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Need help to find output of board

Discussion in 'General Electronics Discussion' started by Djsarkar, Nov 4, 2020.

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  1. Djsarkar

    Djsarkar

    46
    4
    Jul 27, 2020
    Hi
    I got board from store room don't have user manual/documents I am trying to understand connection of board

    I have attached three picture
    1. First picture, when I give the 5v input to board one red led is turning on the board
    2. Second picture show front side of board
    3. Third picture show the layout of circuit
    PC817 four pin IC
    BD140 is transistor

    How to make connection for output to check that board is working or not working?

    5V signal.jpg
     

    Attached Files:

  2. Kabelsalat

    Kabelsalat

    160
    29
    Jul 5, 2011
    That board is probably just a "opto isolated relay card" - but with a transistor output instead of relays.
    What box did you pick it out of?

    This card should not be hard to draw up schematic for one of the channels.
     
  3. bertus

    bertus Moderator

    1,892
    711
    Nov 8, 2019
    Hello,

    The PC817 chips are optocouplers.
    The BD140 is a PNP medium power transistor.

    Bertus
     

    Attached Files:

    Djsarkar likes this.
  4. Tha fios agaibh

    Tha fios agaibh

    2,166
    726
    Aug 11, 2014
    Looks like water has caused some bad corrosion.

    I can't say for sure unless you draw the circuit with resistor values, but it looks like the diode cathodes go to left side of op terminals and the transistor emitter (positive output) goes past the suitcase jumper (may be used to select either 3.3 or 5v?) and continues on to the other op terminal (+)on the right.

    It appears to be a sourcing output where you would hook up (+) op terminal to your load, (perhaps a light bulb) and the neg side of your load would go to a negative power supply (likely 5v)and the positive of that power supply would go to the common terminal on the left.

    The input should make the optocoupler feed the transistor base to switch it on.

    It may even work with a continuity tester with at least 3 volts supply across the op terminals provided polarity is correct.

    Try experimenting with a small lamp, battery and suitcase positions.
     
    Djsarkar likes this.
  5. HellasTechn

    HellasTechn

    1,556
    215
    Apr 14, 2013
    The card with the LED is most probably a micro controller board. It kind of looks like a remote controlled garage door control assembly.

    The card with the opto's and transistors is a driver card for bigger loads .
     
    Djsarkar likes this.
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    11,522
    2,654
    Nov 17, 2011
    Your images are not detailed enough for an analysis. As @Kabelsalat mentioned, draw a circut diagram from one of the channels. Should be relatively easy.

    From what I can see:
    1. It looks like the screw terminals are the inputs. Pins 1 and 2 of the optocoupler are typically the LED pins, the resistor in series limits current. The separate SMD LED and resistor are there to indicate an active input:
      upload_2020-11-6_8-33-31.png
    2. The plug terminals then would be the outputs.
    3. The optocouplers will drive the DB140 transistors for more powre.
      upload_2020-11-6_8-38-26.png

    Draw the schematic and you will see that it is a relatively simple circuit.
     

    Attached Files:

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  7. Djsarkar

    Djsarkar

    46
    4
    Jul 27, 2020
    Hi
    thanks for the many of help

    I have separate PC817 IC and BD139 is transistor so I would like to make my own

    Does this circuit make any sense to turn on the led with BD139. if its look fine than I will connect all on the breadboard to see result

    upload_2020-11-6_4-5-51.png
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    11,522
    2,654
    Nov 17, 2011
    50 %.
    Where`s the optocoupler in this circuit? As shown, the 1 kΩ resistor ties the base to GND and the transistor will be permanently off.
    That is not the trace of the output board we requested.
     
    Djsarkar likes this.
  9. bertus

    bertus Moderator

    1,892
    711
    Nov 8, 2019
    Hello,

    In your openings post you stated the transistors are BD140.
    Now you say they are BD139.
    Wich is correct?

    Bertus
     

    Attached Files:

    Djsarkar likes this.
  10. Djsarkar

    Djsarkar

    46
    4
    Jul 27, 2020
    That was only half portion, Here is complete circuit diagram

    upload_2020-11-6_4-48-49.png

    Hi Bertus
    BD140 is on the board and I have BD139 on hand that I want to use to make circuit on breadboard
     
  11. bertus

    bertus Moderator

    1,892
    711
    Nov 8, 2019
    Hello,

    So the board circuits must be different, as a PNP has other control as the NPN transistors.

    Bertus
     
  12. Djsarkar

    Djsarkar

    46
    4
    Jul 27, 2020
    Correct, BD139 is NPN transistors and BD140 is PNP transistor

    I believe my circuit is correct so should I make the connection on breadboard?
     
  13. ratstar

    ratstar

    486
    20
    Aug 20, 2018
    If you dont mind me asking, what is the purpose of the backward diode?
     
  14. bertus

    bertus Moderator

    1,892
    711
    Nov 8, 2019
    Hello,

    @ratstar , the backwards diode is there to prevent the back EMF when an inductive load , like a relays or motor , is connected.

    Bertus
     
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  15. Djsarkar

    Djsarkar

    46
    4
    Jul 27, 2020
    To prevent damage we must connect a protection diode across the load. The use of a diode in a circuit prevents sudden voltage spikes from arising when the power supply is disconnected
     
    ratstar likes this.
  16. Harald Kapp

    Harald Kapp Moderator Moderator

    11,522
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    Nov 17, 2011
    The circuit in post #10 looks correct. However, the label on the pcb in the first post says BD140. What is actually printed on the transistors?
     
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