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Support Forum » Unable to get led array to work with Raspberry Pi

June 04, 2013
by JackScumm
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Hi,

I have built the led array as per instructions. It works perfectly with my Windows PC. Now I would like to plug it in my Raspberry Pi.

I plug it in and it starts displaying the test pattern as expected.

Next I run python-listener.py on the Raspberry. I start it by this command:

pi@raspberrypi ~ $ python python-listener.py &

It starts to run in the background. Then I enter the line to echo something to the array:

pi@raspberrypi ~ $ sudo echo "FOOOO" | netcat localhost 6667

Only thing that happens is that the array quits displaying the test pattern. No output of the text I entered.

Note that I don't have a keyboard or display connected to the Pi, I use Putty to connect to the Pi using SSH and run the commands from there. Could this be the cause of my problems?

All help appreciated. /Jack

June 05, 2013
by Rick_S
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I'm not exactly sure what it is used for on the pi, but I think it's uart is by default not available for other uses and must be released to use it. Adafruit has a write up on that process at this link.

If you did this, then the only other thing I could think of could be the 3.3V logic on the pi not being enough if you are running the array ay 5V. Also,you could damage your pi if you have both transmit and receive lines hooked up without any voltage level converters.

Hope that gives you some ideas to look at. If you already did all that, then I'm not too sur why it isn't working.

Rick

June 05, 2013
by JackScumm
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I looked at the instructions from Adafruit and tried that, unfortunately that didn't help.

Some more info that might be useful. After the echo command, I get this output.

Connected by ('127.0.0.1', 40490)
June 06, 2013
by JackScumm
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And more more thing. The array uses an external power source, so it is not drawing power from USB.

June 06, 2013
by JackScumm
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And yet one more update. Referencing to this post: http://www.nerdkits.com/forum/thread/259/

I made a python script that scrolls a hard coded string. That works! So my problem has to be that as I connect to by Raspberry from a PC using Putty, and try to enter strings from the keyboard on that PC, the array doesn't see that input. It just waits there for input that never comes. Any idea how I could direct the input from my PC, using Putty connected to the Pi?

June 06, 2013
by Rick_S
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I wasn't referring to the array using external power, I knew that it did. I was referring to the fact that the power used by the array is 5V, thus the I/O is also 5V.. The raspberry pi has 3.3v I/O. It has no on board buffers. The 5V Vs. 3.3V communications between the two "could" pose a problem if no level converters are used, and could possibly damage the raspberry pi's serial input.

Even though you have seen results hard coding strings, you should look into level converters to make sure your pi doesn't get hurt by over voltage.

Rick

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