Using 5v LCD with Teensy (3.3V input/output)

Using Arduino Displays
1

Hi,

I am planning to use an LCD screen in a project to display values of encoders as they change. My worry is that I am using an external 5v supply to power the LCD, but the teensy will be connected via SDA and SCL pins for comms, so will these pins use 5v as this would fry the teensy ? (This is LCD being used FREENOVE I2C LCD 1602 Module, New Type IIC TWI Serial 16x2 Display, Compatible with Arduino Raspberry Pi Pico ESP32 ESP8266 : Amazon.co.uk: Computers & Accessories)

I have seen a range of solutions/opinions on this on forums, such as buying level shifters to be safe, but this isnt really ideal as I have 16+ encoders so that will be a lot of extra parts. Is it just worth buying another LCD compatible with 3.3v instead ?

Thankyou for the help.

2

You only need one level shifter

With this board you can use two of the three I2C busses

3

imho yes, just buy a dedicated 3V3 LCD.

4

I simply connect the pull up resistors to the 3V3 and run the display etc at 5V. things work OK. If my memory is close a logic zero is about 1.1 volts on the I2C bus.

2 Likes
5

There can be issues doing that, particularly if the slave already has pullups on it to 5V.

1 Like
6

If they have pull up resistors they probably are 10K to 5V. That would drive 0.17 mA through the 3V3 protection diodes, well within tolerance. The op did not mention any other devices on the bus. If it is a worry the pull up resistors can be disabled or removed on the module. A lot simpler then adding more parts and chances for an oops.