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16  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: July 03, 2010, 06:22:12 am
There's also one other thing I'm unsure of.

The RGB components of the matrix each have different forward voltage requirements and luminosities.



Green and blue have similar characteristics, red is the odd one out.

Afaik the TLC5940 looks after the current via the setting of the resistor on IREF, will I need to do anything to deal with the differing requirements between R and G/B?
17  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: July 02, 2010, 01:44:25 pm
Hi

Well, nearly a year later I've come back to this project.  I ended up finding a darlington array that can source the current my RGB matrix will require (UDN2981AT).

To try help ensure I get the circuit right, I've mocked it up.  I'm going to produce it using perf-board.  

Understanding this is probably going to be a bit of a headache.  I've tried to label everything in the mocked version - if anything's unclear, pls let me know.

One thing I'm unsure of, is whether the 4051 multiplexer is going to be okay to control the darlington array.

Also .. the darlington array is going to have to potentially source a max of (20mA*3)*8 (480mA) on a duty cycle of 12.5%, on one output.  The unit is rated for a maximum of 500mA.

I'm not great at reading datasheets -> it seems possible, but if anyone could confirm, would be grateful.

http://datasheet.octopart.com/UDN2981A-T-Allegro-datasheet-10472.pdf

Advice would be appreciated.



Cheers

Luke
18  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 21, 2009, 08:20:02 am
Ah.. I understand now - sorry, I was being a bit dense.

I didn't look at the graph in the datasheet.  120mA max if all 8 channels are on constantly.  I'll be using a 100/8 duty cycle, so I'll be able to make use of a higher current.

one thing though - why does the graph stop giving info at 34%?
I'll have a duty cycle of 12.5% - does that mean I can't assume I'll be able to source more than 350mA?
19  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 20, 2009, 10:44:41 am
Ah - shit.  I guess I could limit current for each channel to 15mA.  Maybe I'd need to sort out something else - I'll have a think.

Out of interest - where did you find out about the 120mA?  I had a look at the datasheet (http://www.datasheetcatalog.org/datasheet/allegromicrosystems/2981.pdf) and couldn't work it out.

The datasheet mentions -500 mA for Iout .. does Iout refer to the total current from all 8 drivers?
20  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 20, 2009, 07:26:24 am
Hi Grumpy_Mike,

The FET route seems possible - but as I'd need 8 (one for each common anode), I'm thinking it would be a bit too expensive.  Your project looks great - definitely into the idea of not buying the expensive sparkfun kit.  I was thinking about using small sections of glue-gun stick as a diffuser -> where did you source yr acrylic from?

I'm going to try and get hold of an allegro UDN2981A which is another 8-channel darlington array - but this time sources current.  Hopefully that'll do it.

(I just need to remember that each one of these dense mistakes is teaching me a lesson... freaking annoying none-the-less)
21  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 19, 2009, 06:15:38 pm
hey - I've just had a thought ..

I've gotten hold of some of the darlington arrays I mentioned above (ULN2803A), but I've just realised that these sink current (providing a common source).  Afaik, the TLC5940 sinks current too...

Is there anyway I can use what I've got, or do I need to find a new darlington array?
22  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 16, 2009, 02:05:35 pm
Well, I can imagine that it'll take me a while to work out the best multiplexing routines, so there'll be instances when the rows are driven for longer than 10% of the duty cycle.  20mA is probably safer smiley

Cheers
23  Forum 2005-2010 (read only) / Interfacing / Re:  8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 16, 2009, 10:17:03 am
Thanks for the reply ajb - that makes a lot of sense.  As the arduino only allows a max current draw of 40mA per I/O pin, it looks like I'll need to amplify current (or supply a secondary pwr supply) in most situations.

The mosfet route looks like it'll be far too expensive.

I'm considering http://docs-europe.electrocomponents.com/webdocs/0881/0900766b8088183b.pdf - a 8-channel darlington transistor array.  (ULN2803A)

It's rated at 500mA, and as the 480mA is a maximum, I think it should be okay?
24  Forum 2005-2010 (read only) / Interfacing / 8x8 RGB Matrix + 2x TLC5940 + 4051? on: August 15, 2009, 11:11:14 am
Hi

I'm about to start wiring up an 8x8 rgb matrix I've bought from LEDSEE.COM.  I've got a few questions before I start, to make sure I'm going about this the right way.

Datasheet for the matrix is here -> http://www.aplomb.nl/Niels_skn/RGB%20FULL%20COLOR%20MATRIX.pdf

I intend to use 2 TLC5940 ICs to sink the current from the matrix columns (24 pins in total), and then use one 4051 multiplexer to supply V to the matrix rows from the arduino's digital out pins.

Does this sound okay?
25  Forum 2005-2010 (read only) / Interfacing / Re: HowTo track artist on stage on: August 10, 2009, 08:39:26 am
how about using capacitive (proximity) sensing?
26  Forum 2005-2010 (read only) / Interfacing / Re: Capacitive sensor matrix on: August 20, 2009, 03:20:23 pm
I've got some freescale e-field sensor ICs (MC33941) which I want to try out with arduino..  the chip allows for 7 individual electrodes and comes in a 24-pin SOIC chip

I wasn't sure how I could go about building the electrodes without fabricating some PCBs, but this guide might help - so thanks for that.

Are you thinking about using a particular chip for sensing?
27  Forum 2005-2010 (read only) / Interfacing / Re: Simple, cheap gyro for Arduino on: August 21, 2009, 07:34:23 am
How about this?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=350242331908&ssPageName=ADME:B:FSEL:HK:1123
28  Forum 2005-2010 (read only) / Interfacing / Re: sensitivity of light sensors on: August 12, 2009, 09:05:22 am
I had a check on the TI website and it looks like the tsl230 (which is the IC being sold by sparkfun - mentioned above) is now obsolete .. does anyone know what it's been replaced by?
29  Forum 2005-2010 (read only) / Interfacing / Re: Telegesis USB ZigBee Stick on: August 11, 2009, 04:39:10 am
they sound pretty good then, thx smiley
30  Forum 2005-2010 (read only) / Interfacing / Telegesis USB ZigBee Stick on: August 07, 2009, 11:36:27 am
Hi

I'm looking at ways of integrating wireless with arduino.  I'm thinking that an xbee will be the most sensible way to go, but I'd like a straightforward and reliable way to interface my xbee enabled device with my laptop.

I found a zigbee usb stick made by Telegesis - does anyone here have any experience with this?

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0191670
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