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DS3231 RTC Module and STM32 || cubeide || I2C-LCD
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Jan 4, 2020
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View Video Transcript
0:07
hello welcome to controllers tech few
0:12
months ago I made a video about using
0:15
internal RTC in stm32 although
0:19
everything was pretty ok with that
0:21
there was the problem of storing time
0:24
whenever the controller lost power the
0:27
RTC used to reset itself today in this
0:31
video we are going to interface ds3231
0:34
RTC module with SDM 32 as mentioned in
0:39
the datasheet you can use 2.3 to 5 point
0:42
5 volts to power the module we can also
0:51
use i2c in fast mode or the standard
0:54
mode to read or write data and then we
1:03
have these registers that we are going
1:05
to write to and read the time from so
1:09
let's start with the cube IDE
1:27
create a new project I am using stm32
1:34
f103 c8 controller give a name to the
1:42
project and click Next
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just want to show you the firmware
1:54
version at the time of making this video
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click finish and the cube MX will open
2:04
so first things first I am enabling the
2:08
clock from the external crystal next
2:12
enable the i2c and clock and data pins
2:15
will be selected this is how the
2:24
connection will be ds3231 is connected
2:29
to the controller via i2c one and PCF
2:33
eight five seven four is also connected
2:35
to the same i2c bus and then to the LCD
2:39
I want to run the clock at maximum so
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just type in 72 and hit enter go to sis
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debug and select serial wire click Save
2:56
and the project will be generated
3:06
[Music]
3:07
here is the main C file first of all we
3:13
need to include the LCD library because
3:15
I want to display the time and date on
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the LCD copy the C file in the source
3:21
and header file in the include folders
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you can get these files after you
3:27
download the project from the link in
3:29
the description this address is defined
3:32
for PCF eight five seven four if you are
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using any other I - C extender you have
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to change this
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let's include the header file in our
3:55
project
4:05
if you look at the datasheet of the
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ds3231 you can find the i2c address this
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is the address defined for the right
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cycle in stm32 the address should be 8
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bit long which includes 7 bits of the
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address and 1 bit for the right this
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makes up the address of the ds3231 as 0
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cross d0 let's define that address these
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are the functions to convert from BCD
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format to decimal format and vice versa
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the data written to the ds3231 must be
4:51
in the binary coded decimal format and
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that's why we need these functions I am
5:01
defining a structure to save the time
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and date that we are going to read from
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the module
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[Music]
5:17
now let's write a function to set the
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time the parameters are seconds minutes
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our day of week day of month month and
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year I am defining an array to store
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seven bytes of data
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the data written to the module must be
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in this order first time than day of
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week and at last date
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basically we have to write these seven
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registers first we need to convert these
6:08
values to the BCD format using decimal
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to BCD converter the array that I
6:14
created is going to store these BCD
6:16
values for the respective register now
6:22
we are going to write these values to
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the registers we can do that by taking
6:30
advantage of the fact that the address
6:32
of the registers in the module will
6:33
automatically increment with every right
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operation so we just have to write 7
6:39
bytes to this first register and the
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first seven registers will be
6:44
automatically written I am using memory
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write function of how to write the data
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to the specific location in the memory
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device address address of the register
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size of addresses one byte the data that
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we want to write size of data is 7 bytes
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and time out next we need a function to
7:08
read the time from the RTC again
7:12
creating an array to store the BCD
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values that we are going to receive from
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the RTC I am using Hal i2c memory to
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read the data from the memory device
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address address of the memory
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sighs of addresses one bite where we
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want to store this data how many bytes
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to read and time out address of the
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registers Auto increments and we get the
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reading from the first seven registers
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next we need to convert these values to
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the decimal format and then store in the
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time structure I am creating this buffer
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to store the equivalent characters so
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that we can display the result on the
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LCD in the main function initialize the
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LCD then inside the while loop first we
8:19
have to read the time and then convert
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the numbers to the characters using s
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printf function
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[Music]
8:52
put the cursor at 0-0 and display the
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time next convert the date in the
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character format
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put the cursor in the next line and
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display the date
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I am giving 500 milliseconds delay
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between each refresh we have to set the
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time first I am setting it 20 seconds
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later than the actual time let's build
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this code there seems to be some problem
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with s print F
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we have to include the stdio dot h
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I have to change the time again let's
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flash the code select stm32 application
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run it for a little amount of time now
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we need to again flash the code without
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the time setting line so if we reset the
10:53
controller in future the time will not
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set to the same value again now it's
11:07
time to see the actual working the time
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and date is working as it should even if
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I try to reset the controller the time
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continues to work properly
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so I have disconnected them from the
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supply the time is stored in the RTC now
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and we can access it anytime we want as
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you can see it is around nine seconds
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more than the last one
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you need to have a battery if you want
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to store the time so we saw how can we
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set and read the time from the ds3231
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next we are going to read the
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temperature from this module yes it have
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a temperature sensor also as mentioned
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in the datasheet address is 11 H and 12
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H stores the temperature 11 H stores the
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MSB of the temperature data and 12 H
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stores the LSB
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yet temp function is being used to read
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the temperature basically I am going to
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use how memory to read two bytes of data
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from 11h address
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then we need to combine the MSB and LSB
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LSB must be shifted six places to the
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right the result must be divided by four
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because the resolution is 0.25 degrees
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Celsius per bit there is one important
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piece of information before we read the
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temperature the bsy bit in the status
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register this bit goes to 1 when the
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conversion signal is given
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[Music]
13:47
other than this we have convert
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temperature bit in the control register
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setting this bit to one will force the
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conversion if we don't force the
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conversion the temperature conversion
14:00
would take place every 64 seconds by
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default
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[Music]
14:23
[Music]
14:27
this is the function to force the
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conversion here first I am reading the
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status register
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if the BSY bit is not set read the
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control register
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[Music]
15:17
and right the modified value with the
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conversion bit as one
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[Music]
15:38
I am going to force the conversion read
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the temperature and store the value in
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temp variable we need to again use s
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printf to convert this value to the
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characters to convert the float type
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numbers we need to change the setup a
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bit
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go to project setting C++ build settings
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tool setting
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and enable the you printf float feature
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[Music]
16:37
now send the buffer to the LCD let's run
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the code now so here we have the time
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date and temperature from the ds3231 RTC
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module if I hold the device you can see
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the rise in temperature
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again if I disconnect the things would
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still be working fine this is it guys
17:42
ds3231 still have few more features left
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to be covered for example it have two
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alarms oscillator output square wave
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output etc I will cover those in the
17:56
next video real time was the important
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part and so we have covered that today I
18:02
hope you understood the video you can
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download the code from the link in the
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description leave comments if you have
18:12
any doubt keep watching
18:15
[Music]
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