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Messages - michu

17
Project development, ideas, and suggestions / ExpeditInvaders, a glowing shelf you can control with your f
Hey guys

I just finished my project "ExpeditInvaders", a spiced up Ikea shelf! I added 40 LED modules to it and glued a keyboard on the bottom of the shelf. Now I can change the colorset or animation with my foot!

Links:
Blog entry: http://neophob.com/2012/08/expeditinvad ... kea-shelf/
Flicker: http://www.flickr.com/photos/pixelinvad ... 988401736/
GitHub: https://github.com/neophob/ExpeditInvaders

I hope you guys like it, if you have questions I'm glad to answer them.

Cheers
Michu
19
Project development, ideas, and suggestions / Dead simple input device
hey all

I'm working on a new Arduino project and looking for a simple, cheap and reliable input "device". I found some solutions, but not the ultimative solution. Here's my list:

Native Capacitive Sensors without additional Hardware: http://arduino.cc/playground/Code/CapacitiveSensor
Capacitive Sensing Library: http://arduino.cc/playground/Main/CapSense
Pro: very easy, Con: Not reliable if Arduino is not Grounded, ESD (fry the Arduino?)

PS2 Scroll Wheel Mouse: http://thepotterproject.net/TPPNews/?page_id=180
Pro: easy, nice control, Con: looks ugly

Push Button and Arduino internal Pullup Resistor: http://sheepdogguides.com/arduino/aht0button.htm
Pro: also easy Con: needs Push Buttons/Hardware case

Does someone else knows some more easy input devices?
24
Project logs / Re: Huge Led Pixel Matrix
Hey guys

I'm updating my PixelController software and did some major updates like an integrated GUI, Color Sets etc. Take a look at the Screenshot, the code is on GitHub.

I hope you find it useful!

Cheers
Michu
25
General discussion / Re: SPI Signal, long cable and some questions
Quote
Not necessarily. The noise at the low level (cyan trace) is severe and you even have a glitch. That looks a bit like cross-talk between the clock and data lines. Definitely a sign of problems.
Full ack, my cables are just not really suitable for this kind of signals. I just ordered some cables and soldered some connections on it... I never realized why there exists twisted pair cables and straight cables, until now (or when my issues started...)!

Quote
The problem is not the master PSU, but what you have locally. You can have a lot of noise on the buffer's supply, even with a rock stable master supply. The cables are your worst enemy. That is why I wrote about the bypassing and the ferrite bead placed locally.

You should have the probe on the local Vcc/GND pins (at the 5V part) and see what it shows there (use only one scope trace with a floating setup). The buffers are sourcing and sinking a lot of current (probably > 100mA).
Well I throw away my buffers and drive the whole thing with my teensy board. I couldn't see any advantages by using a buffer driver, I just added a 1 kOhm resistor between CLK and DATA in each module. Each module has a simple power supply on it (also 50Ohm decoupling resistors) so I guess thats ok. My problem is that I don't really have a studio with alot of components, so I have to order every simple component, thats the reason I didn't try the ferrite bead.

Quote
500kHz is a real pain, but you should be able to press 10MHz through the line if setup correctly and all is matched. I pressed 8MHz TTL CGA signals through 15..25m of cable with proper buffering and termination without a hitch.
Do you have released some information about your projects? Sounds interesting.

Meanwhile I use 125kHz, and it works fine! And I really don't want to debug my installation further, I already invested too much time into that project, I'm just glad it works!

thanks again for your help!
cheers
michu
27
General discussion / Re: SPI Signal, long cable and some questions
Wow, thanks guys for your reply. My original idea was to use a schmitt trigger to reshape the flanks/edges of the signal. however a friend of mine had similar issues (with a ws2801 led driver while i use a lpd6803 led driver) and used severall bus drivers to fix his issues. as my electronical skills are quite limited i just tried his approach.

@arhi:
Quote
what is the distance between the modules?
the cable-length of each between each module (just to clear things up, one "module" has multiple led modules inside, between 10 and 20) is about 70cm, the cable is think (1,0mm²) but unshielded and not twistet. I try to switch modules and cables, and the result cannot be solved with logic (maybe I've got the tunnelblick already).
Quote
You should look at the signal with and without 1k resistor with a scope
I did that, what I saw is that the Vpp level decreases about 1-2V. And yes the Quad is definitive not a pro tool, however as a hobby product its quite okey...

@Bertho
Quote
Wow, that is some noise you have there.
I guess this sigal looks like this due slow flanks time, right?
Quote
Are you sure that you have a stable power supply
I use a 500W ATX Power supply, I used this one for another project (128 Led Modules) without issues. But there I didn't had long interconnecting cables. However I'll check the power supply with my scope and check if the 12V are pulsate, thanks for this hint!

The SPI clock is quite important yes, currently I use 0.5MHz. If I double that the error rate increases significant, I think I'll lower that to 250kHz.

So, my next concrete steps will be a) recheck the Power supply and b) lower SPI clock rate.

I'll post more questions after that..

thanks again for you help!
cheers
28
General discussion / Re: SPI Signal, long cable and some questions
thanks Arhi for your reply

Quote
If I understand your blog correctly, you get the first strip to work but second strip don't and between first and second strip is a lengthy cable just like between your MCU and first strip.

correct and just a detail, I don't use strips but modules. anyway I got unit 2-6 working by adding a 1kOhm resistor between data and clock. however unit 7 and 8 are not really working correct (visible errors) thats why I wanted to add a line driver after 4 modules. according to the data-sheet my modules should regenerate the clk and datasignal after each pixel, I just discovered that the Vpp level get higher after each unit. so maybe you can help me answering some questions:
-why does a 1kOhm resistor between clk and gnd work, while a 1kOhm resistor between data and gnd does not work?
-what does the 1kOhm resistor do besides reducing the Vpp level?
-Are Zener diodes suitable in a 500kHz circuit or are there some special zener diodes available?

cheers
michu
29
General discussion / Re: SPI Signal, long cable and some questions
Ugh already more than a month passed and I still try to solve this issue. A friend of mine had a similar issue, he use a "74AC245,Bidirectional Transceiver with 3-STATE Inputs/Outputs". He was kind enough and sent me his eagle design:

[attachment=1]

If I put this driver in the beginning of my installation, it works fine. But if I put this driver AFTER the first cable, it will not work anymore (too much noise):
[attachment=0]
Output signal: yellow
Input Signal: Cyan (note the ripples, they get cutoff)

Maybe its due my used zener diode, a Diotec ZPY 5,6V 3W?

I can fix my signal when add a 1kOhm resistor between CLK and GND, this reduce the Vpp level from 6-7V down to 4-5V. however this does NOT work on the data line, why not?
And adding a 1kOhm resistor is unfortunately not THE solution, as the signal is very bad after 6 of 8 illuminated letters. thats why I want to regenerate the signal after 4 letters, thus improve the schema, any hints?

cheers and thanks
michu
30
CPLD programmable logic / Now what?
Hey guys

I just bought a XC2C64A CoolRunner-II CPLD development board, now what? What did you guys use this CPLD for?

I never worked with one, so I'm curious.

What I want to do is to create a kind of buffer chip for a spi/i2c signal (software schmitt trigger?), what do you think, is this possible? or completely the wrong approach?

cheers
michu

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