Splitting Serial: TX over USB, RX over TTL?

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I'm interfacing my Arduino with a Spektrum 2.4GHz satellite receiver, which sends data over 115kbps serial. NewSoftSerial doesn't work reliably at that speed, I need UART. But I also would like to keep the convenient debug output over USB.

So what I'd like to do is use the TX pin over USB and the RX pin over TTL. Has anyone done this? Is it possible without major hardware mods?

Thanks in advance
Björn :slight_smile:

2

Yes, did that although a bit different (speed 19200). I connected an Serial LCD to the TX line of the Arduino and was still able to send commands to it over the serial monitor.
The other way around should work too without hardware mod, although one question remains:

Does the spektrum needs a serial in e.g. START/STOP commands?
or does it just spits out data continuously?

3

No, it just spits out data. I tried the naive way (just hook the Spektrum up to RX) yesterday and got no data back...

4

I have personally had bad luck talking to the UART via TTL and the USB->Serial at the same time. My instinct is that you would have to cut the trace between the USB interface and RxD to enable what you are doing, and that would make it hard to program the Arduino.

Maybe the FTDI has a way to program the RxD into Hi-Z. Also, maybe the FTDI output is open-collector with a pull-up, so if you send a continuous break over USB the Arduino would see a clean signal from your TTL. These are just random thoughts though.

What I wound up doing was getting a Mega in order to get extra hardware UARTs and did my debugging there.