Overview

The Analog Shield offers a high fidelity and easy way to connect your Arduino™ or chipKIT™ to analog circuits. In order to do this, the Digilent Analog Shield* provides:

Figure 1. The Analog Shield.

• 4 Channel, 16 bit 100 ks/s SARADC.
• 4 Channel 16 bit 100 ks/s stringDAC.
• Variable +/-7.5V Supply.
• Fixed +/-5V Supply.
• A small breadboard.
• Software read and write to theADC/DACwith a single line of C.

In addition to providing many of the features available on other prototyping or breadboard shields, this shield provides substantially more sensitive inputs and outputs than the Arduino Uno™ or the chipKIT UNO32™, as well as providing the bipolar inputs and power supplies needed to drive many useful analog circuits. The Analog Shield communicates with the Arduino using the SPI communication protocol. The Analog-to-Digital input converter (ADC) and Digital-to-Analog output converter (DAC) both use the standard Arduino form factor SPI bus pins and use independent chip selects.

The Analog Shield allows better resolution for smaller and more sensitive signals that cannot reliably be recorded or generated using the standard pins on the Arduino. A few demos using the Analog Shield have been developed: Sine wave / function generator (using direct digital synthesis). FFT spectrum analyzer. Polyphonic Music generation. 4-channel low bandwidth oscilloscope. Lissajou diagram generator. XY-Analog scope display driver.

These demos are each explained in their own associated documentation.

Figure 2. The analog shield with Hardware callouts.

The 2×4 header has the fourADCchannels and four pins for the common ground on the board. The 4 ground pins are on the outside row of the header, while the 4ADCchannels are on the inner row of the header. TheADCcan read 4-channels of data at 16-bits per channel using the analog.read() function, which are labeled with A0- A3. For more detail on the op-amp circuitry ahead of theADC, please refer to the shield schematic.

The 2×4 header has the fourDACchannels and four pins for the common ground on the board. The 4 ground pins are on the outside row of the header, while the 4DACchannels are on the inner row of the header. TheDACmodifies the analog signal produced from an Arduino or chipKIT. The standard Arduino/chipKIT analogWrite() function produces a pulse-width modulated (PWM) square wave that approximates the desired overall value over time. PWM is acceptable for many applications, like dimming anLEDor driving a motor, but it is not adequate for more sensitive analog circuits. Once a value is set to aDACchannel, the channel will produce a steady voltage corresponding to the provided value. Setting values on the channels is facilitated with the analog.write() function, and the channels are labeled D0-D4. For more detail on the op-amp circuitry behind theDAC, please refer to the shield schematic.

The 2×5 header has a positive 5V rail, a negative 5V rail, a positive variable voltage rail, a negative voltage rail, 2.5V reference voltage rail, and five pins for the common ground on the board. The 5 ground pins are on the outside row of the header while the 5 power supplies are on the inner row of the header. The +/-5V rail can vary due to USB power specification. The +/-Vadj rails can be adjusted using the variable voltage potentiometer located at the lower right corner of the shield. Adjusting the potentiometer will change the voltages of the +/-Vadj rails. There is also a +2.5V rail to be used as a reference voltage.

The jumper needs to be set for whether the connected board uses IOREF, 3V3, or 5V0 for the I/O for the SPI interface.

The potentiometer is can be used to adjust the +/-VADJ power supply rails.

包含在模拟盾是一个简单的图书馆y that is built to optimize readability and performance. It attempts to provide a similar interface to the standard Analog read and write functionality already present in the IDE. Instructions on installing the library are included in the library folder and in the “Analog Shield – 02 First Time Setup” document. After successfully installing the library into the IDE, the library can be invoked with the command:

#include 

Once the analogShield library is included, a class variable called analog will be accessible. The analog variable will allow access to the analogShield library functions.

To sample one of the analog input channels, use the function below. read() returns the voltage read on the channel. The voltage is returned in a binary representation from 0 to 65535 for -5V to 5V.

unsignedintread(intchannel,bool mode=false);

To read from channel 0 (without differential mode) the syntax will look like this:

unsignedintdata;data=analog.read(0);

该方法样品选择的模拟输入。“莫de’ is an optional parameter. False (the default value) is the normal, single-ended mode where each analog pin is referenced to ground. True enables ‘differential’ mode, where the value returned is the difference between the voltages on pairs of adjacent inputs (i.e., A0-A1 and A2-A3). signedRead() acts the same at read() but returns a signed integer.

signedRead(intchannel,bool mode=false);

To read from channel 0 (without differential mode) the syntax will look like this:

intdata;data=analog.read(0);

To write data to theDAC, there is a function called write(). This function allows the user to write to any channel: channel 0 and 1; channel 0, 1, and 2; or channel 0, 1, 2, and 3.

write(intchannel,unsignedintvalue);write(unsignedintvalue0,unsignedintvalue1,bool mode);write(unsignedintvalue0,unsignedintvalue1,unsignedintvalue2,bool mode);write(unsignedintvalue0,unsignedintvalue1,unsignedintvalue2,unsignedintvalue3,bool mode);

To write a value just for channel 1, the syntax will look like this:

unsignedintdata=65535;analog.write(1,data);

To write multiple values to channels 0, 1, and 2 and have them update at the same:

unsignedintdata0=65535;unsignedintdata1=256;unsignedintdata2=0;analog.write(data0,data1,data2,true);

Simultaneously updating methods are useful for higher speed applications where a small delay between channel outputs will produce unwanted signals or timing issues. For example, to use the shield to drive the X-Y input of an oscilloscope to draw a circle, a delay between writing the X and the Y channels produces a ghost ‘ellipse’ drawn during the interim between the X and YDACupdates. This is a simple but powerful library to help the user get started. It is well documented to ease modification of the library for any individual project. The power supply is entirely analog, and as such, needs no software to operate. However, theDAC(part number DAC8564) andADC(part number ADS8343) are both SPI devices. Their datasheets are freely available on the manufacturer’s webpage.

Unlike the native analog input of the Arduino, the Analog Shield provides a 16 bitADC, (as opposed to 10bits provided by the Arduino UNO and the ChipKIT UNO32) offering greater precision (about 25dB) than the Arduino or chipKIT. Additionally, theADCworks as a bipolar input, meaning that sense signals in the range of +/-5V can be sensed without any additional hardware. The onboardDACprovides a similar improvement in precision. The Analog Shield provides 16 bits of precision, and offers as much as 25dB better signal-to-noise ratio when driving a sinusoidal output at low frequency. The Analog Shield provides a compact integrated power supply with fixed and adjustable outputs to allow a variety of analog circuits to be assembled with a minimum of wasted space and complexity. Special thanks to Gregory Kovacs, Fernando Mujica, Clint Cole, and their respective teams at Stanford, TI, and Digilent for supporting this project to its completion!