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20x4 LCD

A project log for Desk Buddy

A small device that lets work colleagues know if you'll be at your desk today so they know if they can sit there.

tony-kambourakisTony Kambourakis 05/14/2017 at 01:280 Comments

This Blue 20x4 LCD module supports bidirectional I2C, is reasonably priced and works well with NodeMCU. The I2C support is provided by the attached PCF8574T backpack module. The supply voltage is 5V and the SDA/SLC lines are

The PCF8574 data sheet states in the DC characteristics section that the minimum HIGH level input voltage for SCL and SDA is 0.7 times the supply voltage. This equates to:

As the NodeMCU output is 3.3V a logic level shifter is used to convert the 3.3V to 5V levels.

The LCD is controlled via the following pin assignments:
LCD I2CNodeMCUGPIO
SDAD4GPIO2
SLCD5GPIO14


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