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A/D converter lines

This article explains how to use the A/D converter lines on your Acme board

The A/D converter input lines are available on the following pins:

Signal Description ARIETTA G25 ARIAG25 TERRA DAISY-1 FOXG20
3.3V 3.3 volt power line J4.5 D14.1 D4.1 J6.1
AVDD Clean 3.24V out for A/D circuitry D14.2 D4.2 J6.33
VREF A/D voltage reference input W19 D14.3 D4.3 J6.34
AGND Analog GND D14.4 D4.4 J6.35
AD0 Analog input 0 J4.34 W20 D14.5 D4.5 J6.30
AD1 Analog input 1 J4.36 W21 D14.6 D4.6 J6.29
AD2 Analog input 2 J4.38 W22 D14.7 D4.7 J6.28
AD3 Analog input 3 J4.40 W23 D14.8 D4.8 J6.27
GND Digital GND J4.9 W1 D14.10 D4.10 J6.40

VREF

On Arietta G25 the VREF line is wired internally to the 3V3 volt so is not possible to change it.

By wiring the VREF pin to AVDD or VDD (max 3.3 volt) it's possible to read a max voltage of 3.24 volt with a resolution of 10 bit (1024 samples). In this way the max sample resolution we obtain is about 3.24V/1024 ~= 3mV.

On VREF no voltage higher than 3.3 Volt can be applied. If you need to read a higher signal use a schematic like this:

A module called DAISY-20 is available to use these lines in the range of 0 to 10 volts. Elsewhere use this schematic to test quickly the A/D lines:

Using A/D converter input lines from user space

A detailed description of the Atmel AT91 ADC driver used on the Kernel 3.xx is available on this page:

The AT91 ADC driver uses the Industrial Input/Output (IIO) subsystem described here:

If you are using a Kernel version 2.x instead of 3.x follow this article: Using A/D converter input lines with Kernel 2.x.


DAISY-20 : Four channel A/D converter EURO 12.00

Front-end for the 4 channel A/D 10bits converter built-in the Atmel CPU.

Note: the daisy flat cable to wire this board is not included. Don't forget to buy it (code FLAT-20CM)

| Product description | Daisy catalog |


FLAT-20CM : 20cm flat cable with sockets for Daisy wiring EURO 3.00

20 cm ribbon cable with 10 wires compatible with the Acme Daisy Cabling System.

At least one of these cables is required to connect each Daisy module.

if you need different lengths please consider making your own the cable using the IDC socket JJ-02291-10P-F and the flat cable FC-3754-1M.




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