I have an old monochrome LCD panel that I removed from a calculator. The LCD panel has no standard input pins, because it's directly connected to a driver on which the calculator software runs.

Is it possible to run the LCD without the calculator software? All pins of the LCD would be available (marked in blue). The pins marked in red were connected to the keyboard of the calculator.

Image shows old calculator monochrome LCD circuit

  • Depending on what it is you want to do with it; you could connect the Arduino to the keypad pins, and have the Arduino "type" the number you want to show. Though it's a bit more tricky than that, since the keypad is a matrix, so you'd have to time the fake button presses, so it's in sync with the calculator scanning the button matrix. – Gerben Feb 17 at 16:23
  • google lcd driver waveforms to get an idea of the kinds of signals you would have to generate .... here is one example aardvarklabs.files.wordpress.com/2013/04/waveforms.png ..... the problem with LCDs is that you cannot have a net voltage across a display element ... all the voltages placed across an element over a period of time must add up to zero ... the duration of positive voltages and the duration of negative voltages have to be equal, otherwise the display element will become damaged – jsotola Feb 17 at 18:49

Normally such LCDs are custom designed, mass produced displays especially for this calculator product. Thus it is very unlikely to find a datasheet or even a meaningful part number for it.

Most likely the pins on the LCD are directly connected to the corresponding fields on the LCD. In an LCD you have liquid crystals between two electrodes, which change their orientation, when a voltage is applied to the electrodes, which changes the light absorption of the layer. You need to apply the correct voltage to a pair of pins to activate their field. Most likely all of the fields or a few groups of them have a common electrode (which would be 1 pin). Without any documentation you are bound to experiment with the display, until you have found the correct voltages and pin arrangements. You might break the display in the process (for example through excess voltage).

I haven't done this myself, but googling gives an interesting result:

  • This project, where they hacked the LCD of a cheap calculator for a waveform generator (though the display seems to be way less complex than yours) They seem to use 1.5V as voltage, so this might be a good starting point.

Your display has many pins. Depending on the Arduino model, that you use, you will fast run out of pins to use. You can try arranging the pins into a matrix, which would mean multiplexing the fields (turning them on and off fast one after another). Or you can buy additional parts to extent your pin count, for example shift registers.

As jsotola wrote in the comments (and as several forum threads on web web state), you should not put a constant voltage onto the display, since this will damage it. (I guess the liquid crystals will degrade fast because of their polarity, which make the work in the first place). Instead you have to place an alternating voltage at the pins, which changes it's polarity. The net voltage (The integrated voltage over time) must be zero. Thus you need to alternate the applied voltage. If you provide a span of 1.5V, you need to change between +0.75V and -0.75V.

As the display shouldn't need too much current and the voltage requirement is relative to the LCD ground, you might get way by setting the LCDs ground with a voltage divider to 2.5V and then operating around that. Though I'm not sure about that.

Otherwise you might need to actually change the polarity. This would also just need 1 extra digital output pin as the ground pin. One polarity would be the LCDs ground pin to Arduino's ground (outputting LOW at the digital pin) and the other pins to the needed positive voltage (HIGH divided down over a voltage divider or similar). The other polarity would be LCDs ground pin to the needed positive voltage (HIGH divided down over voltage divider) and the other pins to ground (outputting LOW).

As described above, hooking this bare LCD to the Arduino is not done fast and easy. You can try it, if you like to do it. But if you want to get your project (whatever it is) done fast, you should instead buy a LCD with integrated controller, which are mostly ready to use, and for which there are already libraries.

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In theory, maybe yes, in practice it will be hard job.

Some things you need to find out:

  • Find the exact model of the LCD
  • Find its datasheet
  • I see an enormous amount of pins (especially the blue ones), so you need (a lot of) multiplexers or shift registers.
  • Speed of the Arduino, is it enough to drive this LCD?
  • You have to solder this to test.
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