Hardware

Hardware

eHZy uses Arduino as a platform to build the mobile device. The schematics and the source code are provided here, but if you want to use eHZy, you will probably have to build the device for yourself (or find someone who will do it for you). It isn't too hard, though - if you're able to solder together the average blinking kit, building this device should be well within your skills.

Schematics

The schematics are actually rather simple - it's a simplified version of the IR interface used by the volkszaehler.org project. I'd like to thank Udo for helping me out with the circuit design.

Part List

This device uses the Arduino Uno as a basis and a Wireless SD Shield as an extension. The latter provides both an SD card holder as well as a prototyping area where the additional circuit can be built easily.

Part	Cost (approx.)
Arduino Uno	25 €
Arduino Wireless SD Shield	25 €
Arduino Box	12 €
1 Transistor BC337-40	0.08 €
1 Photo Transistor SFH309FA	0.70 €
1 Piezo Speaker (e. g. PES 21N30P)	2.50 €
1 Resistor 220 Ohms
2 Resistors 15k Ohms
9V Battery Clip
several pieces of wire
clip or rubber plug to mount the photo transistor

Caution: Make sure that you get a piezo speaker, not a piezo buzzer (which is essentially a piezo speaker with a built-in tone generator)!

Assembly

It is strongly recommended to try the entire setup on a breadboard first before soldering everything together. While the additional components are rather cheap, the wireless shield isn't.

Here is one way to place the components on the wireless shield. You may have to adapt this if your piezo speaker is of a different shape or size. The green lines are wire connections that have to be made on the upper side of the shield while the thick grey lines are soldered connections at the bottom of the shield.

This is what the circuit might look like after it's been put together:

The photo transistor can be placed anywhere on the box - here is an example.

Don't forget to put an Arduino sticker on the box :-)

Firmware

The source code can be found in the git repository, master branch, folder arduino. You can either download it from here or checkout the entire code repository.