Digital IO Extension Board - RS485

Discussion in 'The Projects Forum' started by tudstudent, Mar 30, 2015.

  1. tudstudent

    Thread Starter Member

    Jun 6, 2009
    20
    1
    With this topic I would like to request feedback for a project I am busy with for some time now.
    I am looking for feedback on the schematics as well ass the board layout/routing. I am no electronics engineer and this schematic is what I think should be working in "my theoretical world". However I would greatly appreciate if some of you experts would take a look.

    Primary functions:
    • Switching 7 12V push button led lamps (build in the push button) (X2 X3 X4 X5 X18 X19 X20);
    • Switching of 2 solenoid's (24VAC) - (X1 & X17);
    • Switching of VAC lamps/outlet (230VAC) - (X13)
    • Detection of 7 push buttons pressed (X6 X7 X8 X9 X14 X15 X16);
    • Detection of 230VAC lamp switch on/off - (X12);
    Transformer:
    • (1 transformer -> 1 primary - 2 secondary )
    • X11 = 16 VAC input from a transformer
    • X10 = 24VAC input from a transformer
    Items which I am unsure about:
    • RS485 circuit in general (1 resistor or jumpers with additional 2 resistors to ground en 5V?);
    • Ground plane?
    • 60 ohm resistor on the 24VAC to power the solenoid?
      (solenoid characteristics: 370 mA inrush, 210mA holding, 50 HZ)
    The print needs to be manufactured by a local company. Furthermore the print will be assembled in a watertight ABS enclosure.

    Thank you in advance.
    Board_rev5.png
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    I have only had a quick look but I think your VO14642AT opto-mosfet devices are incorrectly wired - check the data sheet.
    Unless your symbol is incorrect. You seem to have N-channel devices with the source going to the positive supply.
     
  3. tudstudent

    Thread Starter Member

    Jun 6, 2009
    20
    1
    Symbol is correct, I did it wrong.
    Thanks, I will correct it.
     
  4. tudstudent

    Thread Starter Member

    Jun 6, 2009
    20
    1
    Attached adjusted drawings (board and schematic)
    Board_rev6.png
     
  5. tudstudent

    Thread Starter Member

    Jun 6, 2009
    20
    1
    Small bump. Could someone please be so kind to comment on this?
     
  6. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,129
    266
    I see no protective elements on your RS-485 lines.
    This is a risky proposition for any real-world application.

    Our fist version was naked like that, suffered as a result from nasty field failures and unhappy customers.


    Have a look at the attached file, this is what we ended up with, not one failure since.
     
  7. tudstudent

    Thread Starter Member

    Jun 6, 2009
    20
    1
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