Forums

using a LED as a light sensor

Started by BrunoG May 6, 2006
Hi,

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

http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html

Questions & comments are welcome !

Thanks,

Bruno 


BrunoG wrote:
> Hi, > > Here is an idea about using a LED as a light sensor, to dim a 7-segments LED > display : > > http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html > > 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.
BrunoG wrote:
> Hi, > > Here is an idea about using a LED as a light sensor, to dim a 7-segments LED > display : > > http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html
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.
BrunoG wrote:

> Hi, > > Here is an idea about using a LED as a light sensor, to dim a 7-segments LED > display : > > http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html > > Questions & comments are welcome ! > > Thanks, > > Bruno > >
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
On Sun, 07 May 2006 00:42:14 -0700, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

>BrunoG wrote: > >> Hi, >> >> Here is an idea about using a LED as a light sensor, to dim a 7-segments LED >> display : >> >> http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html >> >> Questions & comments are welcome ! >> >> Thanks, >> >> Bruno >> >> >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)
--- Fluorine Hexasulfide? Must be some nasty shit... ---
>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,
--- a bug in the system? ---
>LEDS and even Silicone photo detectors
--- Aren't those the kind you spray in place? ---
>are not sensitive >enough for that application. (at least they wasn't back >when it was designed).
-- John Fields Professional Circuit Designer
On Sun, 7 May 2006 01:30:42 +0200, "BrunoG" <please_reply_in_the_forums@www.micro-examples.com> wrote:

>Hi, > >Here is an idea about using a LED as a light sensor, to dim a 7-segments LED >display : > >http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html > >Questions & comments are welcome ! > >Thanks, > >Bruno >
Mistubishi Electric Research Labs published a paper describing using a led for bidirectional communications. Do a google search for "TR2003-35".
Jamie wrote:
>
... snip ...
> > 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).
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 "show options" at the top of the article, then click on the "Reply" at the bottom of the article headers." - Keith Thompson More details at: <http://cfaj.freeshell.org/google/> Also see <http://www.safalra.com/special/googlegroupsreply/>
On Sun, 7 May 2006 01:30:42 +0200, "BrunoG"
<please_reply_in_the_forums@www.micro-examples.com> wrote:

>Hi, > >Here is an idea about using a LED as a light sensor, to dim a 7-segments LED >display : > >http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html > >Questions & comments are welcome ! > >Thanks, > >Bruno >
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
On Sun, 07 May 2006 09:19:49 -0700, John  Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

>On Sun, 7 May 2006 01:30:42 +0200, "BrunoG" ><please_reply_in_the_forums@www.micro-examples.com> wrote: > >>Hi, >> >>Here is an idea about using a LED as a light sensor, to dim a 7-segments LED >>display : >> >>http://www.micro-examples.com/public/microex-navig/doc/096-led-light-sensor.html >> >>Questions & comments are welcome ! >> >>Thanks, >> >>Bruno >> > >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 | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.

John Larkin wrote:

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