Extended ADC Shield User Manual
Contents
1. Arduino application 2 Begin with a demo a File gt Examples gt ExtendedADCShield gt Examples gt choose one of the following demos i ExtendedADCShieldDemo an example of how to use the shield for a variety of analog inputs communicating with the shield over the Arduino s built in SPI ii ExtendedADCShield100KHz an example of how to achieve 100kHz sampling rate on a single input 3 Add the ExtendedADCShield library to an existing sketch a Sketch gt Import Library gt ExtendedADCShield b See the function reference below ExtendedADCShield Library Function Reference ExtendedADCShield byte number_bits Description Use this to create an instance of the ExtendedADCShield library Parameters number_bits the number of bits that the analog to digital converter IC on the shield is capable of Use 12 for the LTC1857 14 for the LTC1858 or 16 for the LTC1859 Return Value None ExtendedADCShield byte CONVST byte RD byte BUSY byte number_bits Description Create an instance of the ExtendedADCShield library with user defined pins Parameters CONVST the Arduino pin number connected to the shield s CONVST input RD the Arduino pin number connected to the shield s RD input BUSY the Arduino pin number connected to the shield s BUSY output number_bits the number of bits that the analog to digital converter IC on the shield is capable of Use 12 for the LTC1857 14 for the LTC 1858 or 16 f2. the shield is pulled low while the onboard ADC is performing a conversion immediately after the CONVST pin is pulled high by the Arduino The maximum conversion time for the ADC is 5us which is shorter than the time it takes an Arduino Uno to toggle the CONVST line high and then back low Therefore when a 2015 Mayhew Labs Contact CustomerService ma yhewlabs com 2 Extended ADC Shield Mayhew Labs User Manual conversion is triggered by the Arduino the conversion is complete before the BUSY line can be checked to see whether the ADC conversion is finished This means that the BUSY line is not needed since the conversion result will always be ready by the time the Arduino asks for it This is the case for 16 MHz Arduinos but not true for those running at a faster clock speed like the Due Therefore you cannot free up this pin on Arduinos running faster than 16 MHz The ExtendedADCShield library was written to cover all Arduinos and therefore has a wait loop to check when the BUSY line goes high If you wish to free up Pin 9 so that is not used for the BUSY signal you must do two things 1 remove the solder jumper from SJ6 on the back of the shield and 2 comment out the following lines from the file ExtendedADCShield cpp in the library pinMode _BUSY INPUT in two places while digitalRead _BUSY LOW Installing Input Filtering Capacitors If you need to smooth out noise on the incoming analog signals you may populate capa
3. Extended ADC Shield Mayhew Labs User Manual Table of Contents Introduction Hardware Description Pin Descriptions Setting the SPI communication level Setting User Defined pin usage Freeing Up Pin 9 BUSY Installing Input Filtering Capacitors Extended ADC Shield Schematic ExtendedADCShield Library for Arduino RWWNNNDNDP Introduction The Extended ADC Shield gives your Arduino the ability to measure extended voltage ranges with higher resolution and faster speed than the built in analog to digital converters ADCs Each of the eight input channels can be configured as a single ended ground referenced or differential input and can be set for an input range of OV to 5V OV to 10V 5V and 10V Analog signals are connected to the shield using robust screw terminal connections and are safe for input voltages up to 25V The shield is available in 12 bit 14 bit and 16 bit versions and has a maximum sample rate of 100ksps regardless of which version is used The shield interfaces with any Arduino hardware platform over SPI along with a few additional control signals and has selectable pin usage for these signals The shield can be set to communicate at 5V or 3 3V levels making it safe for 3 3V tolerant Arduinos This manual will help you get up and running and also explain how the shield works If you want to skip the details and get down to business install the library and run the demo examples see the ExtendedADCShield Library
4. Value the voltage of the last configured analog input at the time this function is called analogReadConfigNext example Read input 0 set up input 1 as single ended unipoloar 0 to 5V Assumes that input 0 was configured previously ch0 extendedADCShield analogReadConfigNext 1 SINGLE_ENDED UNIPOLAR RANGED5V 2015 Mayhew Labs Contact CustomerService mayhewlabs com 5
5. citor positions C1 through C12 on the shield with 0603 sized capacitors The LTC185x datasheet recommends a 3000pF NPO type capacitor in order to minimize wideband noise The capacitors that should be placed depend on whether you are using single ended inputs or differential inputs See the table below for which capacitor positions to use and the image for capacitor orientation Single Ended Capacitor ry Input Channel _ Position E 0 C1 F BO 1 C3 2 C4 3 C6 4 C7 5 c9 6 C10 7 C12 Differential Capacitor Input Channel Position 0 1 C2 2 3 C5 4 5 C8 6 7 C11 Extended ADC Shield Schematic The schematic for the shield can be found here 2015 Mayhew Labs Contact CustomerService ma yhewlabs com 3 Extended ADC Shield Mayhew Labs User Manual ExtendedADCShield Library for Arduino The ExtendedADCShield library was created to make initializing and controlling the shield easier It hides the SPI message setup and communication along with toggling of the extra control lines How to install the library 1 Quit the Arduino application if it s running 2 Download ExtendedADCShield zip and unzip it 3 Move the ExtendedADCShield folder to your Arduino libraries folder a Windows My Documents Arduino libraries b Mac Documents Arduino libraries c Linux the libraries folder in your sketchbook 4 Restart the Arduino application How to Use the library 1 Start the
6. e shield sets the voltage swing of the shield s output pins SDO and BUSY If you are using a 3 3V tolerant Arduino variant like the Due set this solder jumper as shown on the back of the board using a small bead of solder that connects the center pad to the right pad Please note that although SPI communication at 3 3V is possible the shield must be powered from a 5V supply Setting User Defined pin usage If you wish to use different pins than those listed above for SPI communication for example a different digital pin for RD slave select you can do so using solder jumpers SJ1 through SJ6 and P5 on the shield If you remove the solder bead from these solder jumpers you can run wires from any Arduino pin or external control directly to the ADC IC s inputs using the connections at P5 This is useful if you have multiple devices communicating on the same SPI bus and you need to have a different slave select line controlling this shield A special initialization function exists in the ExtendedADCShield library for changing which Arduino pin is used for CONVST RD and BUSY The jumpers are also useful if you want to communicate with the shield using software SPI bit banging A helpful tutorial on SPI bit banging can be found here Bit banging mode is not supported by the ExtendedADCShield library so read the LTC175x datasheet for more information on manually sending commands to the shield Freeing Up Pin 9 BUSY The BUSY output line from
7. for Arduino section Hardware Description The Extended ADC Shield uses the Linear Technology LTC185x series of 8 channel analog to digital converter ICs which include the LTC1857 12 bit LTC1858 14 bit and LTC 1859 16 bit These are unique ADCs because each channel may be software configured for different input ranges and be programmed for single ended or differential inputs and combinations of both while being powered from a 5V supply The IC s are also 5V and 3 3V communication level compatible making them ideal ADCs for all Arduino hardware platforms The shield is set up to have flexible configuration for what Arduino pins it occupies It uses the Arduino s ICSP header for SPI communication so that it can communicate with all Arduino variants The shield uses isolated analog and digital ground planes so that noise from switching communication lines can be kept to a minimum on the analog inputs It also contains positions for 0603 sized capacitors that the user can populate to help filter out incoming noise both on single ended and differential inputs 2015 Mayhew Labs Contact CustomerService ma yhewlabs com 1 Extended ADC Shield Mayhew Labs User Manual Pin Descriptions Name Pin Description CONVST 108 or user Conversion start Pull this pin high for at least 40ns to start an analog to digital defined conversion on the last configured channel 1010 or user Read Slave select Pull this pin lo
8. or the LTC1859 Return Value None 2015 Mayhew Labs Contact CustomerService ma yhewlabs com 4 Extended ADC Shield User Manual Mayhew Labs float analogReadConfigNext byte channel byte sgl_diff byte uni_bipolar byte range Description Reads the last configured analog input sets up the configuration of the next analog input Note that the inputs to this function are used to set up the next analog input to read while the output is the value of the last configured analog input at the time this function is called See the example below for reference Parameters channel the channel 1 to 7 that you want to configure next For differential analog inputs set this to be the positive input channel of the differential pair The differential pairs are 0 1 2 3 4 5 and 6 7 For example if you want the value of input 7 minus input 6 set channel to be 7 sgl_diff set whether the next configured channel should be single ended a single input pin or differential one input minus another input using one of the following values SINGLE ENDED DIFFERENTIAL uni_bipolar set whether the next channel to configure should be unipolar 0 to 5V and 0 to 10V or bipolar 5 to 5V and 10 to 10V using one the following values UNIPOLAR BIPOLAR range set whether the next channel to configure should be 5V and 5 to 5V or 10V and 10 to 10V using one of the following values RANGES5V RANGE10V Return
9. w when you want to communicate to the RD SS defined shield This pin doesn t need to be low to initiate a conversion via the CONVST pin SPI clock Data clock to the shield from the Arduino Data is clocked in or out SCK ICSP pin3 or on the rising edge On Uno or Duemilanove this is connected to 1013 On user defined Mega1280 or Mega2560 this is connected to 1052 On Leonardo or Due it is not connected to any IO pins ICSP pin 4 or SPI data input Data input to the shield from the Arduino On Uno or SDI ser defined Duemilanove this is connected to 1011 On Mega1280 or Mega2560 this is connected to 1051 On Leonardo or Due it is not connected to any IO pins ICSP pin 1 or SPI data output Data output from the shield to the Arduino On Uno or SDO lider defined Duemilanove this is connected to 1012 On Mega1280 or Mega2560 this is connected to 1050 On Leonardo or Due it is not connected to any IO pins Busy Pulled low when an analog to digital conversion is in progress BUSY IO9 or user immediately after the CONVST pin is pulled high The maximum conversion defined time is 5us This pin can be freed up so that the shield no longer uses it See details below Setting the SPI communication level The shield can communicate over SPI at both 5V and 3 3V levels The input pins CONVST RD SCK SDI have a high level input threshold of 2 4V and are therefore compatible with all Arduino variants The SPI COM LEVEL solder jumper on the back of th
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