Advice About Over-Driving LEDs

December 3, 2013 by Mike Szczys 64 Comments

advice-about-overdriving-leds

We usually stay within the recommended Amperage with LEDs, but multiplexed displays provide an interesting opportunity to push them outside of that range. Because multiplexing scans a set of LEDs, they are not on all of the time. If your multiplexing setup allows you to remain within a certain time frame and duty cycle they can be driven past the constant current specifications. [Bryanduxbury] decided to take a look at the best way to overdrive LEDs.

The example that he gives is that his 30 mA constant current rated parts can accept up to 185 mA but only for 0.1ms with a duty cycle of 10%. If you know how to apply these figures you can get them to shine much brighter. This becomes especially useful when your multiplexed display already has the light off for the majority of the time because the resulting average luminosity will be much higher. His side-by-side test is shown above. With a current limited LED on the left of each color group, a multiplexed LED driven at normal voltage in the middle, and multiplexing with overdrive on the right.

The biggest drawback that [Bryan] mentions is that if your firmware hangs for more than the spec’ed time you’ll definitely fry these diodes.

Energy Harvesting Peltier Ring

December 2, 2013 by James Hobson 51 Comments

[Sean] is by no means an electrical engineer, but when he discovered the magic of Peltier plates he knew he had to make a project with them. This is his Energy Harvesting Peltier Ring.

The effect he is harnessing is called the SeeBeck Effect — the process of generating electricity through temperature differentials. He has shown how peltier plates work to many people, and, as you can guess, most people think they are amazing (free energy wow!). Unfortunately, most peltier plates are rather large and bulky, so [Sean] decided he wanted to try to design something small enough that could fit on a ring. Just a proof of concept, to light a tiny SMD LED.

The tiny Peltier plate he found generates about 0.3V with a temperature differential of about 20C — not bad, but it won’t light up any standard LEDs at that voltage! He started looking into voltage steppers and discovered Linear Technology’s 3108 Ultralow Voltage Step-up converter and Power Manager — a surface mount chip capable of scaling 0.3V to 5V. The only problem? [Sean’s] never done surface mount soldering.

His first circuit was built on a prototyping board, and after it worked successfully, he designed a PCB using Fritzing. Another success! Prototyping complete, it was now time to try to downsize the PCB even more to fit on a ring. Realizing there was no way he was going to fit it on a single ring, he decided to make a double ring out of CNC machined aluminum. He made use of his school’s CNC shop and the ring came out great. It works too! The room has to be fairly cool for the LED to light, but [Sean] definitely proved his concept. Now to make it even smaller!

Scratch-built Smart Flashlight

December 2, 2013 by Mike Szczys 13 Comments

scratch-built-smart-flashlight

This flashlight has a face; one of the many tricks which [Hobbyman] included during the development process. The smart flashlight build turned out to be a great way to practice so many different aspects of product development.

It was envisioned as a light for use when walking or biking that could do more than just light your way or flash on and off. Of course we know it’s really just a reason to spend way too much time in his lair. He started with the electronics, driven by a PIC 16F88. The 5×5 LED matrix gives him just enough to work with for patterns and rudimentary text. The prototype is wrapped up into a pretty tight package which leaves enough room in the 3D printed case for 4 AAA batteries. As the project progressed more and more features were added in. The most current offering includes a temperature sensor as well as the ability to react to ambient sound. See for yourself after the break.

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Arduino Christmas Lights

December 1, 2013 by James Hobson 12 Comments

Here’s a cool hack to get you in the December holiday mood! Arduino controlled Christmas lights!

It all started because [Anx2k] had some leftover LED’s from one of his other projects, so he decided to make use of them as permanently mounted Christmas lights. He’s installed them underneath his tiled roof, and run all the wires into his attic where he has an electrical box serving as the main control hub. He uses an Arduino Uno to control them, and a 460W computer power supply to provide the juice. The LED modules themselves are Adafruit RGB pixel strings. There’s actually three of the LED modules per tile — two shining up to illuminate the tile, and one shining out.

He’s set up a ton of different patterns to run, and they are pretty awesome! Check out the video after the break.

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RFID RGB Lamp Goes The Distance

November 29, 2013 by Mike Szczys 5 Comments

[Philippe Chrétien’s] project makes it to our front page just based on its completeness. When you hear about a multicolored lamp which changes based on an RFID tag you might not get too excited. When you look at the refined electronics and the quality of the wooden enclosure it’s another story entirely.

As we’ve said many times before, coming up with the idea for a project is the hardest part… especially when you just want to start hacking. With his kids in mind [Philippe] figured this would be something fun for them to play around with, opening the door to discussing the electronics concepts behind it.

He prototyped on a breadboard using three N-type MOSFETs to drive the colors of an RGB LED strip. The proven circuit was laid out and etched at home to arrive at the clean-looking Arduino shield shown off above. The entire thing gets a custom enclosure cut using layered plywood, a paper template, and a bandsaw.

Need a use for this once the novelty has worn off? Why not mod it to use as a motion activated night light? Alas the actual project link for that one is dead, but you get the idea.

Maglite 18650 Battery Conversion

November 28, 2013 by James Hobson 30 Comments

maglite 18650

Maglite’s used(?) to be the king of flashlights, but replacing those pesky D-cell batteries is kind of ridiculous in this day and age. So [Travis] decided to upgrade it to make use of the ever-so-common, 18650 lithium-ion battery.

Not looking to purchase any components [Travis] performed this hack using simple recycled household parts. You could solder tabs on the 18650’s so they better mimic a typical alkaline battery cell, but [Travis] notes that because most solder tarnishes the electrical conductivity isn’t always the greatest. So instead, he used aluminum foil. It doesn’t look professional, but it does the job and keeps all the components unmodified so the lithium cells can be used elsewhere if needed. To center the batteries inside the Maglite he used a few strips of cardboard from a case of beer — again, this is just making use of what was available. That being said however, if you wanted to do a professional job on it, nothing is stopping you! A 3D printed 18650 to D-cell adapter would look quite nice… Finally, in order to make the battery spring contact the smaller surface area of the lithium cells, all you have to do is flip it around backwards and slightly bend the inner spring out. That’s about it.

It’s a pretty simple hack we admit, but definitely super handy. In a past project [Travis] also replaced the halogen bulb with a high power LED, making this flashlight even more powerful — and because the LED driver accepts a broader range of voltages it lasts longer too. If you need more inspiration for retrofitting flashlights with LEDs check out this switch-mode driver board hack.

Unfortunately this hack does reduce the Maglite’s thief-head-bashing-ability with such light batteries.

Using DMA To Drive WS2812 LED Pixels

November 22, 2013 by Mike Szczys 17 Comments

It’s pretty well known by now that the LED pixel hardware which is starting to be commonplace, both WS2811 and WS2812, needs pretty strict timing in order to address them. There are libraries out there which mean almost no work on your part, but that’s no fun. [Elia] started looking into what it takes to drive the hardware, trying out a few 8-bit micros before moving to 32-bit with the help of an STM32VL Discovery Board. The move to a beefier processor brings a lot of speed, but why bit bang everything? He came up with a way to use the PWM and DMA features of the chip to drive the LEDs.

DMA is the Direct Memory Access unit that allows you to change the values being sent to the pixel without interrupting the processor. This is done by pre-loading the data at a memory location. This buffer is automatically read by the DMA unit — its values are used to set the PWM timer compare trigger in order to send out logic values show in the diagram above.

If you do want to delve further into this topic here’s a collection of techniques for driving the WS2811.

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