PIC I/O responds to transients?

Hai

I have a small control unit using PIC16F72 which has 6 input switches each of which are pulled down using a 100k resistor. When switch is pressed positive potential via a resistor is applied to each pin so that key press is detected.

But when any flouresent tube light or some heavy loads are switched 16F72 senses a key press and acts accordingly. PIC responds mainly to flouresent tube light flickering. PIC is not resetting but it senses key presseses.


Please suggest how to overcome this issue.
Picstudent

Try to put shielding on your PIC and ground it properly, it will be also good to have total isolation of your high voltage side to your low voltage side.

Lower value pull-down resistors may help noise immunity, or, you might try using pull-up resistors and detecting switch low... Perhaps .01-uf cap' on switch to ground may help?

Best luck... Regards, Mike

Hello

To solve this problem you can do one of two options I am going to mention:

1. If your using PORTB, then use its internal pullups, and connect your buttons between PORTB inputs and ground, so that when a button is pressed, you will have that porb pin connected to ground.

2. If you are not using portb, then use external pull up resistors, say 4.7KΩ, and connect the buttons as I mentioned in the 1st option.

The reason for that isas follows:

Capacitors on the supply rail will try to overcome spikes as possible, so that what really occurs is that these caps will pass the high spikes voltages to GND line which causes instability of the PICs operation. Believe or not, passing the spike voltages to GND while port pins are pulled down, will virtually disturb GND potential for a very short periode of time, but so efficient to cause the port pins to saense a HIGH, as if a button is pressed !!

Think about it ,as you are playing with at least 1usec time base

Thats why its recommended to pull up port pins, and connect the btton between port pin and GND.

Good luck