I enjoy reading all the comments but apologize that
there are so many I can’t answer individually. I’m delighted that my
new videos have been so enthusiastically received, which is reflected in
the majority of the comments. The videos aren’t perfect though so below
each video I’ve compiled the comments about things I omitted or people
thought were misleading. A few comments added wonderful additional
information so I’ve included them as well.
Quite a few people criticised my sum for working out the
value of the resistor to put in series with an LED. To get the maximum
brightness, the forward voltage of the LED (part of the spec) can be
deducted from the supply voltage. Personally I prefer not to run LEDs to
close to their max as I have had many fail over the years, mainly because
of overheating. Also their brightness does not visibly diminish dropping
the power by 20%. (in fact one person wrote that hepowers his daughter's
12v dolls house LEDs from nine volt batteries). However the criticism is very valid when the power
voltage not much higher than the LED voltage. If I had used a 6v supply
for my 3.3v power LED, my rough sum would have resulted in a resistance
twice as high.
Apparently its not strictly true that LEDs can’t be
harmed by connecting them the wrong way round. High reverse voltages and
even low voltages on some newer surface mount LEDs can fry them.
Donald Sayers reminded me that a single flashing LED can
be used to flash a whole chain of LEDs wired in series. I wish I had
included this. Even better, the wonderful Evil Mad Scientists have a
simple circuit using a flickering tealight LED as the base of a transistor
circuit to make a high power flickering circuit. I used this on the sign
at the top of my i-Zombie machine. (https://www.evilmadscientist.com/2011/does-this-led-sound-funny-to-you/)
Mark Harriss had managed to see light with a wire touching
36grit silicon carbide abrasive. It required about 1amp and 20 volts, and
produced a variety of different colours.
Several people wrote to explain the warm LED filament
household lights. They are strips of tiny surface mount LEDs covered by
silicone and phosphors. They require about 70vdc which why I hadn’t
managed to get them to light up! One person added that they were invented
in China, before being copied by Philips and GE. Also that the strips have
four blue LEDs and one red one in series, with the phosphors blending them
to the warm yellow.
Vincent Sullivan wrote that the numbering system used for
surface mount LEDs referring to their size in mm is also used for other
components, particularly coin cells. So for example a 2030 cell is 20mm
diameter and 3 mm thick.
Gordon Slater uses a 4 inch bit of wood with a blunted
sewing machine needle on the end to rest (or lightly clamp) on surface
mount LEDs while soldering. Extra flux was another suggestion.
Electra Flarefire wrote that the clear coating of
waterproof LEDs strips is clear PVC, not silicone. Of course, this is why
they are completely clear, not translucent. It also explains my experience
of the coating becoming stiffer and brittle with age as the plasticisers
in the PVC evaporate over time. Useful for school projects, 12v strips
will run from 9 volt batteries without too much loss of brightness.
Tom Z added a great fact about the bonkers over-engineering of some BMW
headlights which use blue lasers aimed at phosphors to create the sharp
focused beam.
Plons0nard suggests Bascom Basic Compiler for programming arduinos and
particularly addressable LEDs as it has a specific 'rainbow' subroutine.
Another suggestion was 'Circuit Python'.
Quite few people had different ways of memorising the polarity of LEDs.
My favourite was that the flat on the side is the shape of a minus sign.
