[chbot] Anyone tried LEDs as light sensors

[Charles Manning]

Hi Stephen

Do you have a url for this? I searched the Freescale (ex. Motorola) site and 
TI (since they make the MSP430) and did not find anything.

-- Charles

On Wednesday 12 November 2008 10:26:25 Stephen Irons wrote:
> You can get the same effect from transistors -- any semiconductor
> junction. I once filed off the top of a BC109 transistor -- this is in a
> metal can so it was easy to do. I have no idea how long it will last
> before the air or dust does some damage to the junction.
>
> Motorola has an application note for their MSP430 series
> micro-controllers where they use PWM to control the brightness of an
> LED, and during the off period, it sense the brightness of ambient light
> using an A-D converter to measure the junction voltage of the LED.
>
> Stephen Irons
>
> chchrobotics-request at lists.linuxnut.co.nz wrote:
> > Date: Mon, 10 Nov 2008 13:00:58 +1300
> > From: "Charles Manning" <cdhmanning at gmail.com>
> > Subject: [chbot] Anyone tried LEDs as light sensors
> > To: "Christchurch Robotics" <chchrobotics at lists.linuxnut.co.nz>
> > Message-ID:
> > 	<2e228380811091600s339f3ad7yee7b9ee1b231a75a at mail.gmail.com>
> > Content-Type: text/plain; charset="iso-8859-1"
> >
> > I've been playing around a bit with light sensors and found some threads
> > on using LEDs as light sensors.
> >
> > Yes, not only can LEDs be used to **make** light, they can also be used
> > to **detect** light by reverse biasing the LED
> >
> > ie. by the wonders of ASCII art...
> >
> >      Ground ---|>|------- ADC pin
> >
> > Testing with an arbitrary LED from my junk box this gave a voltage of
> > very close to zero when dark and almost 1V when pointed towards a bright
> > light.
> >
> > That's quite a useful property given how easy it is to get LEDs relative
> > to phototransistors etc.
> >
> > Regards
> >
> > Charles
>
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