Operation Manual

For sensing or feedback projects, the Gertboard’s ADC and DAC components are handy additions. Unlike the GPIO pins on
the Pi itself, which can only receive and send digital signals, the Gertboard includes two ADC and two DAC connections. The
ADC pins, located on the upper-left of the Gertboard, allow analogue components to be converted into digital signals compatible
with the Pi. As an example, Figure 13-10 shows how you can use the ADC pins to read the status of a potentiometer—a
component which varies its resistance according to the position of a slider or knob. This circuit could be used to control the Pi’s
volume in a media centre application, or to alter the speed of an attached motor. The DAC pins provide the opposite
functionality, taking a digital signal from the Pi and converting it to analogue. This could drive a speaker to create audio, or alter
the speed of a motor or the brightness of an LED.
For more complex projects, the Gertboard provides an open collector driver, which uses transistors to switch on and off devices
that have different power requirements to the 3.3 V used by the Gertboard or that draw a large amount of current and require an
external power supply to operate. The open collector driver can control the power supplies of up to six devices simultaneously
without requiring any hardware. This gives the Gertboard a large amount of flexibility—although transistors or relays can be used
with passive add-on boards like the Prototyping Pi Plate to achieve the same goal.
Figure 13-10: Connecting a potentiometer to the Gertboard’s ADC pins
Finally, the Gertboard provides access to a 28-pin microcontroller, which can be fitted to a socket located on the board itself.
When fitted, the Gertboard can be wired to address either the Raspberry Pi’s GPIO port or the microcontroller, or a
combination of the two. The Gertboard is designed to operate with an Atmel ATmega168 or ATmega328 microcontroller—the
same type of microcontroller used in the Arduino prototyping project. When fitted, you can write programs for the Gertboards’
ATmega microcontroller in the Atmel IDE, giving the Pi a useful level of compatibility with the wide array of existing ATmega-
targeted software available to download. It also gives the Pi the ability to address external hardware in a real-time manner, with
the microcontroller taking over responsibility for hardware interfacing and simply providing feedback to the Pi.
The Gertboard is a very advanced device, and isn’t suitable for every project. For many simple uses, a cheaper passive add-on
board like the Slice of Pi will usually be enough. However, for in-depth experimentation of just what is possible with the
Raspberry Pi’s BC2835 processor and/or to ensure that you’ll be able to interface almost any hardware with your Pi, it’s a great
choice and a powerful extension to the Pi’s already impressive abilities.
The Gertboard is available through Farnell at http://www.farnell.com/.