ie
the side that does not come in contact with the circuit foil. This is a
tricky part, you'll see how to solder it when/if you do it!

A bit of heat shrink over the resistor and wires and its done!

One has a 50% percent chance of getting it right when you twist it into the
circuit foil, I don't know if these LEDs "pop" if full voltage is applied
"backwards" so I inserted into foil with dash light rheostat turned way
down.

Well it works, but as Roger found too, the beam is quite narrow and only
illuminates the top half of the gauge. The little reflector assembly might
be modified (foil inside?) but better to have a wider beam spread LED.

Inserted into the centre position, that is the bulb that lights up the idiot
lights, the LED illuminates all of the icons but not evenly.

The LED does dim with the rheostat, but does not go out at the
lowest/dimmest setting.

But I think it was a worthwhile exercise, now I'll go get a range of LEDs
and experiment further.

Alistair

--
'82 Westy -> diesel converted to gas in '94
albell@uvic.ca
http://members.shaw.ca/albell