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I am trying to interface a WRT54G serial port directly with an arduino pro micro's hardware UART by connecting RX to TX and TX to RX between the devices.

serial

converter

I have a simple code running on the arduino which outputs a character on the hardware UART in every second. If I check it with the scope or multimeter before the converter I see the jumps up to about 4.7V which is ok. On the other side of the converter all I see is some low voltage noise coming out of the pin (LV 3.3) side.

My questions:

1, Do these TTL converters needed to be feed from both the 3.3V and 5V side to work correctly?

2, Couldn't this setup be done by using 1 or 2 resistors on both RX/TX wires? I assume the resistor would only be needed on the TX line of the arduino not to overload the WRTG when it sends data. However the 3.3V might not high enough to trigger an input on the arduino's hardware uart when data coming in

What's weird in this setup that I have a working older WRTG router which is directly connected to an arduino nano (running from 5V) and no problem with the communication between them.

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  • \$\begingroup\$ Does the WRT54G serial port use 3.3V? \$\endgroup\$ – Dampmaskin Apr 14 '17 at 14:07
  • \$\begingroup\$ This type of converter does indeed need to have a power supply rail at each output voltage, and of course common ground to both. A resistive voltage divider may be an option at lower speeds. To find out if the router can accept overvoltage (if it is "5v tolerant"), you would need the specifications for the Broadcom or whatever SoC used on it - out of spec operation won't necessarily kill something immediately, but it is a bad idea and may fail at any point in the future. \$\endgroup\$ – Chris Stratton Jun 9 '17 at 15:52

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