We organized a great hackathon on 22nd January 2014 in Otaniemi.
The Ell-i hackathon day started with Pekka telling us what Ell-i is all about, the current state of the Ell-i boards and our goals. Teemu followed by explaining the structure and operation of what we were going to build: a simple DC-DC buck converter.
Every group got an Ell-i board, a power over ethernet injector for powering the Ell-i board, a breadboard shield, and a bunch of components. The first task was to install the development environment for Ell-i boards. It is a slightly modified version of the standard Arduino IDE, modified to support the custom Ell-i runtime. Connection of a led, a resistor, and compiling the basic Arduino blink sketch proved that the setup was working.
The real goal of the day was this simple buck converter circuit:
Not a particularly efficient or a high power circuit, but designed for demo use. It has a low component count, and all components are suitable for breadboarding. The circuit is able to convert from the 48 VDC coming from the PoE supply to a constant current driving a power led. The switch of this converter is driven by a PWM signal from the Ell-i board. By the way, arduinistas: this circuit does not work with an Arduino. In an Ell-i board, the frequency of the PWM controlled by the analogWrite() function is 50 kHz, not the measly 500 Hz of standard arduinos! That is high enough to be usable for controlling the switch of a DC-DC converter.
In some groups, the circuit was quicky completed; in others, much headscratching ensued. Having two instructors roving around answering questions worked perfectly – all groups got their converter done at some point of the day. My group made the power led to fade in and out in a couple of different ways, and flash out some morse code. Quite easy, once the buck was working.
One group had brought their own set of components, including a bit better coils capable of handling more power, and an awesome ouch-my-eyes-hurt power led — with 50W rating! They managed to get roughly 30 watts from the PoE port through their breadboarded buck converter and into the led. That was so much that they had to keep the led covered to prevent the ouch-my-eyes-hurt thing from happening.
The most delighting thing about the day was that everything went smoothly. We had no major problems, no fire or escaped smoke. A very educational day all in all! Thanks everybody for participating, we rock!
All materials are available at GitHub, if you want to take a look.
More photos are available here.
The hackathon was organized at the EIT ICT Labs in Otaniemi. ELL-i is a member of EIT ICT Labs Business Development Accelerator and supported by EIT ICT Labs.