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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: IR detector system, biasing of photo diode
Date: Thu, 31 Oct 2024 14:17:57 +1100
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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