NAME
RPi::ADC::ADS - Interface to ADS 1xxx series analog to digital
converters (ADC) on Raspberry Pi
SYNOPSIS
use RPi::ADC::ADS;
# instantiation of the object, shown with optional parameters
# with their defaults if you don't specify them
my $adc = RPi::ADC::ADS->new(
model => 'ADS1015',
addr => 0x48,
device => '/dev/i2c-1',
channel => 0,
gain => 1,
mode => 1,
rate => 0,
polarity => 0,
queue => 3,
);
my $volts = $adc->volts;
my $percent = $adc->percent;
my $int = $adc->raw;
# all retrieval methods allow you to specify the channel (0..3) in the call
# instead of using the default, or the one set in new()
my $percent = $adc->percent(3);
...
DESCRIPTION
Perl interface to the Texas Instruments/Adafruit ADS 1xxx series Analog
to Digital Converters (ADC) on the Raspberry Pi.
Provides access via the i2c bus to all four input channels on each ADC,
while performing correct bit-shifting between the 12-bit and 16-bit
resolution on the differing models.
PHYSICAL SETUP
List of pinout connections between the ADC and the Raspberry Pi.
ADC Pi
-----------
VDD Vcc
GND Gnd
SCL SCL
SDA SDA
ADDR Gnd (see below for more info)
ALRT NC (no connect)
Pinouts `A0' through `A3' on the ADC are the analog pins used to connect
to external peripherals (specified in this software as `0' through `3').
The `ADDR' pin specifies the memory address of the ADC unit. Four ADCs
can be connected to the i2c bus at any one time. By default, this
software uses address `0x48', which is the address when the `ADDR' pin
is connected to `Gnd' on the Raspberry Pi. Here are the addresses for
the four Pi pins:
Pin Address
---------------
Gnd 0x48
VDD 0x49
SDA 0x4A
SCL 0x4B
OBJECT METHODS
new
Instantiates a new RPi::ADC::ADS object. All parameters are optional,
and are all sent in as a single hash.
Parameters:
model => $string
Optional. The model number of the ADC. If not specified, we use
`ADS1015'. Models that start with `ADS11' have 16-bit accuracy
resolution, and models that start with `ADS10' have 12-bit resolution.
addr => $hex
Optional. The hex location of the ADC. If the pinout in PHYSICAL SETUP
is used, this will be `0x48' (which is the default if not supplied).
device => $string
Optional. The filesystem path to the i2c device file. Defaults to
`/dev/i2c-1'
channel => $int
Optional. See INPUT CHANNELS for parameter values and details.
gain => $int
Optional. See GAIN AMPLIFIER for parameter values and details.
mode => $int
Optional. See OPERATION MODE for parameter values and details.
rate => $int
Optional. See DATA RATE for parameter values and details.
polarity => $int
Optional. See COMPARATOR POLARITY for parameter values and details.
queue => $int
Optional. See COMPARATOR QUEUE for parameter values and details.
addr
Sets/gets the ADC memory address. After object instantiation, this
method should only be used to get (ie. don't send in any parameters).
Parameters:
$hex
Optional: A memory address in the form `0xNN'. See PHYSICAL SETUP for
full details.
device
Sets/gets the file path information for the i2c device. This shouldn't
be used as a setter after object instantiation. It defaults to
`/dev/i2c-1' if not set in the `new()' call (or with this method
thereafter).
Parameters:
$dev
Optional: String, the full path of the i2c device in use. Defaults to
`/dev/i2c-1'.
model
Sets/gets the model of the ADC chip that we're connected to. This
shouldn't be set after object instantiation. Defaults to `ADS1015' if
not set in the `new()' call, or later with this method.
Parameters:
$model
Optional: String, the model name of the ADC unit. Defaults to `ADS1015'.
Valid values are `/ADS1[01]1[3458]/'.
channel
Sets/gets the currently registered ADC input channel within the object.
Both single-ended and differential operation mode are available.
Parameters:
$channel
Optional: See INPUT CHANNELS for the parameter values and details.
gain
Sets/gets the programmable gain amplifier.
Parameters:
$int
Optional: See GAIN AMPLIFIER for the parameter values and details.
mode
Sets/gets the conversion operation mode, either single conversion or
continuous conversion.
Parameters:
$int
Optional: See OPERATION MODE for the parameter values and details.
rate
Sets/gets the data rate.
Parameters:
$int
Optional: See DATA RATE for the parameter values and details.
polarity
Sets/gets the comparitor polarity.
Parameters:
$int
Optional: See COMPARATOR POLARITY for the parameter values and details.
queue
Sets/gets the comparator queue configuration.
Parameters:
$int
Optional: See COMPARATOR QUEUE for the parameter values and details.
OPERATIONAL METHODS
These methods are for core operation, but are left public as they may be
of use for those who want to tinker with the innards.
bits
Separates the 16-bit wide configuration register and returns an array
containing the Most Significant Byte as the first element, and the Least
Significant Byte as the second element.
Parameters: None
Return: Array of two elements (MSB, LSB).
register
Sets/gets the ADC's config register. This has been left public for
convenience for those who understand the hardware very well. It really
shouldn't be used otherwise.
Parameters:
$msb, $lsb
Optional: If one is sent in, both must be sent in. `$msb' is the most
significant byte of the config register, an integer between 0-255.
`$lsb' is the least significant byte of the config register, and must be
in the same format as the `$msb'.
Return: Array with two elements. First element is the MSB, and the
second element is the LSB.
DATA RETRIEVAL METHODS
volts
Retrieves the voltage level of the channel.
Parameters:
$channel
Optional: See INPUT CHANNELS for parameter values and details. Specifies
the ADC input channel to read from. Setting this parameter allows you to
read all four channels without changing the default set in the object.
Return: A floating point number between `0' and the maximum voltage
output by the Pi's GPIO pins.
percent
Retrieves the ADC channel's input value by percentage of maximum input.
Parameters: See `$channel' in volts.
raw
Retrieves the raw value of the ADC channel's input value.
Parameters: See `$channel' in volts.
C FUNCTIONS
The following C functions aren't meant to be called directly. Rather,
use the corresponding Perl object methods instead.
fetch
Fetches the raw data from the channel specified.
Implemented as:
int
fetch (addr, dev, wbuf1, wbuf2, res)
int addr
char * dev
char * wbuf1
char * wbuf2
int resolution
`wbuf1' is the most significant byte (bits 15-8) for the configuration
register, `wbuf2' being the least significant byte (bits 7-0).
voltage_c
Fetches the ADC input and returns it as the actual voltage.
Implemented as:
float
voltage_c (addr, dev, wbuf1, wbuf2, res)
int addr
char * dev
char * wbuf1
char * wbuf2
int resolution
See fetch for details on the `wbuf' arguments.
raw_c
Fetches the ADC input and returns it in its raw form.
Implemented as:
int
raw_c (addr, dev, wbuf1, wbuf2, res)
int addr
char * dev
char * wbuf1
char * wbuf2
int resolution
See fetch for details on the `wbuf' arguments.
percent_c
Fetches the ADC input value as a floating point percentage between
minimum and maximum input values.
Implemented as:
float
percent_c (addr, dev, wbuf1, wbuf2, res)
int addr
char * dev
char * wbuf1
char * wbuf2
int resolution
See fetch for details on the `wbuf' arguments.
TECHNICAL DATA
REGISTERS
Both the conversion and configuration registers are 16-bits wide.
The write buffer for the config register consists of an array with three
elements. Element `0' is the register pointer, which allows you to
select the register to use. Value `0' for the conversion register and
`1' for the configuration register.
Element `1' is a byte long, and represents the most significant bits
(15-8) of each 16-bit register, while element `2' represents the least
significant bits, 7-0.
It is advised that you don't change any of these except for the input
channels unless you know how the hardware works, and you have a good
understanding of the specific configuration register options.
CONFIG REGISTER
CONVERSATION BIT
Bit: 15
This bit should always be set to `1' when writing. This initiates a
conversation with the ADC. When reading, this bit will read `1' if a
conversion is currently occuring, and `0' if the current conversion is
complete.
INPUT CHANNELS
Bit: 14-12
Represents the ADC input channel, as well as either a single-ended
(difference between a single input channel and GRD) or differential mode
(difference between two input channels).
Single mode configuration:
Param Value Input
---------------------
0 100 A0 (default)
1 101 A1
2 110 A2
3 111 A3
Differential mode configuration:
Param Value Diff between
----------------------------
4 000 A0 <-> A1
5 001 A0 <-> A3
6 010 A1 <-> A3
7 011 A2 <-> A3
GAIN AMPLIFIER
Bit: 11-9
Represents the programmable gain amplifier. This software uses `1' or
+/-4.096V to cover the Pi's 3.3V output.
Param Value Gain
--------------------
0 000 +/-6.144V
1 001 +/-4.096V (default)
2 010 +/-2.048V
3 011 +/-2.024V
4 100 +/-0.512V
5 101 +/-0.256V
6 110 +/-0.256V
7 111 +/-0.256V
OPERATION MODE
Bit: 8
Represents the conversion operation mode. We use the single conversion
hardware default.
Param/Value Mode
------------------
0 continuous conversion
1 single conversion (default)
DATA RATE
Bit: 7-5
Represent the data rate. We use 128SPS (128 Samples Per Second) by
default:
Param Value Rate
--------------------
0 000 128SPS (default)
1 001 250SPS
2 010 490SPS
3 011 920SPS
4 100 1600SPS
5 101 2400SPS
6 110 3300SPS
7 111 3300SPS
COMPARATOR POLARITY
Bit: 3
Represents the comparator polarity. We use `0' (active low) by default.
Param/Value Polarity
----------------------
0 Active Low (default)
1 Active High
COMPARATOR QUEUE
Bit: 1-0
Represents the comparator queue. We use `3' (disabled) by default.
Param Value Queue
---------------------
0 00 Assert after one conversion
1 01 Assert after two conversions
2 10 Assert after four conversions
3 11 Disable comparator (default)
READING DATA
Each channel has a conversion register (that contains the actual analog
input). This register is 16 bits wide. With that said, the most
significant bit is used to identify whether the number is positive or
negative, so technically, for the ADC11xx series ADCs, the width is
actually 15 bits, and the ADC10xx units are 11 bits wide (as the
resolution on these models are only 12-bit as opposed to 16-bit).
See the ADC's datasheet for further information.
NOTES
Bit 4 and 2 of the configuration register are currently unused.
SEE ALSO
WiringPi::API, RPi::WiringPi, RPi::DHT11
AUTHOR
Steve Bertrand, <
[email protected]>
COPYRIGHT AND LICENSE
Copyright (C) 2017 by Steve Bertrand
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself, either Perl version 5.22.2 or, at
your option, any later version of Perl 5 you may have available.
