Know any good parts for this LED display project?

[Rigby]

Hello,

I need to create a 16 character digital nameplate for a project at work.  I think I have a plan of attack firmly in mind, but I want to get knowledge from the EEVblog community in case any of you would like to share your experiences or part preferences.

The basic requirements:

• 20 single color alphanumeric characters.
• Scalable solution preferred; 5 daisy chained 4-character modules, for example.
• Must be able to change the message remotely.  (Bluetooth LE, WiFi, whatever, not necessarily wireless.  Preference for simplicity in terms of hardware required.)
• Message does not need to remain after a power failure.
• Message does not need to scroll; no fancy effects required.  Just display some text.

Drivers:

At first I looked at the MAX6953 (since I have a few on-hand) but I ordered LED 5x7 matricies which are not compatible with that Maxim chip.

The Maxim 7219 and 7221 seem pretty expensive, I think I could probably do better with a small micro behind each character, creating single 5x7 matrix modules.  I would drive single LEDs at a time in this scenario, not entire rows or columns; I think this will help keep brightness uniform, if I can switch between LEDs quickly enough.

LEDs:

I found some matrices on Jameco for $0.99 each in a closeout, and ordered a ton of them.  These are the matrices that are not easily driven from the MAX6953s I have on hand.

I could also just buy a pile of 0402 surface-mount LEDs and design the circuit board appropriately.

----

If anyone has any experience with this stuff (mikeselectricstuff...), and you don't mind doing so, please chime in with a bit of advice...  This is just a one-off prototype that I'll design and assemble myself.  Don't put a lot of thought into mass production.

If the best option would be to just buy one, that's fine.  I'd prefer to do some PCB design and solder work, but if there is a finished product that is Just Great, then please let me know.

Budget is USD$200 or less for parts.

[SL4P]

Have a look at sure electronics eBay & online (their 0832 displays may work for you), or others if you are looking for RGB.
For logos etc - you may be better looking at tiled LCD or OLED panels to get decent resolution of the graphics at a modest viewing distance.

[mariush]

You can scale it up to 4 digits easily.

A pic or arduino microcontroller, reserve 2 pins for serial input, 2 pins for serial output (to do pass through of data to the next 4-digit sets) and then depending on the type of the character matrix (common anode or common cathode)... you can use shift registers to get the 4x7 outputs if the microcontroller doesn't have enough output pins and a ULN2003A for example to sink a whole row of 28 leds to ground and turn them on.  You may also need some transistors or mosfets between the shift registers and each led if you want high currents, shift registers are usually limited to about 100mA output so if you want 20mA per led, you can't really do it. Oh yes, and the individual current limiting resistors for each of those 28 leds.

ex shift register:
http://www.digikey.com/product-detail/en/SN74HC595N/296-1600-5-ND/277246
http://www.digikey.com/product-detail/en/CD4094BE/296-2069-5-ND/67331

uln2003a (7 npn darlington array, 500mA in total, but you can use 2 and make pairs of 2 transistors for more current through each row of leds) :

http://www.digikey.com/product-detail/en/ULN2003AN/296-1979-5-ND/277624

uln2803a (just like uln2003a but it has 8 npn transistors and its a bit more expensive)

http://www.digikey.com/product-detail/en/ULN2803APG,CN/ULN2803APGCN-ND/856431
http://www.digikey.com/product-detail/en/ULN2803APG,CN/ULN2803APGCN-ND/856431

If you use soic or other surface mount components they're much cheaper, especially in volume.

[LukeW]

Austria Microsystems AMS1107

http://www.ams.com/eng/Products/Lighting-Management/LED-Driver-ICs/AS1107

Basically like a cheaper ripoff of the MAX7219.

[dannyf]

The Maxim 7219 and 7221 seem pretty expensive,

It is not that difficult to code a mcu to emulate those chips: a display routine called periodically from a timer isr, a serial slave / master and you are done.

[mamalala]

If you only need alphanumeric, you may also check out alphanumeric LED displays. Search for "14 segment", "16 segment", "starburst" or "alphanumeric LED". Those come in various sizes for cheap from China, and are usually much easier to control.

Greetings,

Chris

[Stonent]

LEDs:

I found some matrices on Jameco for $0.99 each in a closeout, and ordered a ton of them.  These are the matrices that are not easily driven from the MAX6953s I have on hand.

Those easily piggyback on ATTiny 2314/4313 chips to be driven directly.  They just need 12 pins each.

One thing to be aware of, there are 2 datasheets for those matrices floating around.

Website:

"Array polarity: 5 x 7 Cathode Column, Anode Row"

Datasheet on their site:

"Description: Column Anode, Row Cathode"

The datasheet does match the part though.  There's a datasheet on Octopart for the same part number with a Jameco logo that doesn't match the ones I have.



Right now I'm looking into I2C IO Expanders to drive them.

[Rigby]

I was thinking about that.  I think it might be fairly easy to create a single character module, and just chain them up.

[Stonent]

More info on the part that I posted.

http://hackaday.com/2012/10/12/led-matrix-pendants/

I did see a youtube video several months ago where someone took colors 8x8 matrices and made them somehow connect when stuck together and expand the total display area.

You will have to change the pin mapping for the Jameco ones, I also bought the LTP-575 LED modules that they used from Jameco for the one I made.

[macboy]

You have a reasonable budget, and since it is a one-off, don't spend too much time cost optimizing this. Consider the value of the time you will spend finding the right parts, designing a PCB, soldering, etc.  I'd recommend seriously looking at pre-built display modules like these:
http://www.sureelectronics.net/goods.php?id=2592
or
http://www.sureelectronics.net/goods.php?id=1119

These can be driven by any microcontroller using SPI/I2C serial connection.

[Rigby]

I'm looking at those, too, don't worry.

Right now, it's looking like BeagleBone Black + [insert display solution] is going to tick all the boxes.

SureElectronics is in China, isn't it?  I highly doubt I'll get any shipment from China before the end of May.  Probably going to have to fart up a veroboard solution for the demo.

[Rigby]

For the proof of concept deadline I had to use on-hand parts.

For the actual demos later in the year, I'll be using single character modules based on a very small micro that I haven't chosen yet.  I am doing this because we don't yet know just how many characters we want to display at a time, or the layout of those characters.

The 5x7 modules I'm going to use have a 0.1" (2.54mm) dot pitch and I want to fit the micro and all necessary support components between the two rows of pins on the back, which are 0.3" apart.