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Topic: Resistor between NodeMCU and LCD display (Read 302 times) previous topic - next topic

Flow000

Hi.

I read many topics about wiring ESP8266 and basic LCD display. It's important use resistor between these things, because NodeMCU has 3V platform and LCD has 5V platform.

But is it still important even if I won't read data from display? When I won't read data, signal will flow only from NodeMCU to display, won't it?

Thanks for reply.

groundFungus



groundFungus

#3
Dec 14, 2018, 10:24 am Last Edit: Dec 14, 2018, 10:25 am by groundFungus
How is the LCD to be interfaced, parallel, I2C, shift register?


groundFungus

#5
Dec 14, 2018, 11:03 am Last Edit: Dec 14, 2018, 11:08 am by groundFungus
The best way, in my opinion, is the bi-directional level shifter with MOSFETS.



You can but level shifter modules as well.  Be sure that they are bi-directional for use with I2C.  Google "bi-directional level shifter" for lots of choices.

ardy_guy

I've been running an I2C LCD like that off a nodeMCU for some months. I power the display off the MCU's 5V pin; it's labelled VV on mine, some boards have different markings, 3rd from top, left side.

MCU's and LCD's I2C pins wired directly together, no level shifting.


Flow000

Thanks, but nobody answers on my question.

"But is it still important even if I won't read data from display? When I won't read data, signal will flow only from NodeMCU to display, won't it?"

groundFungus

With I2C the SDA line is bi-directional.   Signals go both ways.   The ESP sends data out and the LCD acknowledges, so you are actually writing and reading.

bperrybap

With I2C the SDA line is bi-directional.
SCL is also read by the master as the slave can do clock stretching to slow down the clock.

Flow000,
If you want to properly interface a 3v master to a 5v slave you should use a level shifter.
There are ways to cheat but they all are non compliant and may have issues.
Some methods - like directly connecting the 3v master to the 5v slave - risks damaging the 3v master.

The safest method to cheat is to run the slave at 5v but wire the SDA and SCL pullups to 3v.
While this is out of spec and will fail at higher clock rates, it usually works at the default 100 kHZ clock and avoids risk to the 3v master.
Note that this requires eliminating and removing any existing pullups that are connected to 5v that are usually present on i2c LCD backpacks.

--- bill

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