Hi,
I was wondering about having a Varying voltages from negative to positive.. I was wondering if I can do this kind of circuit?
if not do you have any ideas how to measure positive and negative voltages that are varying?
I've read, in order to read negative values you can have a voltage divider. But my problem is that i have only one vi.. and if i put the positive values on a voltage divider, i may get 10V.
Your basic idea looks like it would work, with a couple of limitations...
What kind of source do you have? What's it's impedance or current capability?
Diodes are nonlinear. You need to have 0.5 - 0.7V across them before they turn-on. That means you are not going to read any positive voltages below around 0.5V, and you'll need to add the diode-voltage drop to any readings you get. (You can do the compensation is software.) The biasing resistors on the negative input will turn-on the "negative" diode, so you will be able to read small negative voltages, but again you'll have to compensate for the diode-voltage drop.
Also, you WILL need that voltage divider for +10V, because connecting more than 5V to an input pin can damage the Arduino.
thank you very much for the reply.
that's a good idea of the voltage drop of the diode. i almost forgot that..
I think i will handle the programming of this. I won't stop till it work..
Im worried of my setup that it won't work.
But because you said it would possibly work, I will try it later this day.
i am thinking of an input of a Function Generator that gives a sine wave that has maximum of + and - 3 volts peak.
I just want to show my instructor that arduino can also read negative voltages.
A question about the input impedance or current capability, is this very strict?
Do i need to put resistors to balance their impedance?
You might try just the "-" circuit shown without the diode, and apply your +/-3V
signal. Use R1 = R2 = 10 Kohms, see what happens.
The important thing about R-values here, and everywheres, is that your measurement
ckt should not load down the source voltage. So, you should have Z(source) much less
than Z( measurement circuit).
hi i got great news.. it works.. but ive not tested it yet to other voltages. i was surprise when i put -5v it was zero, and when i put +5 v it was 5v, now i just edited my processing and it works pretty well. i just need to try it on a function generator. maybe tomorrow. thank you once again.