A Surprisingly Practical Numitron Watch

Regular Hackaday readers are surely familiar with Nixie tubes: the fantastically retro cold cathode display devices that hackers have worked into all manner of devices (especially timepieces) to give them an infusion of glowing faux nostalgia. But unfortunately, Nixie displays are fairly fragile and can be tricky to drive due to their high voltage requirements. For those who might want to work with something more forgiving, a possible alternative is the Numitron that uses incandescent filaments for each segment.

There hasn’t been a lot of prior-art that utilizes Numitrons, but that might be changing, given how fantastic this wristwatch created by [Dycus] looks. With a multi-day battery life, daylight readability, and relatively straightforward construction, the Filawatch is likely to end up being something of a reference design for future Numitron watches.

[Dycus] has gone through three revisions of the Filawatch so far, with probably at least one more on the way. The current version is powered by a ATmega328 microcontroller with dual 16-bit LED drivers to control the filaments in the KW-104S Numitron display modules. He’s also included an accelerometer to determine when the wearer is looking at the display, and even a light sensor to control the brightness of the display depending on the ambient light level.

If there’s a downside to Numitron displays, it’s their monstrous energy consumption. Just like in the incandescent light bulbs most of us have been ditching for LED, it takes a lot of juice to get that filament glowing. [Dycus] reports the display draws as much as 350 mA while on, but by lighting it up for only five seconds at a time it can be checked around 150 times before the watch needs to be recharged.

Its been a few years since we’ve seen a Numitron watch, and it’s interesting to see how the state of the art has advanced.

[via /r/electronics]

New Part Day: I2C In, Charlieplexed LEDs Out

It seems that most of the electrical engineering covered on Hackaday concerns exactly one problem domain: how to blink a bunch of LEDs furiously. There are plenty of LED drivers out there, but one of the more interesting in recent memory came from ISSI in the form of a chip that turns I2C into a Charlieplexed LED array. You may have seen this chip — the IS31FL3731 — in the form of an Adafruit LED matrix and some stupid thing some idiot made, but with it you’re only ever going to get 144 LEDs in an array, not enough if you want real blinky bling.

Now ISSI has released a more capable chip that turns I2C into many more Charlieplexed LEDs. The IS31FL3741 will drive up to 351 LEDs in a 39×9 matrix, or if you’re really clever, an 18×18 single color LED matrix.

Features of this chip include reverse/short detection for each individual LED, 8-bit PWM, dimming functions, a de-ghosting feature that guarantees a LED is either on or off, a configurable row/column matrix, and a few other handy tools that you would like to see in a LED matrix driver chip. The most impressive chip in this series will be available for under $2/piece in quantities of 2500, although unlike the IS31FL3731, it appears this new chip will only be available in a QFN package.

Speaking from experience, this is a really great chip for driving a whole boatload of LEDs, provided you have a pick and place machine. Yes, you can hand-solder a QFN and several hundred 0402 LEDs, but I wouldn’t recommend it. I really, really wouldn’t recommend it. That said, this is the perfect chip for maximum blinky bling, and the press material from ISSI gives us the great idea of using one of these chips as the backlight controller for RGB LED mechanical keyboards. That’s a great application, and the chip is pretty cheap, too.

You can check out ISSI’s blinky demo video of this chip below.

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Coin-Sized LED Control

EE and firmware developer [Enrico] had played with LEDs as a kid, burning out his fair share of them by applying too much current. With the benefit of his firmware chops, he set about creating a board that drives LEDs properly.

[Enrico]’s project centers around a Texas Instruments LM3405 buck controller. It accepts input voltage from anywhere from 3V to 20V and outputs up to 20V/15W to one or more LEDs. He built a ton of safety features into it like short-circuit and open-circuit immunity, temperature control, and auto-off switching when idle. He also created a LED board to test the maximum efficiency of the driver. It consists of four Luxeon Rebel ES diodes, one each RGB and W. The entire back of the LED board is copper, with a monster heat sink attached.

You can follow along with the Glighter-S project on Hackaday.io, or you can buy one of his boards from his Tindie store.

We’ve covered LED drivers extensively in the past, with posts on a simple 10-watt LED driver and how to design your own LED driver.

Christmas Star uses Two AA Batteries

When [hkdcsf] was a teenager, he made a Christmas star with an up counter driving decoder logic and using transistors to light LEDs in festive patterns. He’s revisited this project using modern techniques including a microcontroller, a DC/DC converter, and constant current LED drivers.

The project uses two AA batteries, and that’s what makes the DC/DC converter necessary. Blue LEDs have a forward voltage of just over 3V, and the LED driver chip requires about 0.6V of overhead. Two fresh AAs will run a tad above 3V, but as they discharge, or if he’s using rechargeables, there just won’t be enough potential. To make sure the star works even with whatever LEDs are chosen, the converter takes the nominal 3V from the batteries and converts it to 3.71V.

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Homemade LED helmet

LEDHelmet

We’ve all seen Daft Punk helmet builds, but [George’s] project is a homemade LED helmet that takes no shortcuts and packs the visor full of hundreds of individual lights. He started with a prototype that uses a PIC 18F4580 microcontroller connected to a MAX7221 LED driver, which gave him control over some dot matrix displays to test the wiring and sample script. He then used this prototype setup to develop a scrolling text function.

With testing complete, [George] wired hundreds of LEDs into 8×8 block sections, using a cardboard jig to keep everything straight. He could have stopped there, but [George] took the build further, adding an LCD display and a 7-segment clock module to the inside of the helmet, in view of the wearer. The clock displays the helmet’s current beats per minute rate, while the LCD shows the content being displayed (pattern, text / Pacman, stripes). It’s possible to see out between the bottom of the display and the chin of the helmet. If you need better visibility we’d recommend a bike helmet matrix that isn’t as dense.

You can watch a video of the helmet running different patterns below. (Warning: music). When you’re done with that, why not LED all the things: from Infinity Mirrors to LED Sneakers.

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Another eerily similar high power LED driver hack

[Maximilian Güntner] dropped us a comment in last week’s globe writeup linking to his own project, which involves a similar high power LED driver mod. This looks like the exact same mod we came up with, and [Güntner] even used the mod to connect a bunch of high power LEDs to a PCA9685 LED driver [pdf]. It’s the same exact concept as Disco Planet!

It should come as no surprise that people have actually been modding high power led drivers in this way for some time. They are a few bucks per handful and take an enormous input voltage range. In [Güntner]’s case he grabbed a bunch of these from Dealextreme.  Actually there are two others on the site, and all three contain comments (dating back a year) with helpful tips on various ways to modify the little PCB.

Our Ebay sourced boards are different though. The boards [Güntner] purchased employ the PowTech PT4115 [pdf] which uses fewer parts and has an easy to follow data sheet. Take, for instance, the pin graciously labeled “DIM” with a little PWM signal next to it. The nerve! The Ebay drivers use the MCP34063 [pdf] which has a much more cryptic data sheet (burned two weeks and several notebook pages to figure out the circuit). Ultimately the two are so similar it makes no difference.

So, if you want to mod some LED drivers on your own, check out the how-to video after the jump. Thanks [mguentner]!

Continue reading “Another eerily similar high power LED driver hack”

Building a driver for absurdly high power LEDs

A few years ago, the highest power LEDs you could buy capped out around three watts. Now, LED manufacturers are taking things to ridiculous power ratings with 30, 40, and even 90 watt LEDs. Getting these high-power LEDs are no longer a problem, but powering them certainly is. [Thomas] built a LED driver capable of powering these gigantic LEDs and creating a light show that is probably bright enough to cause bit of eye damage.

[Thomas]’ LED driver is based on Linear Technology’s LT3518 LED driver. This driver is part of a project to build a huge WiFi controlled RGB LED, so the driver has outputs for three separate LEDs capable of sourcing 700 mA each.

Because [Thomas] is dealing with crazy amounts of heat and power required to light up these huge LEDs, the driver board features a temperature sensor next to each LED driver. When the board gets too hot, the driver automatically shuts down, preventing bad things from happening.

You can check out a few pictures of [Thomas]’ LED driver over on the build page for his WiFi LED project. A truly awesome amount of lighting power here, that also makes it impossible to get a good picture of the board in operation.