Accessing and Modifying LCD Output on Microcontrollers in Calculators and Microwaves

Good day all,

I really enjoy taking stuff apart and then putting it back together.

I've been reading about the components of low level devices which have LCD screens.
I've been researching what makes the numbers on the screen.

I'm especially interested in accessing the coding database on microcontrollers (?) so I can see my microwave go something like 10-9-8-3-6-2-4-1-2-9 Beep! Or pressing 5 on a calculator and seeing 7 appear!

Must I need to know C? Is the output of LCD screens accessible/encrypted on basic electronics such as calculators?

Hi Alex

You have grouped a vast number of different displays under "LCD Screens".

With some of these you can do what you have in mind, with others it is not that easy.

The ones you can do this with (fairly easily) is 7-segment displays sometimes
found on microwave ovens etc. The logic levels on the display lines indicate what is
displayed. There are also segmented displays you may be able to do this with.

Other LCD displays have a controller chip which sets the logic levels on rows and columns to change the display contents, with these it is much harder/impossible. Often you cannot access the row and column connections easily. This includes character LCD displays, i.e. the 16 character by 2 line displays etc.

Depending on what your want to do, you don't need to know C. I recommend starting with some Arduino projects first.

A word of warning. Most electrical equipment with the displays you want to connect to contain dangerous voltages (even when turned off and unplugged) that can kill you. Best you stay clear of these units.

Hi Pieter!

I am interested in 7-segment display screens on low level devices such as calculators, scales watches etc. I am not going to be opening up my microwave straight away!

When you say 'fairly easy' what actually is involved?

Any response would be hugely appreciated!

Regards

Alex

Hi Alex

By Fairly easy, I mean the logic is available, i.e. you can access the display pins easily. In a calculator it is a little harder. Another thing to keep in mind is that usually when you have multiple 7-segment displays, they are multiplexed to save on IO pins. In other words, each display is turned on for a short time and the logic lines (which determine what is being displayed) are used for each display in turn. Depending on what you want to do (i.e what you want to do with the display data) you either have to connect some sort of latch to each display to latch the data for that display OR have a small Arduino/microcontroller connected to the logic lines to latch the data for each display in turn. (Hope that makes sense.) Depending on the frequency used for multiplexing (~50Hz) you may be able to see a flashing effect our of the corner of your eye when looking at the display / otherwise you would have to connect an oscilloscope to see if the display is multiplexed.

Also, keep in mind that 7-segment displays are either common anode (i.e. common positive and the logic lines are grounded to turn on a segment) or common cathode (i.e. common negative meaning a high on the logic lines turns on a segment.)

Good luck

Pieter.