sorry for my questions I am new in arduino filed and I have got some unusual problems to ...
my problem simply .. I need to flow some current in soil test filed in prob1 and measure it in the prob2
every thing works just fine when using UNI-T voltmeter ..
I have made a 5 v current flow in small soil test Filed and get about 4.45 v reading on the prob2
using Unit-T METER.
my problem when trying to measure that current with arduino it get less than 0.5 v reading ..
but the arduino reads the v very good when measure it directly without crossing the soil ...
it reads 5 v direct on serial print .. but when I make the current flow in the soil and get prob 2 reading get about 0.25 v
I am getting crazy because the UNI-T voltmeter reads the volt very fine after crossing the soil ...
because the soil is just as a usual resistance film ....
and arduino read it right only if it not crossing the soil .. talking about regular battery voltage measurement ...
when I use the voltmeter to figure out where is the problem I have found that :
the volt comes from prob 2 about 4.45 until make an attachment to the arduino analog port with 10 k resistance to the GND it directly goes down to 0.25
Your diagram shows the voltmeter in series with your circuit. You take voltage measurements in parallel.
I'm not clear what you are trying to do here. If you measure voltage then you would do so with a lead attached to each probe, and just read 5v.
The resistivity of the soil may have some effect, depending on how high it is, due to the soil resistance and voltmeter resistance being in parallel. Good soil woild have a resistivity of below 50 ohm meters. Bad soil coild be several thousand ohm meters.
Can you clearly explain what you are actually trying to do, and why.
You also need to be aware that you could have other ground currents present, such as supply fractional neutral return currents in a PME system, that will show a step voltage between any probes inserted in the soil. This could be non-existent to quite signicant, again, depending on the soil resistivity, test postion and magnitude of those currents.
If you put a voltmeter in series with your probes and a battery, what the meter reads depends entirely on its internal resistance. You are actually intending to measure a very small current rather than voltage.
Clearly your voltmeter has a much higher internal resistance than the Arduino analog input. An input in digital mode has an extremely high input resistance (tens or hundreds of megohms), but in analog mode it actually draws a small current on each measurement cycle, so has a considerably lower effective internal resistance.
Hi, what are you trying to do? And for what purpose?
I calibrate and repair earth resistance measuring devices and it can get very complex.
Pass a current through the earth?
2)Measure that Current? (Not the voltage.)
You need to have your meter in CURRENT Mode not Voltage.
For the arduino to do it you will need to provide a resistor in the place of your meter and measure the voltage across it, the arduino cannot measure current directly.
Dr_Pedantic:
A unity gain op-amp with very high input impedance should solve your problem.
I think not.
How would it solve the problem he has of totally not understanding what he is doing?
It would just give some other arbitrary reading with little relationship to what is trying to me measured.
