Oscilloscope Display from Nokia 3310 LCD

The project illustrates the interfacing of Nokia 3310 LCD to create a simple scope that would display low frequency sine wave.

The interfacing of display utilizes serial interface with the reduction of LCD voltage to 3V level when using 5V logic. This can be achieved by using 2 general purpose diodes connected in series that will provide around 1.4V drop to develop 3.6V across R1. This project is a new design which includes brown-out protection and 20×4 or 16×2 LCD bus interface. The new straight cable for RS232 interface is male type DB9 on both ends. A cross cable was used instead, in the original version.

There are two 4.7K resistors connected in series to function as a simple level shifter for the AC input signal where one end is tied to +5V and the other end to the AC signal. The input current is limited by the resistors R2-R6 from 5V to 3V logic.

In the old design, there is a 5V voltage regulator and a protection diode. The level converter for RS232 is MAX232 while the RS485 is the transceiver. The two channels of analog input has RC filter connected.

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