My Simple Arduino Based Multimeter

@valerio, good job!   After looking at your project, I have a few suggestions to aid you in further expanding it's capabilities.

The first thing is that you can improve of your accuracy by using a voltage reference module like the LM4040.

This will increase your sensitivity by making the reference voltage that the UNO uses ( by default 5V) for the ADC. As you can see from this equation, 5V divided by the maximum ADC count( 5v/ 1024= 0.004882812.

That means that .00488 mV is the lowest voltage that one count can read. A LM 4040 voltage reference module has a 4.096 volt reference.This mean that the resolution now is 4.096/1024 = 0.004 mV, or 18% resolution improvement, or sensitivity. 

The second this is, you can expand your measurement range to measure up to about a meg ohm..

The ADG609 is 4:1  analog multiplexer, I'm only using 1/2 of it, but it selects which range resistor is used with the Rx ( unknown) resistor as it forms a voltage divider network, so that the code and calculate the unknown resistance. As this is a word document, you can increase the zoom feature to blow up the drawing bigger so as to see the details of the connection better..the rest is self explanatory,  but should you have any questions or comments, please feel free to do so..

The following attached drawings , fritzing & code will help you see how this is accomplished.

Good luck with your on-going project.

kind regards,

LouisR

@inst-tech Many thanks for your suggestions and appreciation.

A small side note: the project is not ongoing. It can definitely be  improved, but I would prefer to restart from scratch.

If I did that in the future, I would definitely use a multiplexer for swapping between different resistors, as you suggested.

But would it work on voltage too? The measured voltage goes to the arduino through another voltage divider

so swapping between many dividers could change the maximum and minimum voltage that can be detected.

The current version of the divider is 5:1, this is one reason why the divider is so inaccurate with small voltages (25/1023=0,0244).

After an accuracy increase of five times, I don't think the LM4040 would be useful.

Also I don't think I would use a keyboard to control, I think I would use a rotary encoder (es. KY-040) with a knob, so that wiring is simplified.

Having said that, thanks again for your feedback

Have a nice afternoon