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THVD1410: LEDs on datalines RS485

Jesse van der Zouw
Intellectual 955 points
Part Number: THVD1410

Is it acceptable to use a 1mA led on the RS485 datalines to give visual feedback about data activity?

  • 0
    TI__Mastermind 25705 points

    Hi,

    It's an interesting idea. Would you put the led between A and B or from A/B to ground? RS485 drives about 30mA during normal operation. If the load led creates is kind of symmetric to A and B pins, this scheme may work. However more commonly I see people put led at the receiver output (R, pin 1) as indicator.

    Regards,

    Hao 

  • 0 in reply to Hao L
    Intellectual 955 points

    Thanks for your reply Hao

    Input-side would also be possible, but I would prefer the LEDs to be based on the actual output.

    I was thinking about putting putting the LED in between A and B. Then if a '1' is send on the dataline, the LED will blink.

    Would that be possible? What would an assymetric load do, is the device protected against that in some kind of way?

    edit: Or even put two leds in opposite polarity, then they will blink with any data activity.

  • 0 in reply to Jesse van der Zouw
    TI__Mastermind 25705 points

    I think the theme would work although not ideal. When '1' is sent, the voltage of A will become lower due to the extra LED load. However if the receiver input is still large enough, RS485 communication should still work.

    Regards,

    Hao