I'm making a PCB to be a lite-brite of LEDs. It should end up functioning like a name badge that a kid can place LEDs in and make patterns such as their name or whatever other patterns kids are into these days.
The grid is going to be 10x10 using 10mm LEDs. I'm planning on adding some helpful silkscreen telling the kids that if the bulb doesn't light, flip it around. The LEDs could be any color from Red to White. I'm thinking 220 ohms in series with each one would be the way to go. In this design each row is one continuous header, which I realize now is probably confusing for kids. Perhaps just a 2-pos header where the LED should go.
I'm also including a "blinking mode" switch using a 555 timer. I'm looking for any tips/tricks/ideas that will make my layout and life easier. I may end up putting a few of these together so saving assembly time/cost is great too. Attached is an initial schematic and layout.
Last Edit: Feb 9, 2015 0:28:28 GMT -5 by msizemore
The resistor is going to depend on the voltage supplied to each LED, and the rated LED current. 220 sounds low for a 5 volt supply. Usually 330 ohm is used but I think I would go about 600+ ohm s I can use 1/8 watt or lower resistor and the LEDs will still be very bright.
Here is a handy calculator , note that the number of LEDs will be 1 as you want to connect them in parallel and not series.
Also, will the LED's be soldered into place or are you looking to make this pluggable so LED's can be removed? LED pins are faily deleicate and a few bends will break the pins off of the LED. My suggestion would be to use RGB LEDs soldered onto your grid. Then they can use a small App to select which LEDs they want on and what color, download it to the badge. They could make it blink, scroll, change colors ect.
Some things are meant to be closed. Your mind isn't one of them.
The LEDs I'm using have a forward voltage of 1.8-4V, plus the Vce of the BJT at the bottom will take another 0.6V slice out of my available voltage, plus I have a PTC which will have a small but non-zero drop. So I should be looking at LED currents from 2 - 10mA.
These LEDs will be pluggable, I imagine they'll only see 5-10 insertions each. The app is a bit beyond me right now. That would be a fantastic intro to programming though, being able to instantly see your program manipulate a display of LEDs.