Sparkfun RV-1805 Technisches Dokument

Qwiic Real Time Clock Module (RV-1805) Hookup Guide

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Introduction

The Qwiic Real Time Clock (RTC) module is a Qwiic-enabled breakout board for the RV-1805 module! The RTC is

ultra-low power (running at about 22 nA in its lowest power setting) so it can use a supercapacitor for backup

power instead of a normal battery. This means infinite charge and discharge cycles without any degradation to the

“battery” (in this case, a supercapacitor). The breakout board is also a part of SparkFun’s Qwiic system, so you

won’t have to do any soldering to figure out what time it is.

In this hookup guide, we’ll take advantage of the Arduino IDE to automatically set the time of the RTC to the

compiler time. Once we have the time set, we’ll set the alarm to a time of our choice and have it generate a signal

on the interrupt pin. We’ll also look at how charged the RTC is so we know when to unplug the RTC from power

(when it’s full of course). Finally, we’ll look at how to store other data into the RTC so we can keep important

variables safe when our system loses power. We’ll also go over how to extend the battery life of your RTC by

adding an external battery.

Required Materials

To get started, you’ll need a microcontroller to control everything in your project.

SparkFun Real Time Clock Module - RV-1805 (Qwiic)

 BOB-14558

Now to get your microcontroller into the Qwiic ecosystem, the key will be one of the following Qwiic shields to
match your preference of microcontroller:
SparkFun RedBoard - Programmed with
Arduino
 DEV-13975
SparkFun ESP32 Thing
 DEV-13907
Raspberry Pi 3
 DEV-13825
Particle Photon (Headers)
 WRL-13774
SparkFun Qwiic Shield for Arduino
 DEV-14352
SparkFun Qwiic HAT for Raspberry Pi
 DEV-14459

You will also need a Qwiic cable to connect the shield to your RTC, choose a length that suits your needs.
Finally, if your application requires that your RTC be without power for over a month, we’d recommend using the
optional battery and battery holder to extend the time that the RTC will remain active without power.
SparkFun Qwiic Shield for Photon
 DEV-14477
Qwiic Cable - 200mm
 PRT-14428
Qwiic Cable - 100mm
 PRT-14427
Qwiic Cable - 500mm
 PRT-14429
Qwiic Cable - 50mm
 PRT-14426
Coin Cell Battery - 12mm (CR1225) Coin Cell Battery Holder - 12mm (PTH)

Suggested Reading

If you aren’t familiar with our new Qwiic system, we recommend reading here for an overview. We would also

recommend taking a look at the hookup guide for the Qwiic Shield if you haven’t already. Brushing up on your

skills in I C is also recommended, as all Qwiic sensors are I C.

Hardware Overview

Let’s look over a few characteristics of the RV-1805 RTC so we know a bit more about how it behaves.

Characteristic Range

Operating Voltage (Startup) 1.6V - 3.6V

Operating Voltage (Timekeeping) 1.5V - 3.6V

Operating Temperature -40°C - 85°C

 PRT-00337  PRT-07948

2 2

How to Solder: Through-Hole Soldering

This tutorial covers everything you need to know about

through-hole soldering.

I2C

An introduction to I2C, one of the main embedded

communications protocols in use today.

Qwiic Shield for Arduino & Photon Hookup

Guide

Get started with our Qwiic ecosystem with the Qwiic

shield for Arduino or Photon.

Time Accuracy ±2.0 ppm

Current Consumption 22 nA (Typ.)

I C Address 0xD2

Pins

The characteristics of the available pins on the RTC are outlined in the table below.

Label

Function

Input/Output Notes

3.3V Power

Supply

Input Should be between 1.95 - 3.6V

GND Ground Input 0V/common voltage.

SDA I C Data

Signal

Bi-directional Bi-directional data line. Voltage should not exceed power supply (e.g.

3.3V).

SCL I C Clock

Signal

Input Master-controlled clock signal. Voltage should not exceed power

supply (e.g. 3.3V).

PSW Power

Switch

Output Power Switch pin, digital output. Capable of switching power on an

external microcontroller.

INT Interrupt Output Interrupt pin, active low, digital output. Also configurable as a square

wave up to 32.768 kHz

RST Reset Output Reset pin, active low, digital output

Optional Features

The Qwiic RTC has onboard I C pull-up resistors, which can be removed by removing the solder from the jumper

highlighted below. Only remove this solder if you are using your own pull-ups on the I C lines.

There is also the option to add a battery to the board if the supercapacitor just isn’t gonna keep your project

powered long enough (keep in mind, the supercap can hypothetically make the board keep time for around 35

days) you can solder on an external battery. Keep in mind that if doing so, you’ll need to cut the trace connecting

power to the capacitor, and add solder to the side of the jumper that connects power to the battery labeled as BAT.

Hardware Assembly

If you haven’t yet assembled your Qwiic Shield, now would be the time to head on over to that tutorial.

With the shield assembled, Sparkfun’s new Qwiic environment means that connecting the sensor could not be

easier. Just plug one end of the Qwiic cable into the RTC breakout, the other into the Qwiic Shield of your choice.

You’ll be ready to upload a sketch and start keeping track of the time. It seems like it’s too easy too use, but that’s

why we made it that way!

External Coin Cell Battery

Now if you’ve decided that you’d like to power the RTC from a battery instead of a supercapacitor, you’ll need to

cut the trace jumper on the back of the board to disconnect power from the supercapacitor. Add solder to the other

side of the jumper to connect power to the battery. Once you’ve done this, add a little bit of solder on the circular

pad for contact, solder the battery holder legs to the board, insert the battery, and you’re good to go!

Library Overview

Note: This example assumes you are using the latest version of the Arduino IDE on your desktop. If this is

your first time using Arduino, please review our tutorial on installing the Arduino IDE. If you have not

previously installed an Arduino library, please check out our installation guide.

Before we get into programming our RTC, let’s download and check out the available functions in our library.

SparkFun has written a library to control the Qwiic RTC. You can obtain these libraries through the Arduino Library

Manager. Search for SparkFun Qwiic RTC RV1805 Arduino Library to install the latest version. If you prefer

downloading the libraries from the GitHub repository and manually installing it, you can grab them here:

DOWNLOAD THE SPARKFUN QWIIC RTC RV1805 LIBRARY (ZIP)

Let’s get started by looking at the functions that set up the RTC.

Setup and Settings

boolean begin( TwoWire &wirePort = Wire ); — The begin function initalizes the RTC, enabling the

trickle charging circuit along with low power mode. Also sets the RTC to a 12-hour time format.

void reset(void); — Performs a full software reset on the RTC.

bool setToCompilerTime(); — Set’s the RTC to the time on the compiler.

bool setTime(uint8_t hund, uint8_t sec, uint8_t min, uint8_t hour, uint8_t date, uint8_t month, uin

— Set’s the time registers of the RTC to a chosen time using individual variables.

bool setTime(uint8_t * time, uint8_t len) — Set’s the time registers of the RTC to a chosen time

using an array of times in the following order

{Hundredths, Seconds, Minutes, Hours, Date, Month, Year, Day} . Please note uint8_t len must be 7,

the length of the time array, for this function to set the time properly.

bool setHundredths(uint8_t value); — Sets the hundredths register to value .

bool setSeconds(uint8_t value); — Sets the seconds register to value .

bool setMinutes(uint8_t value); — Sets the minutes register to value .

bool setHours(uint8_t value); — Sets the hours register to value .

bool setWeekday(uint8_t value); — Sets the weekday register to value .

bool setDate(uint8_t value); — Sets the date register to value .

bool setMonth(uint8_t value); — Sets the month register to value .

bool setYear(uint8_t value); — Sets the year register to value .

void set12Hour(); — Sets the RTC to 12 hour mode.

void set24Hour(); — Sets the RTC to 24 hour mode.

void enableTrickleCharge(uint8_t diode = DIODE_0_3V, uint8_t rOut = ROUT_3K); — Connects an

internal diode and resistor to enable the trickle charging circuit to charge the supercapacitor. The default

values are the fastest for charging the capacitor, although other globally scoped variables (listed below) can

be passed to change the value of the diode and resistor using in the charging circuit.

DIODE_0_3V — 0.3V Diode

DIODE_0_6V — 0.6V Diode

DIODE_DISABLE — Disconnects diode, disables trickle charging circuit

ROUT_3K — 3 kΩ Resistor

ROUT_6K — 6 kΩ Resistor

ROUT_11K — 11 kΩ Resistor

ROUT_DISABLE — Disconnects resistor, disables the trickle charging circuit.

void disableTrickleCharge(); — Disables the trickle charging circuit.

void enableLowPower(); — Enables switching to the low power RC oscillator when the RTC is powered by

the supercapacitor or battery.

Interrupt Functionality

void enableInterrupt(uint8_t source); — Enables a given interrupt based on the value of source ,

which can be any of the following.

INTERRUPT_EIE — External Interrupt

INTERRUPT_AIE — Alarm Interrupt

INTERRUPT_TIE — Timer Interrupt

INTERRUPT_BLIE — Battery Interrupt

void disableInterrupt(uint8_t source); — Disables a given interrupt based on the value of source ,

see above for possible values of source .

void clearInterrupts(); — Clears all interrupt sources.

bool setAlarm(uint8_t sec, uint8_t min, uint8_t hour, uint8_t date, uint8_t month); — Sets the

alarm to a chosen time using individual variables.

bool setAlarm(uint8_t * time, uint8_t len); — Sets the alarm to a chosen time using an array of

times. uint8_t len must be 7, the length of the time array, for this function to set the alarm properly.

enableAlarmInterrupt(); — Attaches the interrupt pin to the alarm function.

void setAlarmMode(uint8_t mode); — mode must be between 0 and 7, alarm goes off with match of

second, minute, hour, etc depending on the value of mode .

0: Disabled

1: Hundredths, seconds, minutes, hours, date and month match (once per year)

2: Hundredths, seconds, minutes, hours and date match (once per month)

3: Hundredths, seconds, minutes, hours and weekday match (once per week)

4: Hundredths, seconds, minutes and hours match (once per day)

5: Hundredths, seconds and minutes match (once per hour)

6: Hundredths and seconds match (once per minute)

7: Depends on the alarm value for hundredths.

0-99 : Hundredths match (once per second)

240-249 : Once per tenth (10 Hz)

255 : Once per hundredth (100 Hz)

void enableBatteryInterrupt(uint8_t voltage, bool edgeTrigger); — Enables the battery interrupt and

sets the voltage at which the interrupt is triggered. The trigger voltages for different values of voltage and

edgeTrigger are found in the table below.

Voltage EdgeTrigger = true EdgeTrigger = false

03.0V 2.5V

12.5V 2.1V

22.2V 1.8V

31.6V 1.4V

void setReferenceVoltage(uint8_t voltage, bool edgeTrigger); — Can be used to set the reference

voltage used for the battery interrupt. Use the values in the above table.

bool checkBattery(uint8_t voltage, bool edgeTrigger); — Checks if the battery level is above the

threshold set by the values voltage and edgeTrigger .

Reading the RTC

bool updateTime(); — Updates the local time array with the RTC time registers.

stringDateUSA(); — Returns the date in MM-DD-YYYY format.

stringDate(); — Return date in DD-MM-YYYY format.

stringTime(); — Return time in HH:MM:SS with AM/PM if the RTC is in 12 hour mode.

uint8_t getHundredths(); — Returns the value of the hundredths register.

uint8_t getSeconds(); — Returns the value of the seconds register.

uint8_t getMinutes(); — Returns the value of the minutes register.

uint8_t getHours(); — Returns the value of the hours register.

uint8_t getWeekday(); — Returns the value of the weekday register.

uint8_t getDate(); — Returns the value of the date register.

uint8_t getMonth(); — Returns the value of the month register.

uint8_t getYear(); — Returns the value of the year register.

bool is12Hour(); — Returns true if 12hour bit is set.

bool isPM(); — Returns true if is12Hour() == true and PM bit is set.

uint8_t status(); — Returns the status byte.

uint8_t BCDtoDEC(uint8_t val); — Converts from BCD to decimal format.

uint8_t DECtoBCD(uint8_t val); — Converts from decimal to BCD format.

uint8_t readRegister(uint8_t addr); — Reads the register at addr .

bool writeRegister(uint8_t addr, uint8_t val); — Writes val to location addr .

bool readMultipleRegisters(uint8_t addr, uint8_t * dest, uint8_t len); — Reads len number of

registers, incrementing up from the addr location, into the array dest .

bool writeMultipleRegisters(uint8_t addr, uint8_t * values, uint8_t len); — Writes len number

of registers, incrementing up from the addr location, from the array values .

Example Code

Example 1 - Set Time

Once you’ve installed the SparkFun Qwiic RTC RV-1805 Arduino library go to File > Examples > SparkFun Qwiic

RTC RV-1805 Arduino Library > Example1-Set_Time to open the example sketch. We will use this first sketch to

set up our RTC’s internal clock. Take note of the following lines of code, which use the compiler time to set the

RTC’s clock.

if (rtc.setToCompilerTime() == false) {

Serial.println("Something went wrong setting the time");

}

Note that this doesn’t reset every time we upload code into our Arduino, so make sure you restart the IDE before

uploading to get the most current time to upload into your RTC.

Example 2 - Print Time

Now that we’ve set the time on the RTC, let’s read it out. Open the next example by heading to File > Examples >

SparkFun Qwiic RTC RV-1805 Arduino Library > Example2-Print_Time to open the example sketch. After

initializing the RTC object, we attempt to update the time variables in our microcontroller with the values from the

RTC using some of the code below. If this is successful, we print them out.

if (rtc.updateTime() == false) //Updates the time variables from RTC

{

Serial.print("RTC failed to update");

}

Also, in its need to feel special, the United States formats its dates differently than the rest of the world (We do

MM/DD/YYYY format while everybody else does DD/MM/YYYY format). So if you don’t live in the U.S. or you just

like how the rest of the world formats their dates, you’ll need to uncomment the following line of code (line 50) in

your sketch.

//String currentDate = rtc.stringDate());

Once you upload this code to your microcontroller, go ahead and open the serial monitor with a baud rate of 9600.

You should see the current date and time go streaming past, looking something like the image below.

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