So I am wanting to make a custom LED scrolling message display. Basically I have a surface I am going to mount 32 LED's to and then have them controlled by an Arduino. What kind of hardware would I need and what would you suggest for a power source, I want to go as light and compact as possible.
5 Answers
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I guess it depends on the rating of your LEDS a bit -
But you will need to look at expanding the Arduinos digital outputs by using some latching Shift Registers.
Once you've worked out what rating LEDs your using you can get a better idea of what power source would be the best. If your just using standard LEDs (around 20mA) there's no reason you couldn't power the whole lot from a 9v PP3 battery, you could even use a smaller equivalent 9v battery to get the size and weight down - but the smaller you get the less it's life span will be.
I use an Arduino, 3 x 595 Shift Register and one of these Bi-colour Red Green LED matrix - the whole lot is powered by a PP3 9v battery and it'll last around 30 hours of solid LED scrolling fun!
Here's a video showing my matrix if you're interested.
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You could also use a Maxim MAX7219, could save some PCB space with it.
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I'm working on a similar project for an R2D2 build with Arduino.
I've gone through the following project progression so far:
- Wire eight LEDs (directly) up to Arduino with a breadboard, make them blink randomly. Not too difficult.
- Charlieplex six LEDs with three lines via Arduino, make them blink randomly. A little more difficult, but not too bad.
My next project is designing (on paper) the Charlieplexing circuit for the 8x5 LED array. This will require seven lines, though I will probably use eight to simplify the wiring.
My plan is to wire all this to the Arduino board with an eight pin ribbon cable, making everything all nice and tidy.
I hope all of this helps...if I understand you correctly, the only thing that would be different between our two projects would be software. As far as power, I'm pretty sure that Arduino should be able to drive that many LEDs without too much trouble. Ultimately I'll be relying on Li batteries, but in the meantime, I just use the 5v from the adapter.
08-13-2010 - I just found this.
It looks like both of our projects are subsets of this one. I bought one, and I expect that the wiring on the board will give me the education I need.
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\$\begingroup\$ I hope that by "on paper" you mean "in schematic form" rather than with a pencil and some shredded trees. Using any electronic schematic capture program will aid you in editing and viewing your schematic. The ability to highlight nets and move component groups around is a wonderful thing. For this project, I'd probably choose to use a simulator, so you can make sure that you've got the wiring correct. \$\endgroup\$ Commented Aug 12, 2010 at 15:26
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\$\begingroup\$ Also, traditional Charlieplexing gives you control of n^2-n LEDs with n control wires. So, I don't see how the irregularity of an 8th line will help the wiring. Why not make an 8x7 LED array? Having 8 lines will simplify the programming and the hardware. \$\endgroup\$ Commented Aug 12, 2010 at 15:30
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\$\begingroup\$ Just because it's an 8x5 array. The reason that it's 8x5 is because it's part of a prop: artoo-detoo.net/tag/front-logic Otherwise, you're absolutely right. \$\endgroup\$ Commented Aug 12, 2010 at 16:56
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\$\begingroup\$ Well, I use ExpressSCH, but in this case, I really do mean pencil and paper. I think there's a lot of value in stepping away from the technology from time to time. Once I've reached a certain point in the p&p I'll move it into the software. \$\endgroup\$ Commented Aug 12, 2010 at 16:57
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I did this project with 10mm LEDs in a 2 inch grid in a wood frame. I used an ATtiny2313 to drive the cathodes of 8 LEDs at one time, four transistors switch between the columns of anodes, and the chip runs off its internal oscillator at 8MHz. A MAX2313 drives the serial port.
A special 4-pixel wide font fits on this very low resolution display. An attached computer sends 32-byte frames (8 bits of brightness per LED) over a serial port. Scrolling text at this resolution and size was rather unsatisfying so instead I flash each letter of the message.
The code is available on Google Code.
answered Aug 16, 2010 at 14:03