large number of inputs

pattywac

I want to replace an old car LCD display that has broken with one of the oled displays. The LCD has around 75-100 input pins and on average about 30-50% of them are on. Does anyone know of a way to use a smaller number of input pins to detect the signals from the 100 pins? (like using one propeller chip to read all 100 signals) Ive found a few reverse charlieplexing examples but it doesnt seem like it would work for multiple constantly on signals. Is using 3-4 chips and having them communicate the only way to go?

Thanks

Mike Green

Unless you really have your heart set on using this display, I don't recommend it because of the number of leads. There are plenty of relatively cheap LCD displays of all sorts that have a controller mounted on the display itself and already connected via printed wiring on the display. If you really want to do this, you could use serial shift registers like the 74HC595 to provide 8 bits per package. 10-12 packages would be able to feed the LCD panel and you could string the shift registers in series to use only a few I/O pins.

pattywac

I think you misunderstood. I want to get rid of the LCD but the computer controlling it has ~100 outputs that would normally go to the LCD's inputs. I want to take these as inputs to a propeller chip and map all of the inputs to display on one of the OLED displays (and add some other functions).

Mike Green

I did misunderstand, but the issues are still the same. There's an equivalent input shift register, the 74HC165 that provides 8 inputs that can be cascaded. 10 to 13 of these will give you 80-104 inputs. If you run the 74HC165 off 5V, they'll be 5V inputs. If you run it off 3.3V, they'll be 3.3V inputs. You can do level conversions on the former case with just series resistors.

pattywac

Awesome, thanks for the help.

Leon

A single CPLD will replace all those shift registers.

Leon

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