I have a Arduino Mini Pro 3.3V and feeds it with 5V to "RAW" which converts it to 3.3V. I want to run a LCD screen but the backlight seems to be needing 5V. Can I connect the LCD VCC directly to my 5V source (GND, SDA & SCL still connected to the Arduino) or will that cause trouble elsewhere?
Please post a link to the actual screen that you have bought.
We need to see a picture of the pcb to identify it correctly.
Then we can give an accurate answer.
David.
The screen data sheet should tell you logic levels, most screens have level shifters, check the data sheet for yours
Get a 5V I2C display.
Put a logic level converter in the SCL/SDA lines.
Go on. Can you expect an Arduino user to know what a datasheet is ?
But you can expect them to know what a picture of a pcb is.
A picture is worth a 1000 words. And if the OP is a non-English speaker it avoids any "Google Translate".
Can you expect them to have a camera ?
But most will be able to find the sale page of an item that they bought on the Internet.
Or to find a "similar looking" item on Ebay, AliExpress, ... that they could link to.
David.
Unlike you, I don't expect an Arduino user to be a stupid, illiterate monkey. Did this answer your question? Never reply to me again please.
Ok. Please find the appropriate datasheet for the item that abbesnabb has on his desk.
Or even the datasheet for any I2C LCD that you possess. Then I will give you an accurate answer.
No, I don't think that members are stupid or illiterate. But not everyone is technical and not everyone is an English speaker. But pictures explain things well.
Most importantly, we can give practical advice that might mean the user does not need to buy any extra components.
David.
These SSD1306, OLED 128X64 displays are inexpensive (~ $3.00) easy to use and can operate on either 3V3 or 5V.
Yes, the pcb in your picture can operate with 3.3V - 5V on the VCC pin.
Not all SSD1306 OLED displays contain an AMS1117-3.3 regulator ( U1 on your pcb picture)
Which is why it is a good idea (tm) to post a link (or photo).
David.
We know the OP is aware there are 5V and 3V3 Arduinos therefore they would be fully aware the SSD1306 display they buy needs to match the Arduino board they have.
The OP is asking about an LCD with backlight.
I am guessing that it is a 16x2 with a PCF8574 backpack. You are guessing that the OP has an OLED which does not have a backlight.
It might even be a TFT LCD.
Which is why a picture would eliminate any guesswork. And a link would show whether it is a backpack with or without pullups. And show the PCF8574 connecions.
David.
I was offering the OP an alternative that they might be unaware of or didn't think of.
If the OP chooses to ignore the post they can easily do so.
The screen is a LCD display 2x16 1602 with a serial to parallell interface. The LCD display is described as Model:SMR1602-A and according to the data sheet it runs on 5 Volts. Nothing mentioned about level shifting.
Perhaps what I want to do can be achieved with a signal adapter?
(I was hoping that I could just run 5V straight to VCC on the LCD but perhaps that is not possible).
I think I understand now that feeding the LCD 5V would send 5V right back to the Arduino with the signal wires which in this case would be bad.
Not if you are using a 5v Arduino
For a 3V3 Arduino:
Yes, that looks like a good logic level converter to use with your I2C lines.
i.e. 3V3 to 5V logic levels.
Thanks for the photos. They show exactly what items you have on your desk.
The PCF8574 backpacks are intended for a 5V 16x2 module.
The blue potentiometer provides a suitable voltage to control the 16x2 contrast pin.
The PCF8574 switches the 16x2 backlight via a transistor.
The 16x2 controller works fine with 3.3V. But you can't set a suitable contrast with 3.3V.
There are two practical solutions.
- remove the pullups from the backpack pcb. Use external pullup resistors to 3.3V. Connect VCC pin to 5V.
- Connect LV1, LV2 to Pro Mini. LV = 3.3V. Connect HV1, HV2 to backpack. HV = VCC = 5V.
(1) should work ok but involves un-soldering SMD resistors and buying external resistors.
(2) is the easiest solution. you already possess the level-shifter module. no soldering involved.
David.
p.s. the photos were important. some backpacks come without pullup resistors which means no un-soldering.
Or
- Swap to a 5V Pro Mini. Save the 3.3V Pro Mini for a project where no 5V supply is available, like a battery powered project for example.
My approach to this Forum is :
the member asks a question, provides links to her hardware.
we offer solutions based on the existing hardware.
In an ideal world. The "answer" works. The OP's problem is solved.
Generally in software. Sometimes with a wiring "correction"
Of course, the advice might be : buy some extra hardware. e.g. resistors, capacitors.
Or worse : buy completely different hardware.
I always bang on about providing links or photos.
If the OP spends 10 minutes composing the original question it avoids members guessing or asking for extra information.
And the OP might get a solution within a few minutes / hours.
Any advice that involves "buying hardware" means days / weeks for internet purchases.
Or significant time and effort to visit a local shop.
Yes, the "different hardware" advice is useful to other readers.
But "how to using existing items" is what the OP wants to know.
David.
1 Like
Maybe @abbesnabb already has a 5V Pro Mini. After all, they had a logic level converter. Most beginners do not have such a thing and wouldn't know what to use one for. And the 5V version is much more common and often cheaper.
Please don't feel the need to defend your approach to the forum with me. I found @killzone_kid 's "never reply to me again" request somewhat surprising. We are all allowed our opinions. We should all be prepared to have our opinions questioned from time to time. It's a healthy discussion.
[quote="PaulRB, post:19, topic:1021885"] I found @killzone_kid 's "never reply to me again" request somewhat surprising
[/quote]
No surprise, the user has been targeting me with nonsense questions. You can hardly call it healthy discussion. Anyway, no point discussing it further, it’s done and dusted