Smart Keypad Adapter


The LC-075 Smart Keypad Adapter module simplifies the use of 3×4 or 4×4 dome keypad matrix modules with microcontrollers or SBCs like Arduino and Raspberry Pi. The LC-075 is designed to achieve 3 important results:

  1. Reduce pin usage from 7-8 pins to 1-2 pins
  2. Simplify programming with analog voltage output, I2C or UART(“Serial”) outputs
  3. Reduce code footprint – no libraries required. 


  • 3.3-5V input power and logic operation
  • Only 1 or 2 pins required from host
  • 3 outputs: Analog Voltage, I2C and UART (Serial)
  • Reverse polarity protection
  • Low power consumption < 30mA
  • Simple programming – no library required
  • Compatible with Arduino/Raspberry Pi


The module has a 4 pin 2.54mm pitched header with the following functions.

Pin LabelFunction/Operation/Remarks
VCC3.3Vdc to 5Vdc power input pin.
GNDGround pin.
A00-2.5V analog voltage output pin. The output voltage corresponds to key pressed and is distributed equally throughout the range.
SCL/RXShared pin with I2C SCL and UART receive signal. See SELECTING I2C OR UART MODE Section. In UART mode, this pin is reserved for the future.
SDA/TXShared pin with I2C SDA and UART transmit. See SELECTING I2C OR UART MODE Section.


  1. Remove power.
  2. Insert a 3×4 or 4×4 matrix keypad in the assigned pin header
  3. Press and hold the * and 4 key for UART/”Serial” mode or * and 1 for I2C mode
  4. Apply power while still holding the key combination selected.
  5. After one second, from power up, release the keys.
  6. Power cycle or reset the host microcontroller
  7. Done. Test to confirm. Repeat if operation failed.


Follow indicated installation area labelled on the board.

4×3 keypads are installed between R1 and C3 pins and facing up. While 4×4 keypads are installed between R1 and C4 and also facing up. See figure 2 for details.