The EAUduino was inspired by the need for a time-sensitive controller for relays that would react to temperature. As a result, its adjunct circuitry reflects that purpose.

• Dallas Semiconductor DS1337+ Real-Time Clock. This clock is powered by a battery (anything 6V or greater). The DS1337+, unlike some similar chips in the series, is capable of generating an interrupt on alarm. This is an I²C device that uses Arduino analog pins 4&5, and the interrupt line is tied to Arduino digital pin 0. The circuit for this on the Eauduino board features a 32.768Khz clock crystal, decoupling and supply capacitors, a power-efficient low-dropout (LDO) regulator and a 9V battery clip. The DS1337+ can be powered via the LDO regulator with any voltage between 5.5V and 12V, so if you don't like using a 9V battery you have a great deal of flexibility.

• A ULN2803A driver chip configured for 5V at up to 500ma for driving relays or other control elements. Arduino digital lines D9, D10, D11 and D12 need to be configured as outputs, and control the outputs of the ULN2803A. The driver outputs are accessible via polarized connectors, and four 11" plugs are supplied for maximum flexibility.

• A 74HC14N inverting Schmitt trigger configured for Arduino digital lines D1, D2 and D3. These lines can only be used as inputs in the EAUduino. D1 can be used to trigger external interrupts. A Schmitt trigger brings a certain amount of noise immunity to input circuits, which is very beneficial when the output is likely to be switching high voltages and currents. In addition, due to the propagation delay of the Schmitt trigger, it effectively de-bounces the signal thereby making it unnecessary to include de-bouncing code in the software. By using an inverting Schmitt trigger combined with weak pull-up resistors, a positive logic is sent by connecting the input to ground. These inputs, along with matching ground pins, are brought out into a standard connector for easy accessibility.

Beyond these circuits, the EAUduino has the following benefits that are common to other Freeduino implementations:

1. It can be conveniently programmed from the standard Arduino IDE. The EAUduino has been tested with version 11 and version 12 on both Linux and Windows XP.

2. Like the Modern Devices Bare Bones Board, the Sanguino and many other Freeduinos, the EAUduino is programmed via an inexpensive USB to TTL serial cable that is purchased once and then used for many different boards. This saves the cost of including such a converter on each board, thereby making it less expensive to deploy.

3. I/O lines that aren't used for communication with the DS1337, ULN2803A or 74HC14N are available in two banks for analog and digital. Instead of making these I/O lines available via only a single pin, the EAUduino presents them in the standard 3-pin servo format compatible with widely available 3-pin servo control cables. This gives maximum flexibility for off-board circuitry. I/O line D13 is tied to an LED for experimentation and I/O line D4 is unavailable.