Maxim DS3231 RTC topic

Introduction

The I2C Maxim DS3231 real time clock (RTC) is absolutely required for time-keeping on all AVR boards. This library also makes use of of the DS3231 for its on-board temperature sensor. This temperature is not equivalent to an environmental temperature measurement and should only be used to as a diagnostic. Internally, the DS3231 uses the temperature it measures to compensate for temperature variation in the crystal speed. This improves the timekeeping accuracy and reduces time drift.

The DS3231 requires a 3.3V power supply and most breakouts or boards that integrate the DS3231 (including the Mayfly) use a coin battery to supply the clock. Using separate power supply for the clock prevents the time from resetting if the main board loses power.

Sensor Datasheet

Datasheet

Sensor Constructor

Example Code

The Maxim DS3231 RTC is used in nearly all of the examples, including the menu a la carte example.

Classes

class MaximDS3231

The Sensor sub-class for the Maxim DS3231 when used as a low-accuracy temperature sensor.

class MaximDS3231_Temp

The Variable sub-class used for the temperature output from a DS3231.

Sensor Variable Counts

The number of variables that can be returned by the DS3231

#define DS3231_NUM_VARIABLES = 1

Sensor::_numReturnedValues; the DS3231 can report 1 value.

#define DS3231_INC_CALC_VARIABLES = 0

Sensor::_incCalcValues; we don't calculate any additional values.

Sensor Timing

The sensor timing for a Maxim DS18 RTC

#define DS3231_WARM_UP_TIME_MS = 0

Sensor::_warmUpTime_ms; the DS3231 should never be powered off so there is no warm-up time.

#define DS3231_STABILIZATION_TIME_MS = 0

Sensor::_stabilizationTime_ms; the DS3231 should never be powered off so there is no stabilization time.

#define DS3231_MEASUREMENT_TIME_MS = 200

Sensor::_measurementTime_ms; the DS3231 takes 200ms to complete a measurement - A single temperature conversion takes 200ms.

Temperature

The temperature variable from a Maxim DS18 RTC

• Range is -55°C to 125°C
• Accuracy: ± 3°C

#define DS3231_TEMP_RESOLUTION = 2

Decimals places in string representation; temperature should have 2 - resolution is -0.25°C (10 bit).

#define DS3231_TEMP_VAR_NUM = 0

Sensor variable number; temperature is stored in sensorValues[0].

#define DS3231_TEMP_VAR_NAME = "temperatureDatalogger"

Variable name in ODM2 controlled vocabulary; "temperatureDatalogger".

#define DS3231_TEMP_UNIT_NAME = "degreeCelsius"

Variable unit name in ODM2 controlled vocabulary; "degreeCelsius" (°C)

#define DS3231_TEMP_DEFAULT_CODE = "BoardTemp"

Default variable short code; "BoardTemp".

Define documentation