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terminals detection

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jeenanrex

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i am trying to build a proximity sensor using dual reflective sensor. it has an IR LED and a phototransistor in a single casing with a thermal and opaque shielding between the two. the ir rays are reflected from any object and the phototransistor detects it.

the sensor has 4 terminals. two of the LED and two from the collector and the emitter of the phototransistor while the base current is controlled by the intensity of IR rays incident on it.

The problem is identifying the terminals. any ideas about how to identify it?
 
Hi Rex,
You have an LED in there so it is easy to find with a multimeter set to measure the forward voltage drop across diodes. The LED will measure about 1.3V.
With the LED conducting a few milliamps through a current-limiting resistor you can detect the polarity of the collector and emitter by connecting a power source of 6V or less (to avoid an excessive reverse emitter-base voltage if you connect the polarity backwards) in series with a current-limiting "collector" resistor. The transistor will probably conduct a little even with reversed polarity but will conduct much more with correct polarity. Turn the LED off and on a few times to make certain that the transistor follows it.
 
I wod do it simply by puting an multimeter on diode test and try the pinc

on the LEDs terminals its shod be 1.3-1.9kOhm (depends on the multimeters mesuing voltage)one way an infinite the other.

as for the fototransistor try the pins and point it in light (to a light bulb or out the window)and wen you wave your had in front of it its resistance shod change (use diode test or Mohm range)
 
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