NAME

DS2437 - Smart Battery Monitor

SYNOPSIS

Temperature Voltages and Memory.

FAMILY CODE

SPECIAL PROPERTIES

date

read-write, ascii
26 character date representation of the counter value. Increments once per second.
Setting date to a null string will put the current system time.
Accepted date formats are: Sat[urday] March 12 12:23:59 2001 Apr[il] 4 9:34:56 2002 3/23/04 23:34:57 current locale setting (your system's format)

current

read-only, integer
Current reading. Actual current depends on Rsens resistor (see datasheet).
The formula for current is I = current /(4096*Rsens)
with units in Amps and Ohms.
Current measurement will be temporarily enabled (see Ienable ) if not currently enabled (pun intended) for this reading.

disconnect/date

read-write, ascii
26 character date representation of the disconnect/udate value. Time when the battery pack waws removed from the charger. Format is the same as the date property.

disconnect/udate

read-write, unsigned integer
Representation of disconnect/date as a number. See udate for details.

endcharge/date

read-write, ascii
26 character date representation of the endcharge/udate value. Format is the same as the date property.

endcharge/udate

read-write, unsigned integer
Representation of endcharge/date as a number. See udate for details.

Ienable

read-write, unsigned integer
Status of current monitoring. When enabled, current sensing is performed 36.41 times/second. Values of Ienable are:

0: no current conversion
1: current conversion enabled
2: current conversion and accumulation
3: current conversion and accumulation with EEPROM backup

pages/page.0 ... pages/page.7 pages/page.ALL

read-write, binary
Memory is split into 8 pages of 8 bytes each. Only the pages 3-7 are really available, and some of that appears to be reserved. See the datasheet for details.
ALL is an aggregate of the pages. Each page is accessed sequentially.

temperature

read-only, floating point
Temperature read by the chip at high resolution (~13 bits). Units are selected from the invoking command line. See owfs(1) or owhttpd(1) for choices. Default is Celsius. Conversion takes ~20 msec.

udate

read-write, unsigned integer
Time represented as a number. udate increments once per second.
Usually set to unix time standard: number of seconds since Jan 1, 1970. The date field will be the unix representation (ascii text) of udate and setting either will change the other.

VAD VDD

read-only, floating point
Voltage read (~10 bits) at the one of the chip's two supply voltages. Range VDD= 2.4V to 10V, VAD=1.5 to 10V.

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.

DS2437

The DS2437 (3) is an obsolete version of the DS2438 (3) battery chip. Current sensing is available, but not implemented. The major advantage compared to the DS2436 is that two voltages can be read, allowing correcting circuit nmeasurements to supply voltage and temperature. A better comparison is the DS276x family of chips.

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

http://pdfserv.maxim-ic.com/en/ds/DS2437.pdf
http://pdfserv.maxim-ic.com/en/an/humsensor.pdf

AVAILABILITY

http://www.owfs.org

AUTHOR

Paul Alfille (paul.alfille@gmail.com)