Floating Makes Me Nervous

[bumba000]

Hello All,
I have the ProTrinket. I'm using pin10 to drive n-mosfet at specific times using analogWrite(10, someval);. Just for kicks I'm doing an anologRead on 10 when it's not in use and it's showing anywhere from 100 to 900 (floating??).

Does this mean that even when I'm not using pin10 it's still signaling the mosfet or am I just getting a reading of like static elec from around the board? Any way to stop this from happening?

Measuring pin10 with a volt meter it reads zero, but the mosfet reads 3.9v.

Thank You, John

[zener]

Some questions and comments:

Why are you doing that and what did you expect to read?

Sometimes the first ad read is bad. I usually average

You would need to turn the pin back into an input for that to work at all I think.

The fet gate is a capacitor. You need a pull down resistor or drive it low to turn it off.

[bumba000]

I did it just to see what pin 10's value would be if not set at all. So a pulldown huh? I'm having a bit of trouble understanding this. If I connect the gate of the mosfet to pin10 and connect that to a resistor to ground, what happens when I want to drive the mosfet? Does all of the driving signal/power go to the mosfet because it's easier than going to ground??

Thank You, John

[zener]

The io pin can source an amount of current up to around 20 ma I think. As long as the resistor value is large enough (10k is typical) then it has no trouble driving the voltage high. The mosfet gate requires essentially no current, other than a little to charge the very small gate capacitance.