Wanted: Simple Light Detector Circuit

R

Radio Man

Guest
I need a sensitive light detector that i can place in front of the eyepiece
of
a binocular. This detector should sound a "beep" whenever it detects light.
I would also like it to be powered by 6 vdc or less.
 
Radio Man wrote:
I need a sensitive light detector that i can place in front of the eyepiece
of
a binocular. This detector should sound a "beep" whenever it detects light.
I would also like it to be powered by 6 vdc or less.
Click to expand...
What amount of light? A star bright star in view? Headlights 50 feet
away shining directly on the binoculars? Sunlight? That covers a
range of millions to one, I think.

--
John Popelish
 
I should have been specific....."Starlight" is what i want to detect.
"John Popelish" <jpopelish@rica.net> wrote in message
news:4165EE31.1564B157@rica.net...
Radio Man wrote:

I need a sensitive light detector that i can place in front of the
eyepiece
of
a binocular. This detector should sound a "beep" whenever it detects
light.
I would also like it to be powered by 6 vdc or less.

What amount of light? A star bright star in view? Headlights 50 feet
away shining directly on the binoculars? Sunlight? That covers a
range of millions to one, I think.

--
John Popelish
Click to expand...
 
Radio Man wrote:
I should have been specific....."Starlight" is what i want to detect.
"John Popelish" <jpopelish@rica.net> wrote in message
news:4165EE31.1564B157@rica.net...
Radio Man wrote:

I need a sensitive light detector that i can place in front of the
eyepiece
of
a binocular. This detector should sound a "beep" whenever it detects
light.
I would also like it to be powered by 6 vdc or less.
Click to expand...
The basic photo diode amplifier is shown on page 6 of this opamp
reference:
http://www.national.com/an/AN/AN-20.pdf

If you connect a second opamp as a comparator you can drive a small
piezo buzzer directly from the second opamp. Since opamps amplify the
difference between their two inputs, you connect the output of the
first amplifier to one of the second one's inputs and connect the
other input to a trim pot connected as a supply voltage divider that
can produce any voltage between the positive and negative supply
rails. I think I would start with a pair of 9 volt batteries
connected in series as the supply, (18 volts total) with the junction
between them as the signal ground. An LM358 dual opamp might be good
enough and is very common.

Here are the data sheets for some photo diodes sold through Digikey.
http://rocky.digikey.com/WebLib/Sharp/Web%20Data/bs520.pdf
http://www.photonicdetectors.com/pdf/pdbc107.pdf
http://www.photonicdetectors.com/pdf/pdbc113.pdf
http://www.photonicdetectors.com/pdf/pdbc140.pdf
http://rocky.digikey.com/WebLib/Photonic%20Detectors/Web%20Data/pdbc135.pdf

Here is an example of a piezo buzzer that an opamp can drive:
http://rocky.digikey.com/WebLib/CUI%20Inc/Web%20data/CEP-2260A.pdf

You may need an additional lens to form an image of the star on the
detector like your eye's lens does for your retina.

--
John Popelish
 
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