Arduino Mega - RX and TX Lights

Marty1962 Mar 30, 2019

  1. Marty1962

    Marty1962 TrainBoard Member

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    Hi Guys and Girls

    I have put together and Arduino Mega and the motor shield as required for DCC++.

    I have mounted all the pieces into a proper case but I thought it would be handy to mount led bezels in the front panel that mimic the Arduino and motor control shield lights. This is just to ensure everything is on and working once the case is screwed up and closed.

    On the mega board there are TX and RX orange leds they flash when the they are in use and I was wondering if you could simply use the other tx and rx ports on the board with the appropriate resistor of course to power the two front bezels.

    I just dont want to damage anything by doing this so thought it best to ask.

    Regards
    Marty1962
     
  2. William E Van Buskirk

    William E Van Buskirk TrainBoard Member

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    The LEDs are showing the two track outputs polarity in reference to board GND. So when A is positive, LED 'A' is forward biased and 'B' is reversed. When the DCC signal switches, the 'B' LED is then forward biased.
    So you could add two LEDs, with limit Rs, connected to the motor A and B terminals and GND for your front panel. Take a look at the Motor Shield schematic, google is your friend :)
    Bill
    PS sorry I thought we were talking about the motor shield, my bad. The Tx Rx LEDs are driven by the ATMEGA 16u2, that is providing the USB to serial bridge for the AT 2560. This smaller AT doesn't have any pins broken out for use so you would have to do some very careful surgery. I wouldn't advise it. You could add code to use a couple of the 2560's pins to show serial traffic but thats complicated also.
     
    Last edited: Mar 31, 2019
  3. William E Van Buskirk

    William E Van Buskirk TrainBoard Member

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    Another possibility would be to connect to Header pins 0 & 1, Serial 0. You would need either a couple logic gates or BJT switches, to buffer the line, that drive LEDs. These pins will be active when the two ATs are sending/receiving data.
    Bill
     
  4. Marty1962

    Marty1962 TrainBoard Member

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    Thanks Heaps Bill, some serious food for thought. The whole intent was to present what leds were active and operating, to the outside of the case, mainly for fault finding. After your feedback it maybe just easier to undo the two screws holding the lid on the case to check. Again thank you for your advice, regards Marty62
     
  5. William E Van Buskirk

    William E Van Buskirk TrainBoard Member

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    Well, good luck which ever way you go. I'm kind of at the same point, working out a case, so kind of want to do the same with panel LEDs. Looking on the web I did find a thread with someone doing the same, he ended up adding LEDs and current limit Rs between Vcc and Tx/Rx header pins (TTL serial idles at High). Very minimal and as long as the LEDs don't load the serial pins too much it will work.
    Bill
     
  6. Marty1962

    Marty1962 TrainBoard Member

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    Hi Bill

    Another possible option is to use light transporters which attach to the original board led and are fibre optic so they transfer the light to a bezel on the panel. I have attached a picture below.

    Regards
    Marty62
     

    Attached Files:

    Jimbo20 likes this.
  7. William E Van Buskirk

    William E Van Buskirk TrainBoard Member

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    Good call, I've seen 'light pipes' used on commercial products but those fiber optic 'add-on' are too cool. Not sure how to mount to SMD LEDs but food for thought.
    Bill
     
  8. Onizukachan

    Onizukachan TrainBoard Supporter

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    Canopy glue works fine. I use smd all the time attached to light pipes, diffusers, etc.
     

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