I wish to build a datalogger for a geophysics project.
The logger would be used to store and measure potential difference ranging between +/- 1 mV to +/- 2.5 V DC, with a resolution of <1 mV. (1 amp max).
I have built temperature loggers before, so most of the build I can understand. Capturing the Voltage (range and step value) is tripping me up right now.
My question is this:
Rather than reinvent the voltmeter, can I take off the reading from the LCD of a multimeter so I can parse the data with software to the logged string on the Auduino?
Only if your multimeter has a databus.
There are simpler ways, using Arduino's analog ports to measure voltage but the 1A is a concern. You would need to limit this to make sure the Arduino does not fry. It can sink max 40mA, so 1A is much too high.
Found a couple of usb multimeter options will pick one and start building. One academic paper on linking a DMM to a RasPI.
Check the driver requirements.... Usually, the USB driver will work with Windows and possibly OS-X, Linux (for the Raspberry Pi) is less common, and the Arduino doesn't have an operating system so your odds are worse with the Arduino.
If you can find a meter with an RS-232 interface, that would probably be the easiest to adapt (because RS-232 doesn't require a software driver). But, RS-232 instrument interfaces are not common. The most common instrumentation interfaces are USB, GPIB, and LXI/Ethernet.
You can us an ADS1115 it has a programmable gain amplifier PGA and has 16 bit of resolution. It has 4 channels that can be used as 4 separate analogs of 2 separate differential analog inputs. Setting the gain to X1 will give you a resolution of .125 mv with a range of +/- 4.096 volts. Setting the gain to 2/3 will give you a range of +/- 6.144 volts and a resolution of .188 mv. I connects via I2C. I have them cheap on my web site. They are easy to use and a library is available.
I use them in a lot of modules I have designed and the most I have run off of one Nano is 12 using an I2C bus switch giving me 48 channels total using my Base-Master.
With an ADS1115 and an amplifier to shift the voltage into unipolar, you should be able to do the measurements. I don't know about 1 amp rating. It makes no sense to me without more information. Are you measuring the output of a sensor or else?
What I'm trying to build is a logger which records voltage and GPS. This will be used to test a geosynthetic liner( see information below.)
The idea I have is to build a data logger which geo references each voltage data set. So that I can output to a 3D drawing package such as autocad. X,Y,voltage (z).
Present equipment only references the voltage and we have to estimate the location of the data point. The old school Cambridge loggers need to be kept in a backpack and only work with a laptop running XP.
I'm progressing the RS 232 ideas, once China Post lands the DMM I can start the build and feedback.
Thanks for all the comments I know it can be done, the rest is a few late nights staring at code.
As far as I can tell, there is no flow of current across the electrodes with the voltmeter. You must have confused with the driving current. That could be an amp. Which campbell sensor does your old logger use? Give me a link.
