Numerical LCD With Built-in RTC for Arduino

Extensive resources are available to the applications of dot matrix LCD s. This instruction is about EM32117, a numeric LCD with built-in RTC (Real Time Clock) with simple serial interface to Arduino. The operating voltage is just 1.5V with only 4uA power consumption. EM32117 is one member of EM32110 series. This application applies other members as the communication protocol is the same, the variations apply other features such as number of digits of the driver. Read application note for details.

This component may not be available in the market, but you can get it from a landline telephone with LCD, corded or cordless, if you are lucky, as the LCD driver is designed to direct interface to telephone dialers from ELAN Microelectronics Corporation.

1. LCD module with EM3211x built-in driver.
2. Arduino Board, I am using UNO R3.
3. General tools for electronics PCB work.
4. Application Note for the LCD driver as attached herewith.

If you can not get it from market place, you can remove it from a landline phone. To identify the LCD driver, you had to check the prints on the module, or if the dialer chip is from ELAN. The dialer from ELAN is normally prefixed with EM followed by digital numbers.

The key pins for this project are Power and Ground, HKS and SDI. If you cannot find them from the silk print on PCB, you can trace it by the connections to the dialer chip, if you have data sheet or application note for the dialer by hand.

If you know it works before removing from your phone, you can skip this step.

Power Up Test: Connect a 1.5V power supply to the Vdd and Vss pins, it should has numeric display the clock or stopwatch.

Serial Data Input Test: Set HKS pin to LOW and short the SDI to TEST pin, digits and icons should display in sequence. Read the application note for details.

Power Source: EM32117 operates at 1.5V while Arduino is normally power by 5V. You can use voltage step down converter or regulator to obtain stable 1.5V power from the 5V, or configure a voltage divider. I am using a 1.5V battery.

Level Shifter: The configuration is the same as of a voltage divider between the 5V logic to 1.5V one. Take two resistors, the one connecting the output of Arduino to the input of LCD is R, and the one from the LCD input to Ground is Rg, the criteria to chose R and Rg is:

Vlcd = V * Rg /(R + Rg)

then R/Rg = (V - Vlcd)/ Vlcd

In my case, V = 5V, R = 10k, and Rg=4.7k. Four resistors are used as only HKS and SDI pins are applicable for the test.

The HKS pin is equivalent to a Data Enable for serial data interfacing, unfortunately hardware serial port doesn't support baud rate as low as 256, as the application note designated, nor the soft serial library. The testing code employs bit bang method to implement serial date transmission. Start Bit and Stop Bit are packed with data bit for the simplicity.

See video for the demo and project on GitHub.