In article <4o4qnr$> (Stefano Mosca) writes:

>   I need a simple circuit to use a photodiode to detect an IR beam, such
>   as that coming out from a remote control, so that I can try and see
>   the shape of the signal on an oscilloscope.
>   Thanks in advance
>   Stefano Mosca

Try this:

--- sam

IR detector circuit:

This IR detector may be used for testing of IR remote controls, CD player
laserdiodes, and other low level near IR emitters.  Alternatives to the
use of this circuit for some applications include an IR detector card
(available at Radio Shack - sensitivity from 600 to 1500 nm, catalog
number 276-1099, $5.99) or a camcorder having a CCD type image sensor
which may have some sensitivity to IR.

Component values are not critical. Purchase photodiode sensitive to near
IR - 750-900 um or salvage from optocoupler or photosensor.  Dead computer
mice, not the furry kind, usually contain IR sensitive photodiodes. For
convenience, use a 9V battery for power.  Even a weak one will work fine.
Construct so that LED does not illuminate the photodiode!

The detected signal may be monitored across the transistor with an

 Vcc (+9 V) >-------+---------+
                    |         |
                    |         \
                    /         /  R3
                    \ R1      \  500
                    / 3.3K    /
                    \       __|__
                    |       _\_/_  LED1 Visible LED
                  __|__       |
        IR ---->  _/_\_ PD1   +--------> Scope monitor point
          Sensor    |         |
        Photodiode  |     B |/ C
                    +-------|    Q1 2N3904
                    |       |\ E
                    \         | 
                    / R2      +--------> GND
                    \ 27K     |
                    /         |
                    |         |
       GND >--------+---------+

Date: 25 May 1996 10:40:55 GMT

Original Subject: Re: Help: need simple circuit to use photodiode

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