and put one together, which works fine.

It had an extra resistor and LED in the kit, though.

Gotta hack the code, too. "Artistic differences." Maybe.

>Gotta hack the code, too. "Artistic differences." Maybe.

You're certainly welcome to do so-- just add a header for in-circuit reprogramming.

All the 10mm LEDs work fine in mine, but it bothers me that the relative brightness between the four currently lit LEDs isn't drastic enough. What seems to contribute to this is these LEDs tend to be partially lit by their neighbor. Visually it looks like a blob of 4 LEDs of fairly equal brightness moving back and forth, but the code shows that the four active LEDs have relative brightnesses.

Can anything be done for this in software or are we at the limits of brightness differences? I understand that there's many levels of brightness, but they seem to be fairly close together on an apparent brightness scale.

Okay, so you'd like to turn up the contrast. Fair enough. We tried a lot of things, and this is the one that we liked best... but tastes do vary.

There are tradeoffs in the design process. One of the things that we did in the software was to aim for fairly smooth PWM dimming while having low power consumption. The AVR internal clock was turned down to 512 kHz, which makes for a big reduction in power consumption, but the lower clock frequency makes it harder to generate smooth PWM without visible blinking. If you don't mind higher power consumption, it is straightforward to increase the clock speed to as high as 8 MHz-- meaning that you can cycle through PWM 16 times as fast, and have 16 times the dynamic range.

Also, for the diffused LEDs, perhaps-- since you're in a dim enough environment that you can see the LEDs lighting each other --you might want to change it to only one on at a time. That won't help for the clear LEDs, though.

So... yes you can change it. Would you be interested if we were to post a couple of alternate programs? (I also have a processing sketch with the same code, making it reasonably easy to try this out, even without an AVR programmer.)

Would you be interested if we were to post a couple of alternate programs? (I also have a processing sketch with the same code, making it reasonably easy to try this out, even without an AVR programmer.)

Yes, I would like to see alternate programs.

I've posted two alternate versions that each give a narrower eye here. I'm very curious to know if you find these more to your taste.

Thanks! Might be awhile before I can try it, I don't have anything to program it yet. I've ordered an adafruit programmer kit, and some headers, but it's still on the way.

I do agree that the 4 lit LED's almost look the same, it needs more contrast. On both bright and dim mode.

I finally got the programmer built, and installed the toolchain. I much prefer the alt programs. I can barely tell the difference, but alt2 might be slightly better.

By the way, I've used the same pair of 2000mAh batteries and left it running for 2 weeks on "low". They were still going strong but seemed dim compared to plugged into the USB, so I just popped them in the charger. Fresh batteries seem just as dim though so they're probably still fine. I'll let you know how much they take.

The batteries (2000mAh Eneloops) took 950 and 970 mAh to recharge. So in 2 weeks it used less than an amp-hour. That's pretty efficient!

I know it's too late for Halloween, but if you think you're having trouble with the light bleeding into neighboring LEDs, try adding some dividers between them. Bits of card stock, black construction paper (or any color appropriate to your project), anything to keep them lighting up separately. Even just temporarily, to see if the effect really is "bleeding", or just an issue with contrast.

Black heat-shrink tubing snipped to fit over the LEDs might be nice, but might add too much thickness (judging by the pictures) between the 10mm ones... Aluminum foil might be good at blocking light, but you'd have to be careful where you stick conductive metal near circuits.

I haven't bought one of these (yet), so this is all theory on my part. YMMV, and all that.