Unknown input

NosePicker

I am trying to learn how to monitor an input pin on a Basic Stamp II. I have it on a test breadboard with a 6v power supply.
I have written several test programs like make an led blink and everything seems to work as expected.
However I wrote this simplt program and had nothing hooked to pin 8 and got the following results:
As you can see the input pin appears to report random values as to if it is high or low with nothing hooked to it at all.
Is this normal?

<<<<< Program code >>>>>

input 8 
checkpin: 
  if IN8 = 0 then ison 
    debug "0," 
    pause 1000 
    goto checkpin 

 
ison: 
  debug "1," 
  pause 1000 
  goto checkpin

<<<<<< Results >>>>>>>

0,0,1,0,1,0,0,1,1,1,0

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Thanks

NosePicker

Mike Green

This is normal. If nothing is connected to an input pin, what you have is a high impedance input stage with a threshold of maybe 1.5V. Any voltage on that pin above that gets read as a one. Anything below that gets read as a zero. This input is extremely sensitive to static potentials, induced currents from adjacent wiring, the phase of the moon, etc.

DJSandberg

NP,

If you put a 10,000 ohm resister from IN 8 to ground, this will give you 0,0,0,0,0,0,0,0.· If you hook the resister to +Voltage, you will get 1,1,1,1,1,1,1.

Daryl

David H.

Nosepicker,

This situation Mike explained is called "floating". When you have a circuit hooked up, and you are looking for a high signal, you want the pin to always read a low in a neutral state. That's why you would put a 10K ohm resistor from the pin to ground, like Daryl stated. Then the basic stamp will see a "0" all the time, until a high signal is applied to that pin. Then the resistor link is basically ignored by the basic stamp, and it will read the high signal.
Good luck with the projects.

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David


There are 10 types of people in this world,...
Those that understand binary numbers, and those that don't!!!

allanlane5

And yes, a "Floating" pin reads whatever RF is in the vicinity -- usually the 60Hz power mains frequency. So it WILL look like noise.

NosePicker

Wow it is amazing how much I have learned the past few days from this forum alone. I just wanted to put a shout out to thank all you guys for your help with my stupid little issues.

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Thanks

NosePicker