PC/CP300 Electronics Laboratory II

Optoisolators Lab Requirements

Objective

Optoisolators, optocouplers, photo-isolated couplers, and photon isolators are different names for source/sensor pairs which are used to provide electrical isolation between two separate circuits. These circuits are completely separate and, typically, do not share a common power supply nor ground. An LED source is typically paired with a phototransistor, a photodiode, a light activated semiconductor relay or triac. A tungsten or neon lamp source is typically paired with a photoresistor.

• to investigate the concepts behind an optoisolator using an LED-photodiode source/sensor pair
• to use a commercial optoisolator
  

Equipment

1. debugger board, bench supply, function generator, oscilloscope
2. Green LED
3. Photodiodes: Photoconductive , Photovoltaic
4. Optoisolator: 4N26 - Fairchild , Isocom

Procedure

1. A source/sensor pair can easily be made from individual components. The diagrams below show a hand-made optoisolator using a green LED source and a "photovoltaic" photodiode and a sample circuit. Although the diagram below shows the pair enclosed in heat shrink tubing, you will not use any enclosure.
              
   The control circuit should use input from the function generator; start with a slowly varying sinusoidal. Do not forget the current limiting resistor, R1, required by the LED.
   
   The circuit under control is shown as a simple voltage divider. Put the output out to an oscilloscope.
   
   Investigate the circuit operation for:
   • different separation distances between the LED and photodiode
   • different frequencies
   • different types of functions (triangle, square wave).

   How does the signal change when you eliminate the ambient light by covering the optoisolator portion of the circuit with your hand (simulating the additional of an enclosure)? Why?
   
   Demonstrate your results to the lab supervisor.

   
   
2. Test the operation of a commercial optoisolator using a technique similar to the one above.
   
   What is the source/sensor pair in the commercial component?
   
   
3. Once you are convinced that the commercial optoisolator is working correctly, design a circuit using an optoisolator that will take an input with Vcc 0-12V and output to the LEDs on a debugger board.
   
   Demonstrate your results to the lab supervisor.