AD7367

Arduino library for the AD7367, 2 channel simultaneous sampling 14 bit ADC.

Description

Experimental

The AD7367 is a device with two ADC's which can sample 2 channels simultaneously at 14 bits with a theoretical speed of up to 1 MSPS. The AD7366 is a similar 12 bits device. The two samples can be clocked out (SPI alike) simultaneous over two data pins.

This library implements the basic functionality to trigger a measurement and read the bits of the two ADC's over two data pins. It is a software (bit bang) solution which might be called a Dual-SPI or DSPI, to read the two "MISO" lines in parallel.

Warning The library is not tested with hardware yet.

Feedback, issues, improvements are welcome. Please file an issue on GitHub.

QSPI - 4 lines

There exists a QSPI (quad-SPI) protocol to sample up to 4 "MISO" lines in parallel. This is mostly used to clock out a byte (8 bits) as two nibbles (4 bits). In theory this QSPI could be used to sample the two data channels of the AD7367. It would have to ignore 2 of the 4 "MISO" channels. In practice this is inefficient and thus far never seen QSPI-Arduino working.

SPI - single line

According to the datasheet it is possible to read both ADC's over one "MISO" line thus with standard SPI. After clocking out the ADC-a1, if one continues clocking the data from the other ADC-b1 comes over the same line. Drawback is that the clocking takes about twice as long and one needs some bit-manipulation to split the data. Effectively one looses about 50% of the performance. And that "parallel" performance is a core strength of this AD7367.

Configuration wise it is easier to have two single ADC's side by side if performance is not a requirement. Note the library does not implement this single SPI feature.

Related

• https://github.com/RobTillaart/AD7367 simultaneous sampling 14 bit ADC.
• https://github.com/RobTillaart/AD7367_SPI consecutive sampling 14 bit ADC.
• https://github.com/RobTillaart/ADC081S 10-12 bit, single channel ADC
• https://github.com/RobTillaart/ADC08XS 10-12 bit, 2 + 4 channel ADC
• https://gammon.com.au/adc tutorial about ADC's (UNO specific)
• https://github.com/RobTillaart/MCP_ADC 10-12 bit, 1,2,4,8 channel ADC
• https://github.com/RobTillaart/ADS1x15 12 & 16 bit ADC, I2C, slow
• https://github.com/RobTillaart/PCF8591 8 bit single ADC (+ 1 bit DAC)

Forum link where it all started

• https://forum.arduino.cc/t/request-for-ad7367-library-for-arduino/1340710

Interface

#include "AD7367.h"

Constructor

• AD7367(uint8_t select, uint8_t clock, uint8_t convert, uint8_t busy, uint8_t data0, uint8_t data1)
• AD7366(uint8_t select, uint8_t clock, uint8_t convert, uint8_t busy, uint8_t data0, uint8_t data1)

pin	IO	description
select	OUTPUT	Chip select
clock	OUTPUT	Serial clock
convert	OUTPUT	start conversion
busy	INPUT	conversion busy
data0	INPUT	Serial data ADC A
data1	INPUT	Serial data ADC B

• void begin() initializes internal state.
• uint8_t getType() returns 67 or 66, depends on type (which constructor used)
• int getBits() returns resolution 12 or 14 bits, depends on type.

Read

• int read() synchronous call to make a measurement from both ADC-A and ADC-B. These values are stored in an internal buffer to be fetched with getLastADCA() and getLastADCB(). Note the ADDR line below determines which lines are read (a1, b1) or (a2, b2). Actually it is a wrapper around the next three calls.
• void triggerConversion() asynchronous call to start ADC measurements.
• bool conversionBusy() returns true when the measurement are ongoing.
• bool conversionReady() returns true when the measurement are ready.
• int readAsync() clocks in the data from the two ADC's of the device. Should be called only when the measurements are ready.
• int getLastADCA() returns the last measurement of ADC-A Multiple calls to getLastADCA() will result in the same value until new data is read, either synchronous or asynchronous.
• int getLastADCB() returns the last measurement of ADC-A Multiple calls to getLastADCB() will result in the same value until new data is read, either synchronous or asynchronous.

The device has an option to read both measurements using only one data pin however this is not supported. See SPI - single line section at the top.

FastRead

• int fastRead(int &a, int &b) reads and returns two measurements by reference. This function is more ideal e.g. to fill an array. See example. Note the ADDR line below determines which lines are read (a1, b1) or (a2, b2).

RANGE

Datasheet page 16, 17, table 8

• void setRangePin(uint8_t range0, uint8_t range1) define the two range pins.
• int setRange(uint8_t range) set range to 0, 1 or 2 see table below. One should not set a range outside these values and one cannot change the range when conversion is busy.
• uint8_t getRange() returns the set range or 255 if pins are not set.

range	RANGE1	RANGE0	selection	notes
0	LOW	LOW	±10 Volt
1	LOW	HIGH	±5 Volt
2	HIGH	LOW	0 to 10 V
other	-	-	NOT ALLOWED!	setRange() returns -1

Instead of setting the RANGE pins, one can hardwire these pins.

DATASHEET WARNING do not set both range pins to HIGH.
(not clear what will happen, expect broken device)

DATASHEET WARNING do not change the range when conversion is busy. setRange() returns -2 when busy. (not clear what will happen)

ADDR

Datasheet page 17

• void setADDRpin(uint8_t pin) define the ADDR pin, default LOW = (Va1, Vb1).
• void ADDRwrite(uint8_t mode) LOW = (Va1, Vb1) or HIGH = (Va2, Vb2) input pins in the read() or fastRead() function.

Instead of setting the ADDR pin, one can hardwire this pin.

REFSEL

Datasheet page 19

• void setREFSELpin(uint8_t pin) define the REFSEL pin, default HIGH = internal.
• void REFSELwrite(uint8_t mode) LOW = external voltage or LOW = internal 2.5 Volt.

Instead of setting the REFSEL pin, one can hardwire this pin.

Obsolete

• int getValue(channel) replaced by int getLastADCA() and int getLastADCB().

Future

Must

• read the datasheet
• improve documentation
• get hardware to test the library

Should

• add examples

Could

• addint getMaxValue() 12 bit == 4095, 14 bit = 16383.
• add float getVoltageA()
• add float getVoltageB()
• optimize code.
  • digitalPulse(pin) LOW_HIGH
• optimize AVR with registers a la SW SPI.
• error handling?
• interrupt example?
• add enum for RANGE AD7367_RANGE_PM10 PM5 0T10
• add enum for REFSEL
• add enum for ADDR ?

Wont

• HW SPI won't work as there are 2 data channel.
  • one could sample both ADC over 1 channel with 2x clock pulses (fig 28)
• SPI 4 or QSPI might be an option?

Support

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Thank you,