NAME

DS2450 - Quad A/D Converter

SYNOPSIS

Voltage * 4 and Memory.

20 [.]XXXXXXXXXXXX[XX][/[ PIO.[A-D|ALL] | volt.[A-D|ALL] | volt2.[A-D|ALL] | latestvolt.[A-D|ALL] | latestvolt2.[A-D|ALL] ]]

20 [.]XXXXXXXXXXXX[XX][/[ 8bit/volt.[A-D|ALL] | 8bit/volt2.[A-D|ALL] | 8bit/latestvolt.[A-D|ALL] | 8bit/latestvolt2.[A-D|ALL] ]]

20 [.]XXXXXXXXXXXX[XX][/[ memory | pages/page.[0-3|ALL] | power ]

20 [.]XXXXXXXXXXXX[XX][/[ alarm/high.[A-D|ALL] | alarm/low.[A-D|ALL] | set_alarm/high.[A-D|ALL] | set_alarm/low.[A-D|ALL] | set_alarm/unset | set_alarm/volthigh.[A-D|ALL] | set_alarm/volt2high.[A-D|ALL] | set_alarm/voltlow.[A-D|ALL] | set_alarm/volt2low.[A-D|ALL] ]

CO2 sensor

20 [.]XXXXXXXXXXXX[XX][/[ CO2/ppm | CO2/power | CO2/status ]

FAMILY CODE

SPECIAL PROPERTIES

alarm/high.A ... alarm/high.D alarm.high.ALL

read-write, binary
The alarm state of the voltage channel. The alarm state is set one of two ways:

voltage conversion: Whenever the DS2450 measures a voltage on a channel, that voltage is compared to the high and low limits set_alarm/volthigh and/or set_alarm/voltlow and if the alarm is enabled set_alarm/high and/or set_alarm/low the corresponding flag is set in alarm/high and/or alarm/low
manual set: The flag can be set by a direct write to alarm/high or alarm/low

memory

read-write, binary
32 bytes of data. Much has special implications. See the datasheet.

pages/page.0 ... pages/page.3 pages/page.ALL

read-write, binary
Memory is split into 4 pages of 8 bytes each. Mostly for reading and setting device properties. See the datasheet for details.
ALL is an aggregate of the pages. Each page is accessed sequentially.

PIO.A ... PIO.D PIO.ALL

read-write, yes-no
Pins used for digital control. 1 turns the switch on (conducting). 0 turns the switch off (non-conducting).
Control is specifically enabled. Reading volt will turn off this control.
ALL is an aggregate of the voltages. Readings are made separately.

power

read-write, yes-no
Configure whether the DS2450 is externally powered (as opposed to parasitically powered from the data line).
If configured as powered, the A/D coverter will be set to continuous sampling, and the bus will be released during a single conversion allowing other devices to communicate.
Setting this to 1 when no power is applied to the chip's Vcc will result in wrong voltage readouts. Setting this to 0 when power is applied to the chip's Vcc allows a simultaneous conversion trigger on all DS2450 on a bus. The (always safe) default is 0.

set_alarm/high.A ... set_alarm/high.D set_alarm/high.ALL

set_alarm/low.A ... set_alarm/low.D set_alarm/low.ALL

read-write, yes-no
Enabled status of the voltage threshold. 1 is on. 0 is off.

set_alarm/volthigh.A ... set_alarm/volthigh.D set_alarm/volthigh.ALL

set_alarm/volt2high.A ... set_alarm/volt2high.D set_alarm/volt2high.ALL

set_alarm/voltlow.A ... set_alarm/voltlow.D set_alarm/voltlow.ALL

set_alarm/volt2low.A ... set_alarm/volt2low.D set_alarm/volt2low.ALL

read-write, floating point
The upper or lower limit for the voltage measured before triggering an alarm.
Note that the alarm must be enabled alarm/high or alarm.low and an actual reading must be requested volt for the alarm state to actually be set. The alarm state can be sensed at alarm/high and alarm/low

set_alarm/unset

read-write, yes-no
Status of the power-on-reset (POR) flag.
The POR is set when the DS2450 is first powered up, and will match the alarm state until explicitly cleared. (By writing 0 to it).
The purpose of the POR is to alert the user that the chip is not yet fully configured, especially alarm thresholds and enabling.

volt.A ... volt.D volt.ALL

volt2.A ... volt2.D volt2.ALL

8bit/volt.A ... 8bit/volt.D 8bit/volt.ALL

8bit/volt2.A ... 8bit/volt2.D 8bit/volt2.ALL

read-only, floating point
Reading one of these nodes triggers a conversion on the specified voltage input(s) with the selected resolution (16 or 8 bit) and returns the sampled voltage(s) with the selected scaling (0 - 5.10V or 0 - 2.55V). The conversion time is about 1.4ms per input for 16-bit and 0.8ms per input for 8-bit. The output feature ( PIO ) is disabled by reading the corresponding node.
ALL is an aggregate of the voltages. Sampling is controlled by the chip and done in the order A, B, C, D, one after another.

latestvolt.A ... latestvolt.D latestvolt.ALL

latestvolt2.A ... latestvolt2.D latestvolt2.ALL

8bit/latestvolt.A ... 8bit/latestvolt.D 8bit/latestvolt.ALL

8bit/latestvolt2.A ... 8bit/latestvolt2.D 8bit/latestvolt2.ALL

read-only, floating point
Returns previously measured voltage on the specified input(s) with the selected scaling (0 - 5.10V or 0 - 2.55V). Resolution and scaling are set by sampling a voltage, not here; the correct latestvolt nodes have to be read to make the result meaningful.
ALL is an aggregate of the voltages and returns all voltage values from the chip.
Reading these nodes will never trigger a voltage conversion. Intended for use in conjunction with /simultaneous/voltage.

CO2 (Carbon Dioxide) SENSOR PROPERTIES

The CO2 sensor is a device constructed from a SenseAir K30 and a DS2450

CO2/power

read-only, floating point
Supply voltage to the CO2 sensor (should be around 5V)

CO2/ppm

read-only, unsigned
CO2 level in ppm (parts per million). Range 0-5000.

CO2/status

read-only, yes-no
Is the internal voltage correct (around 3.2V)?

STANDARD PROPERTIES

address

r_address

read-only, ascii
The entire 64-bit unique ID. Given as upper case hexadecimal digits (0-9A-F).
address starts with the family code
r address is the address in reverse order, which is often used in other applications and labeling.

crc8

read-only, ascii
The 8-bit error correction portion. Uses cyclic redundancy check. Computed from the preceding 56 bits of the unique ID number. Given as upper case hexadecimal digits (0-9A-F).

family

read-only, ascii
The 8-bit family code. Unique to each type of device. Given as upper case hexadecimal digits (0-9A-F).

id

r_id

read-only, ascii
The 48-bit middle portion of the unique ID number. Does not include the family code or CRC. Given as upper case hexadecimal digits (0-9A-F).
r id is the id in reverse order, which is often used in other applications and labeling.

locator

r_locator

read-only, ascii
Uses an extension of the 1-wire design from iButtonLink company that associated 1-wire physical connections with a unique 1-wire code. If the connection is behind a Link Locator the locator will show a unique 8-byte number (16 character hexadecimal) starting with family code FE.
If no Link Locator is between the device and the master, the locator field will be all FF.
r locator is the locator in reverse order.

present (DEPRECATED)

read-only, yes-no
Is the device currently present on the 1-wire bus?

type

read-only, ascii
Part name assigned by Dallas Semi. E.g. DS2401 Alternative packaging (iButton vs chip) will not be distiguished.

ALARMS

None.

DESCRIPTION

1-Wire

1-wire is a wiring protocol and series of devices designed and manufactured by Dallas Semiconductor, Inc. The bus is a low-power low-speed low-connector scheme where the data line can also provide power.

Each device is uniquely and unalterably numbered during manufacture. There are a wide variety of devices, including memory, sensors (humidity, temperature, voltage, contact, current), switches, timers and data loggers. More complex devices (like thermocouple sensors) can be built with these basic devices. There are also 1-wire devices that have encryption included.

The 1-wire scheme uses a single bus master and multiple slaves on the same wire. The bus master initiates all communication. The slaves can be individually discovered and addressed using their unique ID.

Bus masters come in a variety of configurations including serial, parallel, i2c, network or USB adapters.

OWFS design

OWFS is a suite of programs that designed to make the 1-wire bus and its devices easily accessible. The underlying principle is to create a virtual filesystem, with the unique ID being the directory, and the individual properties of the device are represented as simple files that can be read and written.

Details of the individual slave or master design are hidden behind a consistent interface. The goal is to provide an easy set of tools for a software designer to create monitoring or control applications. There are some performance enhancements in the implementation, including data caching, parallel access to bus masters, and aggregation of device communication. Still the fundamental goal has been ease of use, flexibility and correctness rather than speed.

DS2450

The DS2450 (3) is a (supposedly) high resolution A/D converter with 4 channels. Actual resolutin is reporterd to be 8 bits. The channels can also function as switches. Voltage sensing (with temperature and current, but sometimes restricted voltrage ranges) can also be obtained with the DS2436 , DS2438 and DS276x

ADDRESSING

All 1-wire devices are factory assigned a unique 64-bit address. This address is of the form:

Family Code: 8 bits
Address: 48 bits
CRC: 8 bits

Addressing under OWFS is in hexadecimal, of form:

: 01.123456789ABC

where 01 is an example 8-bit family code, and 12345678ABC is an example 48 bit address.

The dot is optional, and the CRC code can included. If included, it must be correct.

DATASHEET

DS2450: http://pdfserv.maxim-ic.com/en/ds/DS2450.pdf
CO2 sensor: http://www.senseair.se/Datablad/k30%20.pdf
CO2 device: https://www.m.nu/co2meter-version-2-p-259.html?language=en

AVAILABILITY

http://www.owfs.org

AUTHOR

Paul Alfille (paul.alfille@gmail.com)