[python-uk] Pyserial on Raspberry Pi returning just "\x00" ie NULL characters

Michael sparks.m at gmail.com
Mon Jul 2 16:25:00 CEST 2012

On 2 July 2012 14:15, Stephen Emslie <stephenemslie at gmail.com> wrote:
> I've found strace to be a really valuable tool in debugging arduino serial
> communication. Not sure what your problem is, but perhaps inspecting the
> serial connection like this could help:
>     strace -e trace=read,open,write -p <process_id>
> That should print out all read, write, and open calls from your process to
> the operating system, which includes reads and writes on the connection to
> arduino.

Excellent point - I'd forgotten about strace for some reason. Would
make an awful lot
of sense here.

On 2 July 2012 14:06, John Pinner <funthyme at gmail.com> wrote:
> There are known problems with the Pi USB :
> * Some possible driver issues (to do with mixed high- and low-speed
> devices on the same hub.

This one I wasn't aware of. I might shift things about to see if that
changes things.

> * Power capacity.

Yep, I'm aware of the power issues - which to be fair I think are
perfectly reasonable.

> For example, I have a rather nice IBM USB keyboard, if I use that at
> the same time as a USB wifi dongle, the wifi stops working. A cheapo
> Kensington keyboard works fine.
> Try:
> * Checking for a healthy 4.75 - 5.25 volts between TP1 and TP2 on the Pi.
> * Installing an updated Pi kernel. Dom has just done a beta Wheezy
> image, which he thinks may have fixed the USB driver problem, but he
> wants feedback:
> http://files.velocix.com/c1410/images/debian/7/2012-06-18-wheezy-beta.zip
> * Using a decent quality *powered* USB hub (>=2.0 amps)

The actual setup I have is:

Dedicated power supply -> Pi
.. connected to a 4 port powered hub (with decent power supply).
.. with the arduino plugged into that, with it's own 9V 1.5A power supply.

So I'm pretty sure power isn't the issue (but can't rule it out).

I wasn't aware of the more recent debian image. I'll try that before hunting
around in strace output - much appreciated!


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