WiringPi supports a devLib module to allow you to use the Gertboard analog inputs and outputs.
The Gertboard is a buffered IO interface board for the Raspberry Pi with many features, LEDs, buffers and even an ATmega on-board. This expansion module deals with the 2-channel, 10-bit analog to digital converter and the 2-channel 8-bit digital to analog converter on-board.
#include <wiringPi.h> #include <gertboard.h>
gertboardAnalogSetup (int pinBase) ;
pinBase is the base pin that you want the analog ports to appear as. The setup routine allocates 2 pins and overlays the analog to digital input pins with the digital to analog output pins. So reading channel pinBase + 0 reads the first analog input channel (pin DA0 on the Gertboard), and writing pinBase + 0 outputs to the first analog output channel. (Pin AD0).
See the voltage.c and temperature.c programs in wiringPi/examples/Gertboard directory for examples of use.
- The analog interface chips on the Gertboard are connected to the SPI bus. You need to load the SPI kernel modules with gpio load spi and make sure that the 5 SPI jumpers are in-place on the Gertboard – pins SCLK, MOSI, MISO, CSnA and CSnB.
- The analog to digital convertor is a 10-bit device. Values returned will be in the range 0-1023 representing an input voltage of 0 to 3.3 volts.
- Input Voltage calculation: volts = analogIn * 3.3 / 1023
- The digital to analog converter is an 8-bit device. Values sent to it should be in the range 0-255 representing an output voltage on 0 to 2.047 volts.
- Output voltage calculation: volts = analogOut / 255 * 2.047
- The gpio program has commands to directly read and write the analog ports on the Gertboard: gpio gbr 0 will read input channel 0, gpio gbw 1 55 will write the value 55 output channel 1.