Problems Connect Reach TX pin to Arduino UNO RX pin

[Knut_F]

Hello

I want to connecting my Reach RTK to an Arduino UNO to get NMEA position feed into the Arduino.

When I use SoftwareSerial the Arduino receives the messages, no problem. The Reach is powered from the USB port, and the Arduino is powered from the Reach +5V pin. The wireing when useing SoftwareSerial is like this:

But since useing SoftwareSerial limits the baud to 9600bps, I can’t get fast enough refresh rate for my application. Therfore i want to use HardwareSerial, but the Arduino only receives garbage. (Yes, I have set the baud to the same in Arduino and Reach.) The setup for powersupply is the same but the wireing between Reach and Arduino is like this:

When I use my hobby oscilloscope i get these values:

I suspect Arduino can’t detect Reach TX low on the RX pin because the pin internally has a pull up resistor. According to this forum topic there is a 1k pull up resistor.

Do anyone have any suggestions?

Could it be an idea to put in a pull down resistor between Arduino RX and GND? How big should this be?

[Knut_F]

Hello again !

I think it must be many ways to solve this problem, I solved it by using an AND-gate soldered to a piece of prototyping board like this:

The approach I suggested in my last post by using av pull down resistor did not work!