Minimatrix: A small and simple self-powered LED matrix

[nickjohnson]

After finishing radiomatrix, I found myself thinking that something much simpler might have wider appeal, not to mention being a lot cheaper. Allow me to present minimatrix:



Minimatrix is incredibly simple, especially compared to radiomatrix. It has just 8 parts in its BoM: A one-color 3cm LED matrix, an ATTiny2313/4313 to power and drive it, an 8-way resistor network, a battery holder, and two decoupling capacitors. Finally, it has a footprint for a thru-hole IR LED, making it possible to add interactivity easily and with little overhead. The IR LED footprint is situated on the back, so it can be placed then bent upwards to protrude above the matrix.

Here's the schematic:



This ought to be really cheap, and simple to assemble. I think we could do some fun things with this.

[Sjaak]

I think the icsp connector is on the wrong side. It will prolly becovered by the display.

Nice project!

[nickjohnson]

I think the icsp connector is on the wrong side. It will prolly becovered by the display.

Nice project!

Good spotting - thanks!

[nickjohnson]

I updated the board to fix the ICSP issue, as well as putting the resistors on the anodes, not the cathodes (oops!). I also reassigned the IR receiver to the RX pin, meaning it can be used for low speed unidirectional serial communication, and connected it via a resistor to an interrupt pin too, so it can be used to wake the module from deep sleep.

[abetusk]

You beat me to the punch! I've had this project idea for a while now but I hadn't gotten around to actually implementing it. Good job!

Couple of questions: Are you posting this under any sort of open license? Also, are there going to be problems with the battery hitting the leads of the matrix as it slides in? Would it be better to rotate the battery holder by 90 degress?

Again, really cool, can't wait to see an assembled prototype!

[nickjohnson]

You beat me to the punch! I've had this project idea for a while now but I hadn't gotten around to actually implementing it. Good job!

Couple of questions: Are you posting this under any sort of open license? Also, are there going to be problems with the battery hitting the leads of the matrix as it slides in? Would it be better to rotate the battery holder by 90 degress?

I post all my stuff under OSHW licenses; usually CC-BY-SA. Feel free to consider it licensed as such.

That's an excellent point about the battery holder. You probably just saved me a lot of trouble. Thanks!

Edit: Bad news: The battery holder is too wide. When rotated, its pads conflict with the LED matrix leads. I'll have to take my chances as-is. :/

[matseng]

as well as putting the resistors on the anodes, not the cathodes (oops!).

Why is having the resistors at the cathodes an "oops"? (Except for isolating the iscp a little bit from the leds...)

[nickjohnson]

as well as putting the resistors on the anodes, not the cathodes (oops!).

Why is having the resistors at the cathodes an "oops"? (Except for isolating the iscp a little bit from the leds...)

Because I'm driving the LEDs a row at a time; resistors on the cathodes would mean each row has a fixed current, which would be divided between the LEDs that are on, making the brightness proportional to the number of lit LEDs in its row. Putting the resistors on the anodes fixes that.

[matseng]

Ah yes, that's true of course... But it would have been a easy firmware fix to scan by line instead of rows.

[nickjohnson]

Ah yes, that's true of course... But it would have been a easy firmware fix to scan by line instead of rows.

True. Note how I've arranged the columns, though; they're all in order on Port B, which means I can write an entire row by copying a byte to the PORTB register, much faster than toggling each bit. The ATTiny2313 only has one 8-bit port, though, so I can't do that the other way around, sadly.

[nickjohnson]

Lots of progress on the minimatrix! Summarized here, with a video: http://www.arachnidlabs.com/blog/2013/03/15/introducing-minimatrix/

[nickjohnson]

Minimatrix just went up on Tindie. It's $10, or $12.50 if you want one with an IR remote. The LED matrix manufacturer has a high minimum order, so I need a few orders to make it a go.

Also, if anyone wants to help out, I'll send a free minimatrix to anyone who contributes to the firmware. :)

[nickjohnson]

I've written up a bunch more detail on how minimatrix works and what I learned building it here: http://www.arachnidlabs.com/blog/2013/04/05/inside-minimatrix/