Hi,
I have an LCD screen with a I2C backpack however i am unable to get it to work with an arduino nano. I have used many example sketches, i am using the NewLiquidCrystal library. When i run the hello world example sketch the power led on the backpack flashes very faintly for less than 0.5seconds the backlight doing the same and nothing on the screen. after this the screen and power led stay off.
I have tried: i2c scanner which gives me 0x27 address.
The I2Cexpdiag sketch from Bill Perry. this says there is no I2C device found.
Turning the pot on the backpack and the jumper wires.
A different usb power supply
this is the lcd and backpack:
https://www.amazon.co.uk/gp/product/B07F11H8BZ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
the images attached shows the layout and a very poorly drawn pinout i did by checking for continuity.
Any help is appreciated.
Solder the backpack to the LCD module. Pin #1 (square pad) on the backpack goes to pin #1 on the LCD.
Post a photo of your soldering if you have a problem.
David.
asrelick:
I have tried: i2c scanner which gives me 0x27 address.
The I2Cexpdiag sketch from Bill Perry. this says there is no I2C device found.
That is very peculiar.
Bill Perry has written an improved LiquidCrystal library called "HD44780" which you install from the Library manager in the IDE. Install that and try out the examples provided with that library.
Hi David,
I had already soldered the boards together. I just did a continuity test between the pins of the backpack (presoldered) and the gold contacts on the lcd board (on the back) and everything seems ok. I just redid the soldering, i.e. melting solder again (not adding additional solder) and checked continuity again which seems ok.
However i just powered it up again and now both the backpack power led and lcd backlight flicker a few times before staying off. this flickering is much brighter than before so i assume there must be an issue with my soldering. Is there anything else i can check to verify this? resistance between backpack pins and lcd contacts?
pic attached for info.
Hi Paul,
I have his library installed and have just tried his helloworld sketch for i2c and it still does not work unfortunately.
Well, they are soldered, and they are very close together. Check that nothing - such as the mounting clips of the LCD itself - are touching.
Note: if the pilot or "power" LED on the backpack (often a nuisance, actually) goes off; that is not a software problem as it is not under software control, that is a short circuit! I presume the Nano pilot LED does the same.
one of the mounting clips looks like it is touching or close to touching the ground pin (which goes to the arduino). i have checked for continuity between those and there is nothing so i assume the paint/coating on mounting clip is insulating it. As far as i can see there is nothing else touching.
the LED labelled 'POW' on the nano stays lit and the other LED on the arduino (i guess the pin 13 one) blinks whilst running the helloworld sketch from Bill Perry. It says in the comments on the sketch that it will blink this LED if the LCD fails to initialize.
Could it still be a short circuit if the power LED on the Nano is still lit?
Your soldering "looks" ok.
The backpack pcb should not actually touch the black LCD mounting lugs.
You should be able to slip some paper or thin cardboard between the two pcbs for "safety".
I would expect everything to just work. If faulty, ask for a replacement or a refund.
Only you know whether you have damaged it yourself or whether it was bad from the shop.
The shop will replace / refund.
If the shop is reluctant, always ask Amazon ( Ebay / Aliexpress / ... ) for help.
The shop will refund.
David.
I just soldered up the other LCD and I2C backpack (leaving a larger gap so nothing can touch between the boards) to test it and it behaves in exactly the same way as the first one. It would be very unlikely for both to be faulty although not impossible. It makes me think that perhaps i need to define the pins differently. Do you think these backpacks i have are wired differently compared to what is typical?
Bill Perry's "hd44780" library will detect the I2C address and the wiring.
If your soldering is "respectable", everything will work 100%.
David.
The power LED on the backpack should never go off. If it does, there is a power issue.
It could be due to either a short or bad wires between the backpack and the Arduino.
If the LEDs on the nano are working, then that would seem to point to the wires having issues vs a short as a short would likely pull enough current to cause the USB power to shutdown.
Make sure to check the jumper wires to make sure that they are ok.
You need to be very careful during any testing as a short could cause more damage so you don't want to leave things hooked up for very long.
Do you have a multimeter?
You could check the continuity between the power signals on the backpack.
On mine I get between 3k to 5k ohms. If you get significantly lower than that like close to zero ohms, you would know that there is a short.
You could also measure the voltage at the pins on the Arduino and at the pins on the header on the i2c connector on the backpack and see if there is voltage getting to the backpack.
There is no point in running any other s/w until the diag sketch passes.
Post the actual output from the diag sketch.
Again, you want to do very limited testing for very short periods of time until this is figured out as a short could cause, or already has caused damage, to other/additional components.
--- bill
Thank you all for your help, i now have 2 working LCD screens.
It turns out my soldering on the LCD screens was fine however the same cannot be said for my soldering on the arduino. On the 5v pin, the solder was coming loose and had an intermittent connection. I found this by checking the voltage across the supply lines so thank you Bill for the heads up on that. I can't believe I didn't check that earlier. I suppose I assumed the 5v supply was ok as i had just been successfully using it to power other stuff before trying this LCD screen. School boy error!
Thanks again for your help.
Dan
It is often the simple stuff that trips us up.
Glad it is now working.
--- bill