[SOLVED] is it possible to connect adc i/p and lcd data to same pin?

[welove8051]

hello everyone, consider the following condition. we are going to share a ADC pin for measuring analog signal as well using it as digital output to LCD data pin.

for ADC i/p to mc:
will the LCD data pin act as load or will it be in high impedance state?

for LCD i/p from mc:
will the analog input affect the lcd operation?

please share your views.

 

[FvM]

I presume you are using a processor with shared analog/digital pins, e.g. a PIC.

for ADC i/p to mc:
will the LCD data pin act as load or will it be in high impedance state?

It's high impedance as long as it isn't enabled for read operation.

for LCD i/p from mc:
will the analog input affect the lcd operation?

Basically yes. You'll need a series resistor for the analog source to allow LCD operation. The resistor will possibly reduce ADC accuracy. A value of 1 to 2 k may be appropriate.

If your application uses readback from LCD, the pin configuration must be switched back to digital during read operation. If you don't read digital data from the pin, it can stay in analog mode.

 

[welove8051]

where can i find the information about lcd pin impedance? does the datasheet gives any information about that.

 

[FvM]

Yes, leakage currents are specified. Original HD44780 has weak pull-up resistor which will cause a DC offset. There are of course various options to isolate analog and digital by analog multiplexers or digital buffers.