Arduino mega2560 + LCD button shield strange A1,A2 ecc readings

Hi there I have: 1) Arduino Mega 2560 2) Keypad shield with 6 buttons that all communicate on analog pin 0 I want to read 4 sensors that put their 4-20mA signal into my A8,A9,A10,A11 with a 250Ohm resistor but everytime I press a button on the shield all the sensor goes down near the expected value of my A0 button.

What is causing that interference? How can I solve it? I've already tried the trick "read twice the analog input and keep the second value".


How is the keypad connected? Power, Ground and signal? How much current does it draw when a button is pushed?

How are the 2.5 kOhm resistors connected to ground? What are the connections to the Mega and what are the connections to the remote sensors? How are the remote sensors powered?

What values do you see when a button is not pushed? what do you see when a button is pushed?

A picture or circuit diagram would be helpful. Code might be helpful.

There should be little or no crosstalk between the low impedance (250 ohm) sensor inputs and the resistor/switch ladder on A0.

No links, nocode, no pictures, no wiring diagram. Should we guess? Leo..