Debugging with UART and Serial to USB Cable

[Lasse]

Hi,
it seems to be so simple but I cant get it to work. I bought another Serial to USB converter than the Olimex one but this should be no problem I think. After I connected Tx, Rx and Gnd (I connected Rx to Tx and vice versa) I try to login to the serial terminal with the command "screen /dev/ttyUSB0 115200". Then a blank screen appears and nothing is written on it through booting time or even after it. I used the "A13 Debian 2GB card image without XFCE4 with GCC, GPIO, WIFI, WTHERNET, UVC, Python, OpenCV" Debian image from wiki.

I used the UART1 Interface to connect to. How do you guys debug your Olimex?

best regards
Lasse

[BJFreeman]

https://www.olimex.com/wiki/Serial_connection_to_A13

[Lasse]

Hi BJFreeman,
I already know that site and when I bought my Olimex I thought it would work without debugging through serial interface. But after a while I recognized that this wont work so I bought an Adapter (http://www.amazon.de/gp/product/B00BPWMR6W). I thought about buying the Olimex one but shipping to Germany is expensive. Now I just wanted to know whether I do something wrong or not. My module is named "TTL UART 6PIN CP2102 Module Serial Converter". I dont know whether it supports 3,3V Rx and Tx level, but it has an 3,3V output.

best regards
Lasse

[BJFreeman]

I got mine from http://www.ebay.com/itm/1pcs-USB-2-0-to-TTL-UART-6PIN-Module-Serial-Converter-CP2102-STC-PRGMR-/251039347548

the page states it is 3v3

[saand]

Hi Lasse,
the one you purchased doesn't seem to have a datasheet so its unclear if it will work with 3v3 levels or if it requires 5v levels.

a way to check if the device you purchased is working along with your computer and software is to setup a communication program, connect the device then connect rx and tx together on your device (no connection to the olimex board). when you type something in the communication program exactly what you type should show up on the screen when rx and tx is connected, when not connected any typing should not come up on the screen.
this will tell you if its your device or if its the olimex board / voltage level issues

also i assume your connecting to the correct header its the 4 pin header beside the VGA port. Also i assume you have not connected rx to rx and tx to tx. if that is the case they should be swapped over, rx to tx, tx to rx.

if you have a multimeter or oscilloscope you can also probe the tx pin on the header and make sure the software on the olimex board is sending something out of the port. If you have neither of these a resistor and LED can give you an indication as well

good luck