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Electronics Forum / Electronics / July 2007The 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 On Sat, 28 Jul 2007 10:29:03 -0700, RichardJHarris2 wrote: > Hi, > have just been playing with a microcontroller (PIC24FJ64GA006) and [quoted text clipped - 4 lines] > 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. >Hi, > have just been playing with a microcontroller (PIC24FJ64GA006) and [quoted text clipped - 4 lines] >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.  SignatureJF RichardJHarris2@ gmail.com wrote: >[...]microcontroller[...]if my hand gets near to the wire[...] >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.* > Hi, > have just been playing with a microcontroller (PIC24FJ64GA006) and [quoted text clipped - 4 lines] > 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 |
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