Circuit misfire

Up4Days

Hi I'm currently working my way through What's a Microcontroller with a BS2 Homework board( I believe it's now called the Activity Board). Everything is going great but on project PushbuttonControlOfTwoLeds.bs2 on page 85 I noticed the top switch·controlling left LED·is very sensitive to the point that if my finger is even close it triggers the circuit and even stays stuck on sometimes as well. Coincidently 555 push button circuits (using the same type of switches)·I've built over the years always·react the same way so I wasn't to worried about it, but was wondering if someone had an explanation or a fix or if it's NOP for such a basic·circuit.

As a side note from what I remember I experimented with adding a·common ground·capacitor and messed with·resistor values to make the circuit more stable but I've never really used the circuit probably for this very reason. I'm guessing it's the switches that cause the problem. Any comments or input appreciated, this one has·been bugging me for years.

Especially since I wouldn't want to interface it with a drill press or something for the unexpected start up and finger removal value alone .

Thanks in advance.

$WMc%

Up4Days

It sounds like Your letting the input pin(s) float? I would use a 10kohm PullUP resister for active low "0" on button press.Or PulDown resister for active high "1"

If the input pin is just left to float stray Capacitance could change its logic state. The Human finger has a lot of stray Cap. especially indoors due to the AC wire in the walls of a home or building.

One last thing to mention. Put a 220ohm resister in series with the I/O pin. Just in case the pin was accidentally set to an OUTPUT.
This resister would help protect the pin from a dead short.

_____________$WMc%______

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Truth is out there············································ BoogerWoods, FL. USA