What is the use of optocoupler in this circuit?

Replies

• 

  Kaustubh Katdare

  Thread moved to electrical & electronics engineering section.
• 

  reachrkata

  I can think of only 1 reason - GROUND ISOLATION.
  
  -Karthik
  
• 

  prasadaraju

  ground isolation?
  i cant get u clearly?
  can u xplain clearly plzzzzzzzzz
• 

  Kaustubh Katdare

  prasadaraju

  ground isolation?
  i cant get u clearly?
  can u xplain clearly plzzzzzzzzz

  SMS text is strictly NOT allowed on CrazyEngineers.
• 

  skipper

  If it's a security lock, maybe the optical coupler is the switch that's opened when you go through?
  So the alarm goes if the code entered is wrong, then the switch is opened (the beam is broken)...?
  
  Given the simple design, off the top I would guess that the ICs are latches (set by the switches), the S12 is probably to reset the latch condition.
  If you don't press the buttons in the right order it doesn't latch and the optocoupler stays on so the beam is interrupted and the alarm goes?
  Or, the latch enabkes the opto, and you have to break the beam to reset the lock...?
  
  You really need more details, but I would say it's one or the other.
• 

  prasadaraju

  vcan u tell me some more about it
• 

  Muffy

  The only function of the opto-coupler in this circuit is to provide an opportunity to have a wide variety of output stages. For example you could connect a micro controller circuit at the output of the op coupler , or a simple relay , or a solenoid (door lock, since its obviously a security system).
  The presence of the opto-coupler dose not alter the operation of the circuit in anyway. But the circuit by itself has no meaning you will have to add a circuit at the output of the op coupler if you want to achieve something useful.
  
  Hope this helps :smile:
  
  Good Luck.
• 

  mishra

  can u please tell me..that why we use only NPN transistor in an optocoupler....??
• 

  reachrkata

  That is because the behavior of the component is such. Whenever a current flows through the LED in the Opto, we expect the switch (phototransistor) to close. This action is same as that of a npn transistor.
  
  - Karthik
  
• 

  prasadaraju

  can u explain the detailed operation
  can u tell me wat is the value of R8,R9 RESISTORS
• 

  shaswat

  optocoulpler is given to electrically isolate one part of the circuit to the other part. so that in case of any damage in one part will not affect the other part of the circuit.
• 

  Muffy

  @prasadaraju: Can you tell us the IC number? It would be easier to figure out the operation. It seems like a quad bilateral switch, perhaps a 4066?
• 

  prasadaraju

  ya it is 4066
  optocoupler ic is 4n25
• 

  mishra

  Hey thanks karthik...it is commendable dat u replied my ques
  i'll surely come with more queris further
• 

  unkunny

  Possibly to isolate Analog Gnd from Digital Gnd ....
• 

  prasadaraju

  
  
  
  R1-7-9=1Kohm
  R2-3-4-5=100Kohm
  R6 =10Kohm
  R9 =47Kohm
  IC1 = 4066
  IC2 =4N25
  Q1-2=BC550
  S1...11=Push button sw or keyboard
  S12=Push button normal closed
  All resistors is 1/4W 5%
  
  can i get an output of putting an led at 5th pin of optocoupler and by pressing 1,4,7 .
  will the led glows when 1,4,7 is pressed ,
  can u tell me any modifications if the circuit is wrong if u think
  please reply for all as i m in very hard situation
• 

  Muffy

  You could use an LED at the output of the optocoupler, but the more sensible option would be to neglect the optocoupler and use an LED in its place. Pressing 1,4, 7 in sequence would illuminate the LED.
• 

  prasadaraju

  the circuit is working by just pressing 7
  but can u suggest any modifications if any to get ouput by only perssing 1,4,7
• 

  Ashraf HZ

  shaswat

  optocoulpler is given to electrically isolate one part of the circuit to the other part. so that in case of any damage in one part will not affect the other part of the circuit.

  Yes, this is probably true in this case. A secondary circuit, such as for the operation of an solenoid lock would require much higher voltages and current.. which would probably fry the ICs used in the primary circuit 😀
• 

  prasadaraju

  as i m going to connect this i am getting some malfunctions in circuit ?can u help me
  
  by pressing only 7 also i am geetting output at 1st pin of optocoupler
  can you tell me why is it happening so?
  can u sugggest any other modifications if any?
  also can u clearly explain how each component working?
  please help me sir.
  
  
  
  
  
  
  
  
  R1-7-9=1Kohm
  R2-3-4-5=100Kohm
  R6 =10Kohm
  R9 =47Kohm
  IC1 = 4066
  IC2 =4N25
  Q1-2=BC550
  S1...11=Push button sw or keyboard
  S12=Push button normal closed
  All resistors is 1/4W 5%
  
  can i get an output of putting an led at 5th pin of optocoupler and by pressing 1,4,7 .
  will the led glows when 1,4,7 is pressed ,
  can u tell me any modifications if the circuit is wrong if u think
  please reply for all as i m in very hard situation
• 

  reachrkata

  Yes you will see an output at pin 1 of the Opto. But this will not be useful because the R1 = 100kOhm and this high resistance will prevent the Photo-diode inside the opto from working because the current is very low.
  
  Only after pressing 1,4,7 will the photo-diode work properly because now the current would be supplied through R7 which is only 1kOhm.
  
  To check the output here is what you can do -
  1) Connect Pin 5 of the Opto to (say) 10V through a 1K resistor and also a normal LED.
  2) Connect pin 4 of the opto to Ground.
  
  You should see that when you press 1,4 & 7, the LED would glow.
  
  - Karthik
  😁
• 

  prasadaraju

  that means
  
  that means i have to connect a 1kohm resistor and led between 5th pin of opto and 9v .....is this what you are saying
  can u reply me
• 

  reachrkata

  Exactly ! Plus also connect pin 4 to GND.
  
  -Karthik