using a LED as a light sensor

Hi,

Here is an idea about using a LED as a light sensor, to dim a 7-segments LED display :

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Questions & comments are welcome !

Thanks,

Bruno

Reply to
BrunoG
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I've heard of doing this before, and I think it's one of those really neat ways of doing something. You don't have to have a light sensor spoil the front panel of your project....if you're into the visual appearance as much as I am.

Reply to
hondgm

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I like the idea of using an LED to control its own brightness, relative to ambient light. Drive it with an output PWM (that does not ever go to 100%), through a current limit resistor. During the off time, measure the LED's generated voltage by switching the output to an analog input. The current limit resistor between output and LED has little effect on the analog voltage measurement. The generated voltage will be proportional to the log of intensity.

Reply to
John Popelish

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that idea also works with irradiation detection. we use a cluster of LEDS in a camber to detect small leakage. we also use a couple for large leakage. we use a non silicone type emitter into an LED, the idea is if excess IR gets near the LED it burns it out and shuts down the system. also at the same time, if we detect a flicker of light level we can thus determine an arc took place. and yes, we do have to replace it when this happens. but this only happens like once every 10 years or so. in the vessel(FS6 gas filled) we do use a 12 level photo multiplier because we need to know when the slightest hint of photon is present in the vessel. this normally indicates that we mite have a vacuum problem, LEDS and even Silicone photo detectors are not sensitive enough for that application. (at least they wasn't back when it was designed).

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Reply to
Jamie

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Reply to
John Fields

Mistubishi Electric Research Labs published a paper describing using a led for bidirectional communications.

Do a google search for "TR2003-35".

Reply to
dmm

... snip ...

We used to criminally overvoltage selected photomultipliers for coincidence detectors, which needed to detect a single particle hitting the crystal, after which hopefully at least one photon got collected on the photo-cathode. We used in the order of 2kV on tubes rated at 1 kV. You turned up the voltage, and if they didn't start generating violent noise you kept them. The others went back to the stockroom. I seem to remember a 1P21.

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Reply to
CBFalconer

Too many excmamation points!

For a more serious challenge, use the live 7-seg display itself as the ambient light sensor. No ADC allowed. For advanced credit, no extra parts allowed at all, just firmware.

John

Reply to
John Larkin

Are LED's more efficient as light sensors than so called photo diodes?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Is that for continuous adjustment or just Lo/Hi operation thresholding?

Reply to
Fred Bloggs

"Jim Thompson" a écrit dans le message de news: snipped-for-privacy@4ax.com...

Hi,

Surely not, I just present an odd way to use a common LED.

Thanks,

Bruno

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Reply to
BrunoG

I suspect it is SF6:

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Jon

Reply to
Jonathan Kirwan

"Fred Bloggs" a écrit dans le message de news: snipped-for-privacy@nospam.com...

Hi,

in this example this is just an Hi/Lo operation thresholding. for continuous adjustement, an analog extra circuitry would be needed.

Thanks,

Bruno

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Reply to
BrunoG

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Reply to
John Fields

it dans=20

Keep in mind that an LED is good at converting to DC, only a range of=20 wavelengths that are shorter than the emitted wavelength. A red LED=20 does not respond much to red light, but produces a fair signals when=20 exposed to green and blue light, etc. Blue LEDs make pretty nice UV=20 detectors that ignore visible light..

Reply to
John Popelish

"John Larkin" a écrit dans le message de news: snipped-for-privacy@4ax.com...

Hi,

this is an interesting challenge, if someone suggests a working solution, I will link it to my page.

Thanks,

Bruno

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Reply to
BrunoG

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There was a failed project with thermal cameras tracking customers walking through a shop.

It failed for various reasons (management mostly) but it used a bunch of LEDs to reset integrators.

It was pretty low-res.

Thomas

Reply to
Zak

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I believe some microprocessor based smoke detectors use a similar method to initiate a 'test' of the detector (where smoke detectors are installed in hard to reach places). A laser pointing device with a modulated signal is used. The laser is aimed at the smoke alarm LED. The modulated data is received by the LED (and thus microcontroller), and if the data is 'correct', then a smoke detector test is started. Quite a neat solution I think.

Jim

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Reply to
Jim

Nope, just a little more firmware.

John

Reply to
John Larkin

They're pitiful, especially as pv generators, and merely real bad as reverse-biased photodiodes. The active area's tiny, among other things.

John

Reply to
John Larkin

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