Saturday, January 12, 2013

Electronic Circuit of Optical Shaft Encoder using Optocoupler H21A3 with Transistor

Robometricschool. - In this time i want to continue discuss about implementation of Optocoupler H21A3 component as position sensor using transistor. In here i want to give you simple electronic circuit optical shaft encoder using optocoupler H21A3 with transistor. With this circuit you can use it to detect rotary speed, position sensor, position controller, etc.

Shaft encoder or also called with rotary encoder used to change linear movement or rotary to be digital signal 0 and 1. In here rotary sensor monitoring rotary movement from other tools. You can see figure 1 to know principle of optical shaft encoder.

Figure 1. Principle of Optical Shaft Encoder

From figure 1, we can conclude that disk with hole rotate between optocoupler, in here optocoupler as rotary sensor will monitoring movement of disk with infra red light that transmitted from IR LED to the infra red receiver from photo-transistor. Digital signal will be get from infra red signal that allowed and not allowed in the disk hold. 

So with principle of shaft encoder or rotary encoder we can use on of the component optocoupler like optocoupler H21A3 that used optical photo-transistor principle.

Electronic Schematic

Figure 1. Electronic Circuit of Optical Shaft Encoder with Transistor


Component List
  1. R1  ---------------------------> 150 ohm
  2. R2  ---------------------------> 10K ohm
  3. R3  ---------------------------> 4K7 ohm
  4. Q1  ---------------------------> C828
  5. Q2  ---------------------------> Optocoupler H21A3

Circuit Performance:
  • R1 used to give forward bias to LED IR of optocoupler H21A3. R1 connected  to PIN 1 of H21A3.
  • R2 is resistor for voltage divider with pin collector (PIN 3) from H21A3 that will give forward biases to transistor Q1.
  • Transistor Q1 functioned as voltage switch that can open voltage in Out or can't open voltage in Out. It will happen according voltage bias in Base pin of Q1.
  • If infra red light from LED IR can receive by photo-transistor (infra red light not closed by disk) it will make transistor Q1 get forward bias and make Out from collector Q1 result low voltage or 0 logical. In this condition transistor work like close switch.
  • If infra red light from LED IR can't receive by photo-transistor (infra red light closed by by disk) it will make transistor Q1 get reverse bias and make Out from collector Q1 result high voltage or 1 logical. In this condition transistor work like open switch.


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