Now I know this is going to sound odd, but I'm having issues figured out how to do the following:

- Drive several hundred 10mm single-color LEDs "simultaneously"
- Power circuit using battery pack (up to 12V)
- Keep as simple and compact as possible

If I were using RGB and/or creating an animation, I could figure that out easily enough, but the simple idea of just lighting LEDs to be static is tripping me up. My thinking is that I just treat the problem as a matrix of however many columns and rows and use shift registers and rely on persistence of vision.

I'd prefer to avoid using an MCU like Arduino, but if I'm making a static thing, a 555 or similar should be fine as a clock.

Does anyone have any suggestions to accomplish this without resorting to esoteric parts?

 

hi P,
Have you considered stepping the 12Vdc upto say 48V and connecting the LED's in a number of strings.?
POV versus light Intensity could be a problem with so many LED's
What is the purpose of this display.?
E

 

It's a changeable static display?

Or just one permanent image?

 

It's basically a panel of LEDs for a wearable costume, which is why it needs to be battery powered and as lightweight as feasible.

It's fully static. All the LEDs (as viewed by the human eye) are either illuminated or off.

Theoretically if I had the voltage, I could just do one long chain of LEDs in series and just arrange the parts in whatever layout I wanted, but I'm limited by the available 12V. Moving to a hardwired series-parallel setup would be fine, except for the issues involved with LEDs in parallel. That's why I'm thinking I'd either need to multiplex the lines or find an off-the-shelf part that can run X number of lines that contain up to Y number of LEDs.

 

Just wire all the LEDs to your power source using any series/parallel configuration along with current limiting resistors.

 

I would suggest

ALITOVE 3.2ft 60 Pixels WS2812B Individual Addressable RGB LED Strip Light Programmable WS2811 IC Built-in 5050 LED Rope Lamp DC5V Black PCB Non-Waterproof IP33 $10.88
https://www.amazon.com/gp/product/B01MG49QKD/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1

You have control over each LED in the strip. You can cut them any length & add strips together. These are about 5/8" apart. You may find different spacing.
You may find them in 12 volt.
In your case, I would set them up as a 2 dimensional array of rows & columns.
At the very least, think of all the wiring it will save you.
This is about all the Arduino program it takes to make 60 pixels green.

// How many NeoPixels are attached to the Arduino?
#define NUMPIXELS 60

void loop() {
for(int i=0;i<NUMPIXELS;i++){ //This indexes all 60 pixels & makes them green

// pixels.Color takes RGB values, from 0,0,0 up to 255,255,255

pixels.setPixelColor(i, pixels.Color(0,150,0)); // Moderately bright green color.
}
pixels.show(); // This sends the updated pixel color to the hardware.
}

 

Moving to a hardwired series-parallel setup would be fine, except for the issues involved with LEDs in parallel.

There is no issue with LEDs in parallel as long as there is a separate current limiting resistor for each string.

Bob

 

So theoretically speaking, if I have 288 LEDs that I want to be illuminated at the same time with the following characteristics:

~12V supply (also have the option of using switching regulator, so 12V is a starting point)
2.65Vf nominal LEDs @ 2mA (low current ones from Kingbright, 25mA absolute max)

I can make 72 strings of 4 LEDs in series, and each string has a limiting resistor of 680-820 Ohms?

I was looking at current balancing chips such as TI's LM3466, but at 1 unit per string, it gets expensive and sounds like it's unnecessary.

I am also considering using a constant current source in the circuit, unless it's not necessary in this application, or would cause complications. The end goal is to have a robust design that can handle a fair bit of use.

DNA, to your point, I'm not able to use strip LEDs in this project, as the spacing for each LED is different, as well as the fact that the 5mm Neopixels are no longer in production, and I need to use parts that are relatively easy to replace.

 

Just re-found on eBay, DC-DC Max 4A 4.5-32V to 5-60V.
As suggested by @ ericgibbs, would hold V to about 48V, and use 15 LEDs in series.
If 2 mA OK then 3.9k resistor in string.

 

For 2 mA, a series resistor is the preferred method of current limiting. If you were to use a constant current source, you would need one for each string just like the resistors.

Bob