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Can receive but not send serial data (on USB)

Posted: Tue Sep 22, 2015 1:24 am
by effgee
I've built about a dozen similar ethermega-based projects.
I commonly get caught out where I've got an RS232 adaptor hooked up to D0 & D1...but that is not the case on this project. There is nothing connected to D0 & D1.

I'm connecting remotely via Teamviewer (i.e. no physical access to the project), with a high quality Lindy 5m USB cable from the EM to the laptop. I can happily see all the serial output on the monitor (running 19200 baud), but when I try to send any command it is ignored. It all worked fine when I first built and programmed the EM, conceptually nothing has changed since then, apart from the project has moved a long way. I've tried unpplugging and re-plugging the USB cable, no difference.

Reading other posts here the only possible suggestion is that the 5V on the laptop usb port may be weak, and to try running through an external powered USB hub.

Any other suggestions ? Anyone else founf the same thing ?

Re: Can receive but not send serial data (on USB)

Posted: Tue Sep 22, 2015 2:08 am
by andrew
EtherMegas can be picky with USB-only power, as they draw a lot of current due to the W5100 Ethernet controller.
Try external power, also perhaps Teamviewer isn't passing keystrokes to the serial monitor.
If this is the case try different terminal software such as Coolterm:

Re: Can receive but not send serial data (on USB)

Posted: Tue Sep 22, 2015 6:38 am
by effgee
thanks John

as it turns out, I managed to get it working, in desperation I tried using Hyperterminal (laptop at the other end was XP) and to my great surprise communication worked both ways. I ended up using PuTTy (because I'm now more familiar with that than Hyper-terminal), un-installed arduino 1.6.4 and installed v1.0.5r2 (the version I used to program it originally). Oddly enough, I could download the new program using 1.0.5, but the in-built arduino serial monitor still wouldn't work, so I really don't understand what was going on, but once the new program was downloaded I could use PuTTy to configure it successfully and the result was smiles all round.

I've had similar issues with RS232, but have always blamed it on wiring faults. Now the seed of doubt is placed in my mind that the serial monitor inbuilt to the Arduino environment is maybe a little flakier than I'd assumed.

So case closed, but I'd love to hear of other people's experiences, to better understand what really went on.