The strangest thing.

Hi,
have just been playing with a microcontroller (PIC24FJ64GA006) and
was working on getting external interrupts going, I have a small bread
board and the chip is on a small PCB with wires comming out to connect
to bread board, well I noticed that the wire connected to INT1 pin
trigers an interrupt if my hand gets near to the wire, like 1 cm away,
you can set of the interrupt with out even touching the wire, any
ideas what is going on here, its very strange.

Thanks

 

[Stephen J. Rush]

On Sat, 28 Jul 2007 10:29:03 -0700, RichardJHarris2 wrote:

Hi,
have just been playing with a microcontroller (PIC24FJ64GA006) and
was working on getting external interrupts going, I have a small bread
board and the chip is on a small PCB with wires comming out to connect
to bread board, well I noticed that the wire connected to INT1 pin
trigers an interrupt if my hand gets near to the wire, like 1 cm away,
you can set of the interrupt with out even touching the wire, any
ideas what is going on here, its very strange.

Your body is acting as a capacitor, coupling the powerline hum into the
high-impedance input of the chip. This is how most touch-operated light
switches work. To make a switch that you have to actually touch, a shunt
resistor desensitizes the input.

 

[John Fields]

On Sat, 28 Jul 2007 10:29:03 -0700, RichardJHarris2@gmail.com wrote:

Hi,
have just been playing with a microcontroller (PIC24FJ64GA006) and
was working on getting external interrupts going, I have a small bread
board and the chip is on a small PCB with wires comming out to connect
to bread board, well I noticed that the wire connected to INT1 pin
trigers an interrupt if my hand gets near to the wire, like 1 cm away,
you can set of the interrupt with out even touching the wire, any
ideas what is going on here, its very strange.

---
CMOS inputs are not allowed to float.


--
JF

 

[JeffM]

RichardJHarris2@ gmail.com wrote:

can set [off] the interrupt with out even touching the wire,

http://www.google.com/search?q=cache:NJ-NAWTu8XoJ:en.wikipedia.org/wiki/Pull-up_resistor+Pull-up.resistors+501+pull.down.*

 

[Jasen Betts]

On 2007-07-28, RichardJHarris2@gmail.com <RichardJHarris2@gmail.com> wrote:

Hi,
have just been playing with a microcontroller (PIC24FJ64GA006) and
was working on getting external interrupts going, I have a small bread
board and the chip is on a small PCB with wires comming out to connect
to bread board, well I noticed that the wire connected to INT1 pin
trigers an interrupt if my hand gets near to the wire, like 1 cm away,
you can set of the interrupt with out even touching the wire, any
ideas what is going on here, its very strange.

it's resopnding to the mains hum in your body. (you know how you get a
humm sound if you tuc the cente of a phono input on an amplifier)

Bye.
Jasen