Hi,
Here is an idea about using a LED as a light sensor, to dim a 7-segments LED display :
Questions & comments are welcome !
Thanks,
Bruno
Hi,
Here is an idea about using a LED as a light sensor, to dim a 7-segments LED display :
Questions & comments are welcome !
Thanks,
Bruno
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.
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.
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).
-- Real Programmers Do things like this. http://webpages.charter.net/jamie_5
-- Fluorine Hexasulfide? Must be some nasty shit...
Mistubishi Electric Research Labs published a paper describing using a led for bidirectional communications.
Do a google search for "TR2003-35".
... 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.
-- "If you want to post a followup via groups.google.com, don't use the broken "Reply" link at the bottom of the article. Click on
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
Are LED's more efficient as light sensors than so called photo diodes?
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et |
Is that for continuous adjustment or just Lo/Hi operation thresholding?
"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
I suspect it is SF6:
Jon
"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
-- Yeah, I know. I was just being a smartass...
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..
"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
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
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
Nope, just a little more firmware.
John
They're pitiful, especially as pv generators, and merely real bad as reverse-biased photodiodes. The active area's tiny, among other things.
John
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