Liquid-Crystal Display (LCD) Tester


Posted on Feb 5, 2014

A segment may be tested by applying an alternating voltage of a few volts across it. Note that the application of a direct voltage will damage the display irreversibly: the resulting current will remove the tracks. The alternating voltage should contain not even a tiny direct voltage component. An alternating current also removes part of the tracks when the current flows in one


Liquid-Crystal Display (LCD) Tester
Click here to download the full size of the above Circuit.

direction, but restores it when the current flows in the opposite direction. The tester described here consists of a square-wave generator that produces an absolutely symmetrical alternating voltage without any d. c. component. Most logic oscillators are incapable of producing a squarewave signal: they generate rectangular waveforms whose duty cycle hovers around the 50%. The 4047 used in the tester has a binary scaler at its output that guarantees symmetry. The oscillator frequency is about 1 kHz. It may be powered from a 3 9 V source. Normally, this will be a battery, but a variable power supply has advantages. It shows at which voltage the display works satisfactorily and also that there is a clear relationship between the level of the voltage and the angle at which the display is clearly legible. The tester draws a current not exceeding 1 mA. The test voltage must at all times be connected between the common terminal, that is, the back plane, and one of the segments. If it is not known which of the terminals is the back plane, connect one probe of the tester to a segment and the other successively to all the other terminals until the segment becomes visible. Note, however, that there are LCDs with more than one back plane. Therefore, if a segment does not become visible, investigate whether the display has a second back plane terminal.




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    12V voltage doubler circuit
    Laser Communication (Transmitter
    LDR Pole Light Switch
    tesla coil
    AD Design
    How to test a triac
    Mini efficient coil launcher from disposable camera flash
    Emitter-Coupled LC Oscillator
    DTMF decoder using MT8870DE



    Top