LED glows when hand close to breadboard

[gabeNC]

Howdy,

I've got a 16F876a on a breadboard, and working through Nigel's tutorials. So far so good, first couple work fine. Kinda strange, when my hand gets within about 6 inches of the breadboard one of the LEDs starts to glow (the one that the switch controls). At first I thought it might of been the Pickit2 powering the circuit and maybe the BB too close to the laptop but now i'm running it through a wall-wart and a 7805 regulator.

I'm sure it's something stupid.


thanks gents!

 

[Pommie]

My guess would be that you don't have a pullup on your switch.

Mike.

 

[gabeNC]

Thanks for the reply Pommie: I've got (2) 4.7K resistors in series (cause i don't have a 10K ) on the switch.

Okay a little disclaimer here... I recycled the switch from another PCB i had laying around. Ended up using a dremel cut a nice square and keep all four switches together in one piece. It's probably 2x2 inches. Soldered wires on the back, used a multi-meter to make sure they are isolated from each other and no shorts. Looking closely at it, I noticed a ground plane around this chunk of the PCB, could it be acting as a antennae? I'll swap out the switch tonight with something else and check that.

 

[ronsimpson]

Hand near board...some thing different...
This happens when some pin is not connected. Try touching +5Volts with one hand and with the other touch every pin, one at a time. If that does not work try touching ground and every pin.
OR
Use a high value resistor (100k, 1M), pull up or down every pin untill you find the notconnected pin.

 

[gabeNC]

I guess this is what they mean by don't leave pins "floating"? Is it possible to set the TRIS registers on each port/pin that you don't need?

thanks.

 

[tresca]

i had a similar problem. It was a static build up and it seems that I was emitted electrostatic force(terminology could be wrong). Anyways, ground yourself. What I did was took my shoes off, and basically touched the floor (hardwood). Led stopped glowing for me.

Maybe thats what your issue is ?

 

[DirtyLude]

That seems like a feature to me. You now have a proximity sensor.

Good work, sir.