/ 
RPi-ADC-ADS-0.05
River stage one • 1 direct dependent • 2 total dependents
/ RPi::ADC::ADS

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,
);

my $volts   = $apc->volts;
my $percent = $apc->percent;
my $int     = $apc->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 = $apc->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. One of 0 through A3 which specifies which channel to read. If not sent in, we default to 0 throughout the object's lifecycle.

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.

channel

Sets/gets the currently registered ADC input channel within the object.

Parameters:

$channel

Optional: String, 0 through 3, representing the ADC's multiplexer input channel to read from. Setting through this method overrides the value that was set in new() (0 by default if never specified), until it is changed again. If you are using more than one channel, it's more useful to set the channel in your read calls (volts(), raw() and percent()).

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]/.

register

Sets/gets the ADC's registers. This has been left public for convenience for those who understand the hardware very well. It really shouldn't be used otherwise.

Parameters:

$binary

Optional: A binary string (literal 1s and 0s), 32 bits long that represents the data we'll write to the ADC device.

DATA RETRIEVAL METHODS

volts

Retrieves the voltage level of the channel.

Parameters:

$channel

Optional: String, 0 through 3, representing 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 (ads_address, dev_name, wbuf1, wbuf2, resolution)
    int	ads_address
    const char * dev_name
    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 (ads_address, dev_name, wbuf1, wbuf2, resolution)
    int	ads_address
    const char * dev_name
    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 (ads_address, dev_name, wbuf1, wbuf2, resolution)
    int	ads_address
    const char * dev_name
    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 (ads_address, dev_name, wbuf1, wbuf2, resolution)
    int	ads_address
    const char * dev_name
    char * wbuf1
    char * wbuf2
    int resolution

See "fetch" for details on the wbuf arguments.

TECHNICAL DATA

REGISTERS

The write buffer consists of an array with three elements. Element 0 selects the register to use. 0 for the conversion register and 1 for the configuration register.

Element 1 is a byte long, and represents bits 15-8 of a register, while element 2 represents bits 7-0.

CONFIG REGISTER

Bit 15 should always be set to 1 when writing. This initiates a conversation ADC. When reading, this bit will read 1 if a conversion is currently occuring, and 0 if the current conversion is complete.

Bits 14-12 represent the ADC input channel, as well as either a single-ended (difference between HIGH and GRD) or differential mode (difference between two input channels). Only single-ended is currently supported.

Below is the binary representation for the input channels (bits 14-12):

Input   Binary

A0      100
A1      101
A2      110
A3      111

Bits 11-9 are for the programmable gain amplifier. This software uses 001 or +/-4.096V to cover the Pi's 3.3V output.

000: FS = +/-6.144V              100: FS = +/-0.512V
001: FS = +/-4.096V              101: FS = +/-0.256V
010: FS = +/-2.048V (hw default) 110: FS = +/-0.256V
011: FS = +/-2.024V              111: FS = +/-0.256V

Bit 8 is for the conversion operation mode. We use single conversion hardware default.

0: continuous conversion
1: single conversion (hw default)

Bits 9-5 represent the data rate. We use 128SPS:

000 : 128SPS 100 : 1600SPS (hw default)
001 : 250SPS 101 : 2400SPS
010 : 490SPS 110 : 3300SPS
011 : 920SPS 111 : 3300SPS

Bit 4 is unused.

Bit 3 is the comparator polarity. We use Active Low by default:

0 - Active Low (hw default)
1 - Active High

Bit 2 is unused.

Bits 1-0 represent the comparator queue. This software has disabled it:

00 : Assert after one conversion
01 : Assert after two conversions
10 : Assert after four conversions
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 ADC1xxx 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.

SEE ALSO

WiringPi::API, RPi::WiringPi, RPi::DHT11

AUTHOR

Steve Bertrand, <steveb@cpan.org>

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.