Getting my Gertboard working... Help!


10 posts
by karl101 » Sun Nov 04, 2012 11:10 am
Hello,
I've built my Gertboard. Checked it over three times, all the surface mount components are cleanly mounted, checking for shorts finds nothing, the resistor packs are all mounted so the dot on the pack matches the marking on the board, the IC's are in their proper places, and the right way round. The various places marked 3.3v are as expected, the Pi's power supply is 1200mA

Yet I cannot get it to work using the test leds-rp.py from here: http://raspi.tv/tag/gertboard-software .

When I place my hand near the LED's they light up, I have made a video demonstrating this: http://youtu.be/Xlm41Cr8fOQ this, to me, suggests I have done something wrong.

Any ideas?
Thanks

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by karl101 » Sun Nov 04, 2012 11:45 am
The second paragraph should read:

Yet with the board setup for the LED test as in the user manual cannot get it to work properly using the test leds-rp.py from here: http://raspi.tv/tag/gertboard-software . The LED D5 illuminates half-heartedly or not at all when the program is run, it is connected the right way round.

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by DirkS » Sun Nov 04, 2012 12:17 pm
See this thread: viewtopic.php?f=42&t=21644

Gr.
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by karl101 » Sun Nov 04, 2012 1:26 pm
thanks, but mines an rev1 board.

What about the glowing LED's when my hand is near?

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by mahjongg » Sun Nov 04, 2012 1:42 pm
I don't know anything about the gertboard, haven't even seen the schematics, but the "hand effect" strongly suggest the LED's are driven by a CMOS device (74HCxxxx perhaps) that doesn't have its input connected to anything, so is very sensitive to any electric fields that your hand happens to emit. perhaps somehow you forgot to connect the inputs of the LED drivers to the GPIO's. Isn't it so that the gertboard can be configured using jumpers? Perhaps you simply forgot to place the right jumpers.
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by alexeames » Sun Nov 04, 2012 3:00 pm
It could be a software issue, but it works fine for me, so I can only think that maybe you've got something wrong with the wiring? Have you got all 12 (or less if using less wires) jumpers on the output positions above the buffer chips?

Edit to add:
Having watched your video, I see that you don't have any jumpers placed on the output positions above the buffer chips. The wiring diagram in the Gertboard manual page 16 shows the need for jumpers in these positions so the board knows those channels are outputs. You've left them floating.

Phew - I thought it might be my software. :lol:
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by karl101 » Sun Nov 04, 2012 4:32 pm
Hello

No its not the software the program works, I've wired and set the jumpers for the LED test. The LED's still go on and off if I wave my hand around the board, its like a rubbish magic trick. I have used all the wires that come with the kit which is enough for all but the last three connections.

If I touch any of the metal parts on the Pi, like the Ethernet port, the LED's go out. So it seems to me there is some sort of grounding problem.

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by alexeames » Sun Nov 04, 2012 4:52 pm
Quite a few people have had this. I was alarmed by it when I built mine, but don't worry, it's perfectly normal. I documented it in late September in a thread called something like Gertboard is a proximity sensor.

There's also a link to one of my blog posts about it and a video in this post here...
viewtopic.php?p=197672#p197672

The reason for it is that the buffers don't have pullup resistors because Gert didn't want to torture us all by making us add another 12 surface mount components. :D At the time, I didn't even know what a pullup resistor was (and I think I only partly know now - LOL) so if you're like me, you wouldn't have understood the part where this is mentioned in the manual. :lol:
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by Grumpy Mike » Sun Nov 04, 2012 6:36 pm
karl101 wrote:If I touch any of the metal parts on the Pi, like the Ethernet port, the LED's go out. So it seems to me there is some sort of grounding problem.

This page was written for the Arduino but it is true of all electronics including the Pi with a Gert board:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html
It explains what is happening.
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by alexeames » Sun Nov 04, 2012 7:19 pm
Grumpy Mike wrote:
karl101 wrote:If I touch any of the metal parts on the Pi, like the Ethernet port, the LED's go out. So it seems to me there is some sort of grounding problem.

This page was written for the Arduino but it is true of all electronics including the Pi with a Gert board:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html
It explains what is happening.


Excellent - thanks Mike :) I think I DO know what a pullup resistor is now :D
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