Re: IR detector system, biasing of photo diode

On 31/10/2024 2:09 am, john larkin wrote:

On Wed, 30 Oct 2024 09:45:42 +0100, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:
 

On 30-10-2024 00:31, john larkin wrote:

On Wed, 30 Oct 2024 00:02:34 +0100, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:
>

On 29-10-2024 18:26, john larkin wrote:

On Tue, 29 Oct 2024 17:02:02 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>

john larkin <jl@glen--canyon.com> wrote:

On Mon, 28 Oct 2024 20:31:14 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>

On 2024-10-28 17:10, john larkin wrote:

On Mon, 28 Oct 2024 15:49:30 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>

On 2024-10-27 08:26, Klaus Vestergaard Kragelund wrote:

On 27-10-2024 03:26, john larkin wrote:

On Sun, 27 Oct 2024 02:19:14 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote:

<snip>

The credit card experiment is morally equivalent to using two square
tubes stuck together.

He meant conceptually equivalent.  Components don't have morals.

Now mount two LEDS, red and green, to the common
wall, at the back of the tubes. Shine that at a wall. It should
project two fuzzy squares, red and green, barely overlapping, with a
fuzzy orange stripe between them.

It will look orange to a human being because our optical frequency discrimination system sucks.

That could actually be two IR LEDs modulated at different frequencies,
or two photodiodes.
 TV remotes work very well, so I wouldn't expect s/n problems with the
emitter and detector staring at one another a few feet apart.

TV remotes are doing a rather different job.

Use multiple LEDs stacked vertically along both sides of that back
wall (which should actually be a PCB) and apply a lot of square-wave
current.

Why square wave? It's just the sum of the sine wave fundamental, and all the odd harmonics of that fundamental. A triangular wave is just as easy to generate, and while it has the same harmonics,the amplitudes drop off as the square of the frequency. Generating a sine wave isn't all that difficult.

We like the Osram right-angle surface-mount LEDs, but there are lots
of parts like that around.

Scarcely the right part for this particular job.
--
Bill Sloman, Sydney