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I2C in Pi PICO || Simple Device || LCD16x2 Using I2C
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Apr 11, 2021
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View Video Transcript
0:12
hello
0:13
everyone welcome to another video in the
0:16
raspberry pi pico series
0:19
in this video we will cover how to use i
0:22
squared
0:22
c with the pico of course
0:25
i will first demonstrate the simple i
0:28
squared c
0:28
device and later we will interface a 16
0:31
by 2 lcd display
0:34
the device i am using for this video is
0:36
pcf 8574
0:39
it's an i squared c device obviously
0:43
you can see the input pins here clock
0:46
data
0:46
vcc and the ground
0:50
it have 16 pins which connects to the
0:52
lcd display
0:54
but that part will come later out of
0:57
those 16
0:58
pins these seven pins are the actual
1:00
pins where we can control the output
1:04
we have a group of p4 to p7 and another
1:07
group of p0 to p2
1:10
p3 is the pin after p7 and i am not
1:13
using it in this section of the tutorial
1:17
let's say if we send a 1 to this device
1:19
the pin p0 will be set high
1:23
similarly if we send a 2 the pin p1 will
1:26
be high
1:28
sending 4 will set the p2 high
1:33
and similarly sending a 16 32
1:37
64 and 128 will turn on the higher four
1:41
pins i will demonstrate this in a minute
1:45
let's start the thunni id
1:52
i will connect my pico and select this
1:54
stop here
1:56
you can see the pico is connected now
2:03
let's start by importing the i squared c
2:06
and the pin module
2:16
import time for delay purposes
2:19
before we go any further let's see the
2:21
pico pin out
2:24
i am going to use the i2c one for this
2:26
tutorial
2:28
as you can see the pins 27 is the clock
2:31
pin
2:32
and 26 is the data pin
2:35
also i am going to power the device with
2:37
this 3.3 volts and ground
2:41
now first we will create an i2c object
2:45
the first parameter is the i2c bus and
2:48
this will be one
2:50
then the clock pin data pin
2:54
and at last the frequency let's keep it
2:57
100 kilohertz
3:00
now we will scan the device for its
3:02
address
3:04
we need to call the i2c scan for this
3:06
purpose
3:11
save the file directly to the pico
3:22
seems like i typed in the wrong keyword
3:26
okay so we got 39 here this is the
3:29
address of our slave device
3:32
let's understand why
3:38
this is the data sheet for the pcf-8574
3:44
here you can see bunch of addresses are
3:46
given
3:47
actually the address of the device can
3:49
be modified up to some extent
3:53
this depends on these three pins a0
3:56
a1 and a2 the very
4:00
next pins are the ground pins
4:03
if you connect any of these pins to the
4:05
ground the address of the device will
4:07
change
4:08
and that explains all these high and low
4:11
addresses here
4:13
right now all three pins are high so the
4:16
address will be 0 cross 4
4:18
e or 78 but that's not the address we
4:22
were shown in the console
4:25
actually this here is the 8-bit address
4:29
which consists of the 7-bit address plus
4:32
1 read or write bit
4:34
to indicate the type of operation
4:37
pico just like arduino uses the 7 bits
4:40
for the address
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excluding the read or write bit so to
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get the address
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we need to shift this address by one
4:48
place to the right
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so we have 1 1 1 0 for the lower 4 bits
4:54
and 0 1 0 for the upper 3 bits
4:57
this makes up 0 cross 2 7 which is 39 in
5:01
decimal
5:05
let's write our program now
5:13
here i am shifting the one by four
5:15
places and storing it in the value
5:19
as i explained in the beginning that we
5:21
can control these seven output pins from
5:23
the device
5:25
i have four leds connected to these four
5:28
pins
5:29
so in order to set the pin p4 i need to
5:32
write a one in that position
5:34
and to do that i am shifting the one by
5:37
4 places
5:39
now use right to function to write the
5:41
data to the device
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first parameter is the device address
5:46
and then the buffer to the data
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you want to send i am using bytes to
5:51
convert the value to the byte
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let's run this
5:58
you can see the first led is on
6:03
and if we send one to the fifth position
6:06
the second ad is on
6:11
now the third
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and the last one is on now
6:24
if we want to turn all of them on well
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we can send 15
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which corresponds to 1 1 1 1.
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you see all the leds are on now
6:37
let's create a function to do this task
6:43
i am using the for loop in the range
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from 4 to 8
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here 8 is not included in the range
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now shift the 1 according to the value
6:53
of x
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and send this value to the device
6:58
we will repeat this every 500
7:00
milliseconds
7:02
now define the main function where the
7:04
above function will be in the while loop
7:08
and this line to call the main function
7:13
let's run it we have an error in pcf
7:17
led it's because of this spelling
7:21
mistake
7:22
okay let's try it again
7:27
you can see the leds are blinking every
7:30
500 milliseconds
7:33
so everything is good this is how you
7:36
can use the i squared c
7:38
at the basic level
7:43
that's it for the first part
7:48
now in the second part of this video we
7:50
will interface the lcd 16x2 using the
7:56
i2c
7:58
i have created a python file for this
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and i will explain all the steps
8:07
first of all we will import the i2c and
8:09
create the object
8:11
as we did previously
8:15
i am using the datasheet which is
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available here
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in order to interface this lcd or any
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other device
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we have to send some commands and some
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data
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these are the functions defined to do so
8:34
here you can see how the pcf 8574
8:37
is connected to the lcd this rs pin
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decides
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whether the value sent is a command or
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data
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basically to send the command this pin
8:49
must be low
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and to send the data it must be high
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is is connected to the pin p0 of the pcf
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then another important thing you need to
9:00
know is the pins d4 to d7 of the lcd
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are connected to the pins p4 to p7 of
9:06
the pcf
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we are going to use the display in the
9:10
4-bit mode
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so we only need 4 data pins
9:15
the lower data pins are not connected to
9:17
anything
9:19
since we are only using 4 data pins we
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will separate the 8-bit command in the
9:24
two halves
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the upper half and the lower half
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here i am adding the upper half with the
9:31
zero cross
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zero c the reason is simple
9:38
whenever we send the command or data to
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the display
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we must turn the enable bit high and
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then low
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this enable strobe will make the data
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transferred to the lcd
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now here i am keeping the enable pin
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high that means the p2 is high
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this will make the zero cross zero four
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also like i said in the beginning the
10:02
backlight of the display is connected to
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the p3
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so we need to keep it high 2 and since
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it's a command
10:09
the rs pin must be low that makes the p0
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as low
10:14
adding them together we have to keep the
10:16
p2 and p
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3 high and p 0 as low
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this makes up 0 cross 0 c
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after sending it we will send 0 cross 0
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8
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basically the same as last case but this
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time the enable is low
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remember the enable strobe first keep it
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high
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then low this will transfer the upper
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half of the command
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in the same way we will transfer the
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lower half
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to first send with enable high
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and then with enable low and
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finally we will write the values to the
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i2c device in this sequence
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this print function here is just kept
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for debugging purpose
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in case you want to check if the
11:09
commands are correct or not
11:12
sending data is similar to command
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we separate the upper half and the lower
11:18
half
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then we add with zero cross zero d this
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time
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this is because while sending the data
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we must keep the rs pin high
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this will tell the display that we are
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sending data this time
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other than that we have to do the same
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like sending command
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send with enable hi and then send with
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enable low
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then here we have the lcd initialization
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sequence
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this sequences as per the instructions
12:01
given in the datasheet of the display
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this is for 8-bit interface but since we
12:18
are only using
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four pins we have to use this one
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as mentioned here we have to wait for
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around 15 milliseconds
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or 40 milliseconds then send this
12:30
command
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as you can see here the command is
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written for db4 to db7
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these are the higher data pins in our
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display
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so basically this command will transform
12:44
to zero cross three
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zero
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then wait for more than four
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milliseconds and send the same command
13:00
again wait for 100 microseconds and send
13:04
the same command
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as you can see i am following the
13:08
instructions here
13:10
and then there are other instructions as
13:12
per the data sheet
13:14
you can configure it according to your
13:16
requirement
13:18
like if you want one line or two lines
13:20
or cursor should be a line or block
13:23
or should it be blinking or shifting the
13:26
display
13:27
etc just configure according to the
13:31
requirement you have
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the commands are explained pretty well
13:35
in the data sheet
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this is the function to send the string
13:40
here we use the for loop to keep sending
13:42
individual data to the display
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ord function is used to change any
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character to the respective decimal
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value
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then we have the go to function this is
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to set the cursor at different places on
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the display
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here x is the row and y is column
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here we simply add the column number to
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the zero cross eight zero
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which is the zeroth row or zero cross c
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zero
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which is the first row and at last this
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is the command to clear the display
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now let's see the main file
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we first have to import the library
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let's save the library in the pico first
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okay now we will initialize the display
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go to zeroth row and first column
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print something go to first row first
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column
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and print another thing let's save it to
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our board
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and run it now
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you can see the data is displaying at
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the respective locations
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now let's assume you want to send the
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number or a float value to this display
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i am going to send 123.
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and 123.45
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clear the display and go to 0 1
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and send the number by converting it to
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the string
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do the same for float
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as you can see the data is displaying as
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expected
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this is it for this video i know the
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library
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is not written according to the python
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standard but i am more
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of a c person i don't have a very good
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command over python yet
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but this works well for now maybe in the
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future
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as i get more experienced with python i
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will update these libraries
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you can download the code from the
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github the link is in the description
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keep watching and have a nice day ahead
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do
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you
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