TX RX indication LEDs

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CrabMan

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Hello Everyone,

I am designing a RS485 circuit, the Uart to RS485 conversion is being done by MAX3485, both micro-controller(silicon Labs c8051f350) and MAX ics are on 3.3V power rail, I am thinking about adding communication indication LEDS to the circuit, what I have in mind is to connect LED's in series between MAX and controller
e.g:
Controller TX ->|- MAX DI
MAX RO ->|- Controller RX


Will it distort the logic levels?
if we consider 3.3Volt system, a nominal drop of 0.7V should not effect circuits logic levels/signals

Please comment

Regards,
 

Hali,

You have a litle bit problem in my opinion, than a LED has drop of 1.7-2.7V, depending of type...
K.

Added after 3 minutes:

What about over a second Max (with tha far side IC a3th) on the data line?
Its receiver output can drive a LED_these indicate for you a "TRX flow" on diff pair, cannot tell for you if its a receiveing or transmitting, but only>>"data data flow is active"...
RX output delivers abs. min. 5-6mA what is OK for moderner LEDs, you must only select a version/technology that works with your logical peak voltages of RX Data out?
 

Your ICs will be better off if you drive LEDs with additional NPN transistors .. see attached picture ..

Rgds,
IanP
 

    CrabMan

    Points: 2
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Clear- better!
K.
 

    CrabMan

    Points: 2
    Helpful Answer Positive Rating
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