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Toys with a LCD
This is not a "how-to" it is more of a "reasons for limitations" in hopes of sparking another approuch. Now I am not an expert this information is based on my observations.
While breadboarding different osc I tried each setup (555,2 inv, LTC1977) on 4 toys. 2 of the toys had LCD displays a Vtech Talking Whiz Kid and a Vtech Picture Alphabet Desk. This info is not skewed by both being Vtech toys because a toys LCD is controlled by factors beyond any possible proprietary code on a chip.
Here is a brief overview.
The LCD complicates the entire circuitry, duh. The cpu/mcu/however you want to refer to it has to generate the audio, generate the visual, and sync the visual to audio.
Generating the audio - this is not going to be too different than any toy without a display.
Generating the visual - Different LCDs have different levels of complexity. Pretty much there are 3 monochromatic LCDs which I would list in order of simple to complex - Picture, 7 segment, and Animated (individual pixels).
Picture LCDs would be like cheap Happy Meal games or Tiger Electronics handheld toys. You can see the image when it is not even "ON".
7 segement LCDs are in calculator, microwave oven, and digital watch displays. These function like 7 segemnt LEDs.
Animated LCDs are made up of rows and columns, yup a matrix, and each pixel is turned "ON" individually.
Color LCDs such as on cellphones, laptops, TVs, and flat panel monitors are even more complex because of mixing and varying brightness of pixels of primary colors. Howstuffworks' How LCDs Work is a good resource, which I am not trying to duplicate but pick out what pertains to displays on toys, which veers towards monitor displays.
Syncing visual to audio - Complexity depends on the number of modes a toy has. A bouncing apple could be used for say "Letters", "Missing Letter", and "Find the Letter". Those are made up examples just to show the same image with different focus of mode and different vocals/audio.
Removing the LCD from pcb does not remove its affect on the toy. There is no sensing capability for the cpu/mcu to operate differently based on presence of LCD.
What about the display on S&*? Those are a fluorescent display which function like 7 segemnt LEDs, so they are not very complex.