I2C Bus danger of display-damage?

Other Hardware Displays
1

hi all,

Situation : arduino nano , LCD-Display 1602A with I2C

I'm just wiring in a railway-project , its a lot of connections there..

preposing :
-VCC and GND are connected correctly with 5V-Power-Supply

  • ICL-connections are to Pins A4 and A5 of Ardiono Nano like recommended

1st question : If the SCL- and SDA - Pins would be exchanged erraneously,
is it possible that display and/or arduino will be damaged ?

2nd question : can the signals and levels in ICL distinguished
by viewing at an oscilloscope so that one can be shure of correct connection ?

2

1. No.
2. Correct connection can only be ensured by runnibg the following test progrm which will show the message Forum on the LCD.

#include<LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);  //I2C address, 16-chac, 2-line; 

void setup() 
{
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0, 1);  //DPos (0-15), LPos (0-1) = Digit Position, Line Position
  lcd.print("Forum"); 
}

void loop() 
{
 
}

If you don't see the message Forum on the LCD, try again by changing the address at: 0x2F.

3

This is the first time that I read about "ICL" and "I2C" together.

The I2C bus is not that kind of bus. They are weak digital signals, and they are not supposed to go somewhere. They should also not be next to each other in a cable. The I2C bus was not designed to go through a cable. The SDA and SCL signals are only valid with a GND. The GND wire that belongs to SDA and SCL should be treated with the same care.

4

Thanks, all,

typing error in line 6 : meant I2C instead of ICL , sorry

but thats not what I am intended. May be my English is not so good, as its not
my mother tongue, sorry

What I want is to check the wired between Arduino and Disply
BEFORE connecting the display !
To check voltages is simply but to check the I2C - wires i'm unsure..

5

SCL and SDA are clearly marked on the I2C Controller Board. SCL (Serial Clock) will be connected with A5-pin and SDA (Serial Data Line) will be connected with A4-line of UNO.
I2CController

6

ok,
i see, at now nobody understands my question..

7

No.

Yes.

But quite honestly it is much easier to just use different coloured wires e.g.

VCC red    5V
GND black  GND
SCL green  A5
SDA yellow A4

If you write the colours in your sketch, it will help you to connect the correct wire to the correct pin.
Much quicker, easier and cheaper than buying an oscilloscope.

David.

8

It is very unlikely the display would be damaged from an incorrect I2C connection. Reversing SCL and SDA will likely cause the display to completely ignore any communications from the Arduino, because the first thing the Arduino sends is the address for the I2C device, and the I2C device will never respond unless it receives its correct address.

In order to use an oscilloscope to check the connection, the Arduino and LCD would have to be connected and operating, and at that point it is faster to run a test sketch than to try and make measurements. An oscilloscope would likely only show that there is activity on the I2C bus, but not whether the connection was correct, except that generally if the LCD does not respond to the Arduino when the I2C communications is initiated, the Arduino tends to sit and wait for a response and not do anything.

9

hi,
oh now answers fit better..

ad 1) i dont suppose any damage too because
meanwhile i guess Arduino sends PWM-like signals
at A4 / A5

ad 2) I have an tube - driven oscilloscope
but as i have no information about these signals i can only assure that there
will no dangerous energy at the pins..

thanks for your interest .. now i have to leave and do my jobs..
this evenening continuing on my project..

10

This is typical I2C signal signatures (not PWM-like):
i2cSignal

11

[quote="lupus51, post:9, topic:950643"]
ad 1) i dont suppose any damage too because
meanwhile i guess Arduino sends PWM-like signals
at A4 / A5

No, you can use the analog pins are regular digital pins and that is what the Wire (i2c) library does with A4/A5 since those pins are the built-in hardware to drive the i2c bus.

No, there are not dangerous levels on these pins. They are idle at 5V and get pulled down to 0V with minimal current.

12

No possibility at all from simply swapping the two signals.

Total waste of time looking at them with an oscilloscope.

However, if your concern is actually related to connecting it up and it failing to work, the answer is much simpler. :grin:

If you are using the obsolete LiquidCrystal_I2C.h library referenced by GolamMostafa, then it most likely will not work with current 1602 LCD modules which are different from those manufactured back in the days when LiquidCrystal_I2C.h was last updated. :astonished:

You need to go to the IDE Library Manager and install Bill Perry's "HD44780" library and work through the examples provided with that library, notably the "I2CexpDiag" test sketch under libraries/hd44780/examples/ioClass/hd44780_I2Cexp

This will check your connections and detect the display for you and give you the information necessary to incorporate it into your own programs.

13

ok,

thats a lot of tipps more
in breadbord-situation all worked fine

but now i am sure to get it to run in practical situation,
only was unsure at wiring..

thanks !

14

In my Reply #3, I was trying to tell that the I2C bus might not be the "bus" that you think it is.
Can you tell how long the distance is to the display, what kind of wires or cables you use, are there pullup resistors, maybe other things on that same I2C bus, and so on ?

15

hi,

the distance between arduino nano and display is about 1,2 meters,
in a 4-wire-cable (GND,VCC,SCL,SDA) like connector pins at display.

That is because the unit with several electronic control parts had to be mounted
separate from the front panel of model railway table ; I didnt await this can be a problem !?

16

That can be a problem.
The SCL may not be next to the SDA wire, it is not that kind of "bus".
The GND should start at the Arduino board, and end at the LCD display and should not be connected to something else (something else that can inject current spikes).
The lower the value of the pullup resistors, the lower impedance the I2C bus is, and thus less trouble with noise. But the sink current (to pull SDA or SCL low) may not exceed 3 mA.
If you use tyraps and tie the I2C signals together with signals to motors, then it will not work.
There is much, much more, and you need to do everything just right to get the I2C bus 1.2 meters further. It is not that kind of "bus".

17

The I2CexpDiag will also print out the pins used for SDA and SCL so you can verify how to wire up the i2c signal wires.

You don't need to have a device attached to get the pin information.

--- bill

18

ok,
you are right with "long distance messaging" by the lcd-display !
As i connected it directly to the ardiuno, letters are showed : ok !

Ardiuno is connected to same power as display.

mysterious : switching off and on power for a minute,
letters disappaered but now are not shown, only a white block
like as connected over distance.
Even repeating power off/on : no letters !

Connecting with the pc-breadboard unit : display works fine

oh oh such complex problems simply to show text on a display ?

i could accept to mount an additional arduino near the display..
but how to communicate between the arduino's ?
And then should i mount an additional power- supply there ?

19

may i have to explain the situations here

1.) pc-breadboard unit : arduino mounted on a socket and is directly
connected and powered by pc

2.) model-railway : several electronic cards are mounted together
with the arduino-socket-card and power-supply, 5V common-line
until now

as written some post earlier in this thread, i should use special power
lines for arduino in general and display-unit..

20

Because the distance is about 1.2m, you use SPI or SUART Port (Software UART Port) between the Arduinos. Connect I2CLCD with the receiver Arduino.
spiUnoNanoz1