# Getting a voltage when nothing's connected

Just got an arduino, trying to learn the basics. So when doing the example in the link, I keep getting a voltage of around 1.5ish no matter what, even when the wires are not connected. Am I doing something wrong? It gets annoying when I try to make a program that uses input.

By the way, I'm not using the potentiometer, just two wires (with a resistor) one from 5v and one to A0.

No this is perfectly natural and will occur every time. Read:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html

Am I doing something wrong?

Yes. You will not see sketches for teaching fundamentals make reference to using a Digital Multimeter to read pin voltages to indicate logic levels.. You see LEDs used (or relays or motors or...). When you go off-script, things will not make sense. As your knowledge and experience grows, you will be more comfortable with the electrical operations of the circuit.

Ray

mrburnette:
You will not see sketches for teaching fundamentals make reference to using a Digital Multimeter to read pin voltages to indicate logic levels..

I actually took the OP's post to mean s/he was getting an analogRead which corresponded to 1.5v, say about 300 (ie 1023 x 1.5 / 5). Didn't seem to me there was a volt meter involved......

Didn't seem to me there was a volt meter involved......

Would not be the first time I got something wrong! I was suspecting a VOM/DVM measurement on the input pin and the associated digital reading did not match the expected. Your summation, however, sounds more likely - today

Ray

mrburnette:

Didn't seem to me there was a volt meter involved......

Would not be the first time I got something wrong! I was suspecting a VOM/DVM measurement on the input pin and the associated digital reading did not match the expected. Your summation, however, sounds more likely - today

Ray

One negative thing I've come to realize concerning digital DMMs is that they always seems to display some number even if the value is total nonsense because of the way the user sets the function knob, leads inserted to proper jack, and actual two measurement points being used by the user. An example might be a user attempting to read resistance on a circuit that is powered up. In the old day with analog multimeter you had better had a good handle on what voltage or current setting you were expecting before selecting and the nature of the measurement you are attempting to make, otherwise the multimeter soon became a ex-multimeter. And a Simpson 260 was a sad thing to lose.

Today many newcomers to electronics will assume the DMM is god like and whatever value being displayed must be correct. The DMM do a good job of self protection so there are few painful lessons presented to new users.

Today many newcomers to electronics will assume the DMM is god like and whatever value being displayed must be correct. The DMM do a good job of self protection so there are few painful lessons presented to new users.

Grew up building my own stuff: Knight Kit VOM, EICO grid-dip meter, etc. Puffs of smoke resistors on tube plate and the stink of selium rectifiers are etched deep in my memories. Shortwave regenerative receivers were foundational evolution after a few fox-hole crystal sets using germanium.

It is a great time to be alive; the toys are fantastic and relatively inexpensive. However, the historical path and associated accmulative knowledge is simply lost to the new generation that goes straight to digital and coding. Eventually, they discover analog and learn about induced voltages and ground loops. Still, the stink of selium will likely evade them forever! XD

Ray

Still, the stink of selium will likely evade them forever!

I can't say that will be a great loss.
Only smelled it once myself when I was about 16 and was told I would never forget it. That is very true.

I think he maybe meant selenium. Never heard of selium. Smoked selenium smells a lot like rotten eggs. If you've never smelled rotten eggs, you haven't missed anything.

Selenium, interestingly, is potentially toxic, but also an important trace element in our diet, the lack of which is held responsible for various or many health problems. In very small amounts.

As are of course, various other elements.

Selenium is what the legend......wait for it.....ary Chester Carlson used in the first Xerox copier, and it stayed as the coating on their drums and belts for decades.

Interesting Xerox factoid.... one early model, I forget the number, had a habit of catching fire. Engineering's solution was to ship a fire extinguisher with each machine. Marketing got their knickers in a knot over that, and said "Guys, you can'r ship a fire extinguisher with a machine. The public will think the machine is dangerous. We'll call it a Scorch Inhibitor instead." And it came to pass.

I think he maybe meant selenium.

I did. Either my fingers can not spell (usually due to lack of coffee) or I was a victim of the spell-checker... I cannot say.

Ray

I had a colleague who was once working with sulphur, selenium and tellurium at the same time.
The smells she could produce were among the worst I've ever experienced!

For the moment some of the guys are using dimethyl sulphide. Just trace amounts of that stuff, will make half the building smell like rotten cabbage.