adc interference

[naveed1978]

Dear Friends

i have designed a data acquisition card using PIC18F452. i read 4-20mA signal transmitted by Temperature transmitter and the correspoing reading is displayed on 16*2 LCD Screen interfaced with PIC. i have also a wireless base unit in my workshop for communication so when i turn on the base unit PIC ADC gets some signal from it and displays erronious signal on the screen.
any one can help me how to get rid from it.
Thanks

 

[mitz]

Although not so sure of the problem, I try to give my thoughts. Floating MCU pin can pick up signal from adjacent pin. ADC section can be shielded for RF interference.

 

[mitz]

Blocking HF interference
DC-motors without filters and other devices containing large coils can generate strong high frequency signals. Those can potentially interfere with the LCD display electronics. The result can be funny characters on the display. The microcontroller itself is not so sensitive as it is mostly self contained. The interference depends also to a large degree on how the internal wiring inside the case of the power supply is done. Longer cables between display and circuit board act as antennas which can easily pick-up HF signals. In any case the best solution is to block HF signals directly at the front connector of the power supply.

Solder a ceramic capacitor in the range of 10nF to 100nF directly behind front connectors.

A ceramic capacitor between the power output connectors to block HF-signals from coming into the power supply.

Portion of the article with the link below is given for your reference
http://tuxgraphics.org/electronics/200707/bench-power-supply-unit.shtml