PIC affected by human hands??

buckeyes1997 · Joined: 12 May 2005 Posts: 15

Hello
i have a project that works fine and does what its supposed to do, but it seems that whenever i pass my hand near the PIC it turns off. I know that PIC pins that are left floating will go high when a hand is brought near the pins but this is strange. I have one pin im monitoring as an input and its low most of the time. when i turn the device on it works until i pass my hand near it and then it turns off. the condition is that when it reads a high (caused by a human hand) it turns off an LED. its like this think is reading either an input from the input device or from my hand. how can i make it more stable? could the other pins that are not used be a problem?? should i make all unused pins outputs or inputs or something?

thanks

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Somewhere on your project, you've left off a ground connection
or you've got floating input pins, or a combination of the two.

You can take all unused pins and set them to be low level outputs.
For example, if you're not using Pin E0, then do this:

output_low(PIN_E0);

This assumes that you're using the CCS standard i/o mode,
in which the TRIS is handled by the compiler.

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

your missing a pullup resistor.
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buckeyes1997 · Joined: 12 May 2005 Posts: 15

hey everyone thanks for helping.

im not sure what i should be grounding other than the PIC. i dont have a cap across the rails, but the input is 5v digital so should be fairly clean. the pins that are not in use are not tied to ground or high they just arent connected to anything. i dont use pullups because i have the weak pullups turned on. i shouldnt need an additional pull up right?

my next step was to try using output_low(pins) at boot and see if that fixes them. im just worried because the only pin that is even used in the program is in input, so if its the other pins that are the problem i dont understand why since i never use them in my code.

thanks for any suggestions.

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

You should always put 0.1uf caps as close to the power pins to most all IC's. But this isn't the cause of your problem. Make sure all your power and grounds are connected. Also check your oscillator circuit.

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands