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I got a small LCD and I would like to power it to show the LCD crystals turning to black.

I would like to show at which voltage the LCD crystals start to turn black.

I did some research about LCD and I saw I probably have to power it with square wave.

Do you have any idea of how I could create a square wave from a DC voltage using basic components?

I saw it could work with a NE555 chip but I don't have this one and I think it could be done in a circuit with simpler components.

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  • \$\begingroup\$ Then you better list what components you do have that you feel might be suitable. \$\endgroup\$
    – Andy aka
    Commented May 17, 2018 at 12:19
  • \$\begingroup\$ simpler than a 555? You can wire 2 transistors as an "astable multivibrator" (that'll easily find schematics). Oh and ... LCD crystals never turn black. They change the polarisation of light, such that polarised filters stop it. \$\endgroup\$
    – user16324
    Commented May 17, 2018 at 12:21
  • \$\begingroup\$ Transitors mosfet and bipolar (npn, pnp), capacitors, resistors, diodes, opamp, etc ... but may be it's simple to just buy this NE555 chip, I don't know. \$\endgroup\$
    – A.Girafe
    Commented May 17, 2018 at 12:23
  • \$\begingroup\$ Thank you @BrianDrummond, I will search for an astable multivibrator circuit then ! \$\endgroup\$
    – A.Girafe
    Commented May 17, 2018 at 12:29

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To properly turn on the elements of an LCD you need a signal which has (on average) no DC voltage. So a clock and the inverted version of the clock would be a solution. The simplest way to make those I can think of is with Schmitt-trigger inverters:

schematic

simulate this circuit – Schematic created using CircuitLab

I select Schmitt-trigger inverters because then you only need a resistor and a capacitor to make an oscillator.

Note that you can also make a Schmitt-trigger inverter from other Schmitt-trigger gates like Schmitt-trigger NAND gates in a CD4093 chip.

The LCD elements must be connected between clk and clkn

You can also use an NE555 but then there's no inverterted clk signal. A solution for that would be to make a 1/2 Vdd voltage using two equal value resistors. Then connect the LCD element between 1/2 Vdd and the NE555's output.

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