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Thread: Teensy 3 and DMX

  1. #1
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    Teensy 3 and DMX

    Hello,
    I'm about to build a simple DMX to midi interface using a teensy 3.

    I was thinking about using this schematic : http://www.makesomecode.com/wp-conte...09/12/dmx1.png

    Will this also work at 3.3v using the teensy or do I need to power the thing with an external 5v adapter ?

    Thanks !

  2. #2
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    Ahhh I think I answered the question myself. I just need to use the vin pin I assume to get the 5V ?

  3. #3
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    To supply power to the Teensy3 you can use 5V on the VIN pin as the Teesny has its own 3.3V regulator on-bard. However, the IO on the Teensy3 is not 5V tolerant and you'd need an appropriate (100Ohm ?) series resistor, to "protect" the pin.

  4. #4
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    Even if the pin is an output ?

  5. #5
    Senior Member PaulStoffregen's Avatar
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    That circuit should work, if the SN75176 chip is powered by 5 volts. The chip accepts TTL levels, so you can directly connect Teensy3's pin 3 to the input pin on the SN75176.

    You might consider using a better chip, like a MAX483 or MAX487. Those chips consume much less power. They also have a slew rate limiting feature on the output pins, which dramatically improves signal quality if there's no termination resistor at the end of the cable. The slew rate limit does restrict the max recommended baud rate to 250 kbps, which is fine for DMX. They use the same pinout, so they're drop-in replacements.

  6. #6
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    Thanks for the tips Paul !
    I already have the SN75176 but I'll socket it so I can drop a MAX483 or MAX487 if I run into problems.
    Here's the board layout I did :
    Click image for larger version. 

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  7. #7
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    I noticed this is the same circuit as what's on the Arduino web site. Is there a reason the driver and receiver are enabled at the same time and the receiver output is dumped into a load resistor?

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