Building a basic volt meter

The "Eleven" is our Uno-equivalent Arduino-compatible board, but with a number of improvements including prototyping area, a mini-USB connector, LEDs mounted near the edge, and the D13 LED isolated using a FET. [Product page]
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lostinspace2011
Posts: 2
Joined: Mon Aug 17, 2015 4:28 am

Building a basic volt meter

Post by lostinspace2011 » Mon Aug 17, 2015 4:39 am

I am trying to build a simple volt meter using my eleven and a 16x2 LCD display.

This is what I have connected to far:
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With R1 being a 100K and R2 a 10K resistor.

This is where my questions start:

Should the connection from R2 towards GND go to the arduino's GND connector or somewhere else ?

Replacing the resisters with a 1M /100K pair should produce the same measurements. What are the benefits of using a larger resistor ? Ideally I would like to measure up to 50V safely.

The battery I am connecting this to produces up to 50V and up to 10A current. Is the suggested plan safe to use with this configuration ?

I would also like to measure the current flowing. I thought about measuring the voltage differential across a known resistor and work out the current from that. Again is this the best approach. What other options are there.

Brissieboy
Posts: 190
Joined: Fri Sep 20, 2013 7:25 am

Re: Building a basic volt meter

Post by Brissieboy » Mon Aug 17, 2015 11:40 pm

lostinspace2011,

The bottom of R2 (your negative probe) must connect to the Arduino ground.

The higher value resistor pair will provide less loading on the circuit under test (always a good thing), but it will also make the input resistance of the Arduino have more effect. Even though this is very high, it will have an impact. In either case the basic concept is OK. You will have about 4.55 volts on A0 with 50V input.

You will need to be very careful when measuring anything with a setup like this because of the ground connection to the negative probe. Also be a little careful with the voltage limit.

Current measurement is usually done as you suggest - measure the voltage across a series resistor. The resistor needs to be as low as possible to reduce the impact on the circuit under test. It would be best to use some amplification to increase the small voltage produced to somewhere within the Arduino's input range, but less than 5V for your maximum current. Another option might a hall-effect device.

BTW you can get a wide range of meters off fleabay for MUCH less than the cost of an Arduino Uno plus display.

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