A Thousand LED Lights For Your Room

Sure, you could get a regular light fixture like a normal person… Or you could use close to a thousand RGB LEDs to light your room!

That’s what [Dmitry] decided to do after trying to figure out the best way to light his pad. You see, his room is 4 by 4 meters, and WS2812 RGB LED strips happen to come in 4 meter lengths… Coincidence? We think not.

The problem with using 16 meters of LED strips is powering them… You see, at 16 meters, you’re looking at about 5V @ 57.6A — and we’re guessing you probably don’t have a 5V 60A power supply handy. Not to mention if you run them in series, the resistance of the system is going to kill your efficiency and the last LEDs probably won’t even work… So [Dmitry] had to break the system up. He has two power supplies feeding the strips from the middle of each pair — that way, he doesn’t have to worry about any voltage drops due to the length of the strips.

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Stuffing Everything on a DIP32 Package

Putting an full microcontroller platform in a DIP format is nothing new – the Teensy does it, the Arduino nano does it, and a dozen other boards do it. [Alex] and [Alexey] aren’t content with just a simple microcontroller breakout board so they’re adding a radio, an OLED, an SD card reader, and even more RAM to the basic Arduino platform, all in a small, easy to use package.

The DIPDuino, as [Alex] and [Alexy] are calling it features an ATmega1284 processor. To this, they’re adding a 128×32 pixel OLED, a micro SD slot, and 1Mbit of SRAM. The microcontroller is a variant that includes a 2.4 GHz Zigbee radio that allows for wireless connections to other DIPDuinos.

What are [Alex] and [Alexey] going to do with their cool little board? They’re planning on using the OLED for a watch, improve their software so the firmware can be updated from the SD card, and one of [Alex]’s friends wants to build a RepRap controller with one of these. There’s a lot of potential with this board, and we’re interested in seeing where the guys take the project from here.

Android-based Reflow Brings Solder Profiles to Your Lab

[Andy Brown] is a prolific hacker and ends up building a lot of hardware. About a year back, he built a reflow oven controller. The board he designed used a large number of surface mount parts. This made it seem like a chicken or egg first problem. So he designed a new, easy to build, Android based reflow controller. The new version uses just one, easy to solder surface mount part. By putting in a cheap bluetooth module on the controller, he was able to write an app which could control the oven using any bluetooth enabled Android phone or tablet.

The single PCB is divided into the high voltage, mains powered section separated from the low power control electronics with cutout slots to take care of creepage issues. A BTA312-600B triac is used to switch the oven (load) on and off. The triac is controlled by a MOC3020M optically isolated triac driver, which in turn is driven by a micro controller via a transistor. The beefy 12Amp T0220 package triac is expected to get hot when switching the 1300W load, and [Andy] works through the math to show how he arrived at the heat sink selection. To ensure safety, he uses an isolated, fully encased step down transformer to provide power to the low voltage, control section. One of his requirements was to detect the zero cross over of the mains waveform. Using this signal allows him to turn on the triac for specific angle which can be varied by the micro controller depending on how much current the load requires. The rectified, but unfiltered ac signal is fed to the base of a transistor, which switches every time its base-emitter voltage threshold is reached.

For temperature measurement, [Andy] was using a type-k thermocouple and a Maxim MAX31855 thermocouple to digital converter. This part caused him quite some grief due to a bad production batch, and he found that out via the eevblog forum – eventually sorted out by ordering a replacement. Bluetooth functions are handled by the popular, and cheap, HC-06 module, which allows easy, automatic pairing. He prototyped the code on an ATmega328P, and then transferred it to an ATmega8 after optimising and whittling it down to under 7.5kb using the gcc optimiser. In order to make the board stand-alone, he also added a header for a cheap, Nokia 5110 display and a rotary encoder selector with switch. This allows local control without requiring an Android device.

Gerbers (zip file) for the board are available from his blog, and the ATmega code and Android app from his Github repo. The BoM list on his blog makes it easy to order out all the parts. In the hour long video after the break, [Andy] walks you through solder tip selection, tips for soldering SMD parts, the whole assembly process for the board and a demo. He then wraps it up by connecting the board to his oven, and showing it in action. He still needs to polish his PID tuning and algorithm, so add in your tips in the comments below.

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High Voltage AVR Programmer

The most common way of programming AVR microcontrollers is the In System Programming port. That little six-pin header with MOSIs and MISOs coming out of it will program every AVR you’ll ever come across. The ISP does have a downside – fuses. Set your fuses wrong, and without a High Voltage Serial Programmer, your chip is bricked. [Dilshan] designed his own HVSP that’s less expensive than the Atmel STK500 and has a nice GUI app.

Instead of following in the footsteps of the USBtinyISP, [Dilshan] is using a PIC18F as the main microcontroller in the programmer. This chip was chosen because of its built-in USB functionality. Because the High Voltage part of a HVSP operates at 12V, actually providing that voltage needed to be taken into consideration. For this, [Dilshan] is using standard 78xx regulators with an 18V input.

The app to control this programmer does everything you would expect, including all the usual AVRdude commands. A great build, and just what we need to reset the fuses on a few dozen chips we have sitting around.

DIY Electrical Body Fat Analyzer

Whether you are trying to drop some fat or build some muscle, it’s important to track progress. It’s easy enough to track your weight, but weight doesn’t tell the whole story. You might be burning fat but also building muscle, which can make it appear as though you aren’t losing weight at all. A more useful number is body fat percentage. Students from Cornell have developed their own version of an electrical body fat analyzer to help track body fat percentage.

Fat free body mass contains mostly water, whereas fat contains very little water. This means that if you were to pass an electrical current through a body, the overall bioelectrical impedance will vary depending on how much fat or water there is. This isn’t a perfect system, but it can give a rough approximation in a relatively easy way.

The students’ system places an electrode on one hand and another on the opposite foot. This provides the longest electrical path possible in the human body to allow for the most accurate measurement possible. An ATMega1284P is used to generate a 50kHz square wave signal. This signal is opto-isolated for user safety. Another stage of the circuit then uses this source signal to generate a 10ua current source at 50kHz. This is passed through a human body and fed back to the microcontroller for analysis.

The voltage reading is sent to a MATLAB script via serial. The user must also enter in their weight and age. The MATLAB script uses these numbers combined with the voltage reading to estimate the body fat percentage. In order to calibrate the system, the students measured the body fat of 12 of their peers using body fat calipers. They admit that their sample size is too small. All of the sample subjects are about 21 years old and have a similar body fat percentage. This means that their system is currently very accurate for people in this range, but likely less accurate for anyone else. Continue reading “DIY Electrical Body Fat Analyzer”

Prototyping With The ATMega1284P

While most people are moving onto ARMs and other high-spec microcontrollers, [Dave Cheney] is bucking the trend. Don’t worry, it’s for a good reason – he’s continuing work on one of those vintage CPU/microcontroller mashups that implement an entire vintage system in two chips.

While toying around with the project, he found the microcontroller he was using, the ATMega1284p, was actually pretty cool. It has eight times the RAM as the ever-popular 328p, and twice as much RAM as the ATMega2560p found in the Arduino Mega. With 128k of Flash, 4k of EEPROM, 32 IOs, and eight analog inputs, it really starts to look like the chip the Arduino should have been built around. Of course historical choices don’t matter, because [Dave] can just make his own 1284p prototyping board.

The board is laid out in Fritzing with just a few parts including a crystal, a few caps, an ISP connector, and pins for a serial connector. Not much, but that’s all you need for a prototyping board.

The bootloader is handled by [Maniacbug]’s Mighty 1284 Arduino Support Package. This only supports Arduino 1.0, not the newer 1.5 versions, but now [Dave] has a great little prototyping board that can be put together from perfboard and bare components in a few hours. It’s also a great tool to continue the development of [Dave]’s Apple I replica.

Reverse-Engineering a Superior Chinese Product

It makes an Arduino look like a 555.  A 364 Mhz, 32 bit processor. 8 MB RAM. GSM. Bluetooth. LCD controller. PWM. USB and dozens more. Smaller than a Zippo and thinner than corrugated cardboard. And here is the kicker: $3. So why isn’t everyone using it? They can’t.

Adoption would mandate tier after tier of hacks just to figure out what exact hardware is there. Try to buy one and find that suppliers close their doors to foreigners. Try to use one, and only hints of incomplete documentation will be found. Is the problem patents? No, not really.

[Bunnie] has dubbed the phenomenon “Gongkai”, a type of institutionalized, collaborative, infringementesque knowledge-exchange that occupies an IP equivalent of bartering. Not quite open source, not quite proprietary. Legally, this sharing is only grey-market on paper, but widespread and quasi-accepted in practice – even among the rights holders. [Bunnie] figures it is just the way business is done in the East and it is a way that is encouraging innovation by knocking down barriers to entry. Chinese startups can churn out gimmicky trash almost on whim, using hardware most of us could only dream about for a serious project.

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