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DS18B20 MULTIPLE SENSORS || UART || STM32
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Dec 11, 2021
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View Video Transcript
0:01
[Music]
0:09
hello and welcome to controllers tech
0:12
few months ago i made a video about
0:15
interfacing ds18b20 temperature sensor
0:17
with stm32
0:20
some of you guys still couldn't make it
0:22
work due to some problems
0:25
this video will take a completely
0:26
different approach towards the same
0:28
sensor and also we will see how to use
0:31
multiple ds-18 v20 sensors using only
0:34
single wire
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we will use the uart to do the
0:38
communication instead of the timer that
0:40
we used last time
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well i couldn't figure out the process
0:45
and therefore i am using a pre-existing
0:47
library for it
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it's right here you can check it out if
0:52
you want to read the details
0:54
this library uses standard peripheral
0:57
driver and i have modified it to use the
1:00
hull
1:01
i hope the author is okay with it
1:04
so today we will see how to use uart
1:06
using this library and interface
1:08
multiple ds18b20 sensors with the sdm 32
1:14
let's start with cube id and create a
1:17
new project
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i am using sdm 32 f103 controller
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give some name to the project and click
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finish
1:35
first of all we will set up the clock
1:38
i am using external high speed crystal
1:41
to provide the clock
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the blue pill have 8 megahertz crystal
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on board and i want to run the system at
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maximum 72 megahertz clock
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now go to the uart and enable the half
1:58
duplex mode
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we will keep everything same here just
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go to the nvic and enable the global
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interrupt
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you can see the half duplex mode uses
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single pin for communication
2:16
this is it for the setup click save to
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generate the project
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before we go any further let's see the
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connections
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you can see here the 2-d s-18 b-20 are
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connected in a way that they're all 3
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wires are attached to each other there
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is a 5 kilo ohms resistor connected
2:38
between the signal wire and the v-c-c
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i am going to provide the common 3.3
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volts to both of them along with a
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common ground
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and the signal pin is connected to the
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p-a-9 the u-r-t-x pin
2:54
this is it for the connection let's see
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the code now
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first of all we will copy the one-wire
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library files into our project
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now pay attention to the changes we need
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to make here
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open the one wire dot c file
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change the uart instance that you are
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using
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i set up the uart one
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now define the maximum number of devices
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you have connected
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i am using 2 devices
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we need to define this in the 1 wire
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header file also
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make sure you make the changes at both
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places
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we also need to configure the interrupt
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file that we will do in a while
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all right now come to the main file and
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include the one wire header file here
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there is a float variable defined in the
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1 wire source file
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this variable will store the temperature
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values and this is why we need to define
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the same in our main file also
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but define it as the external variable
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as it's already defined somewhere else
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now in the main function we will call
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the get wrong id function
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this function will scan for all the
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connected devices and sort them
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according to their ids
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now inside the while loop we will call
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the get temperature function to read the
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temperature from the connected sensors
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these temperature values will be stored
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in the variable we defined in the
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beginning
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you should give a delay of at least 1
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second before reading it again
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now the final thing we need to do is
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modify the interrupt callback function
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so go to the interrupt.c file
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here we will first include the one wire
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header file
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in the 1 wire header file there is a
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function defined o w read handler
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we will call this function in the uart
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interrupt handler
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make sure you keep it in the user code 0
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as it needs to be called before the
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other interrupt handler
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this is it
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now let's build and debug the code
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i have added the temperature array in
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the live expression
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you can see here we are getting two
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different readings
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so both the sensors are working fine
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now i am going to hold one of the
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sensors
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notice the change in the reading you can
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see the temperature of the first sensor
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is rising but the second one is
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unaffected
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so here we have the 2 temperature
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sensors connected on the same pin and
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working as expected
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you can connect up to 64 sensors in this
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mode
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there is one more thing i want to
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mention
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the function get rom id is responsible
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for scanning the connected devices
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here this structure stores the
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information about the device
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let me show this in working
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we hit the break point let's check the
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dev info
6:59
here you can see the information about
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this particular device
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the 28 represents the type of device
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this is defined in the header file
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after this we have the rom id for this
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device
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if we run the code again this time we
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have another device with different rom
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id
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this function sorts out the devices
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based on their rom ids
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the lower the id the lower the rank of
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the device
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the temperature array shows the
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temperature according to the rank
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allotted by the rom id function
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so basically if you want to fix the
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sensors to show the temperature of some
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particular things you either need to
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know their rom ids or you can mark them
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by first measuring the known
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temperatures
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this is it for the video
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i hope you understood the process
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as i mentioned before try to use the use
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art and not the uart for this tutorial
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there are some registers involved in the
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source code so i don't know if the uart
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will work for sure
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but i have tested it with different
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controllers and it works pretty well
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with the use art
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this is it for today
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you can download the code from the link
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in the description
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leave comments in case of any doubt
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keep watching and have a nice day ahead
8:37
[Music]
9:02
you
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