# How a Multimeter Reads Current and Make on Arduno

First, I have tested ac current using a hall effect sensor (one specifically for small current loads) and the resolution and stability is not that great even when using smoothing code techniques. I'm just not satisfied with it. Also, I'm using the correct code to deal with the ac signal. I need to read between 0 and 80mA. However, my multimeter does a fantastic job with the readings!

1. What technology/system is used in a handheld multimeter to read current? I ask because when I use the multimeter, my readings are VERY stable.

2. Can I use the same technology used in my multimeter on an Arduino? Again, I am reading up to 80mA, so I'd like to use the full (or close to) full resolution of my 1024 analog signal.

Thank you in advance!

p.s. I'm not interested in a debate of how or why my sensor doesn't work. No talk about amps, current ACS712 sensors or INA 169...blah blah. I'm done with it. I want to know specifically how my multimeter works and if I can reproduce this on my board. Thanks you!

p.s. I'm not interested in a debate of how or why my sensor doesn't work. No talk about amps, current ACS712 sensors or INA 169...blah blah. I'm done with it.

OK, but your Arduino will give you stable readings if you feed it a stable DC voltage (and if the Arduino's power supply is stable and quiet).

I assume you know what AC is... It's constantly changing... If you just read the data it's going to look random (within a constrained range) and the Arduino can't directly read the negative half of the AC cycle. You'll need to calculate the RMS, or average the absolute values, or find the peak in each cycle, etc.

Assuming it's a 50 or 60Hz power line, you know you've got a sine wave. So, the easiest thing is to find the peak in a fast-loop every 20 milliseconds or so. From there you can easily calculate the RMS (since the peak-to-average and peak-to-RMS ratios are known for a sine wave).

1. Can I use the same technology used in my multimeter on an Arduino? Again, I am reading up to 80mA, so I'd like to use the full (or close to) full resolution of my 1024 analog signal.

Depending on the voltage you're getting out of your sensor you might need a preamplifer or you might need to lower the ADC reference voltage. (i.e. The optional 1.1V reference will read 1023 at 1.1V.) But if you change your reference and you've biased the input for AC, don't forget to change your bias to half the reference.

Also, I'm using the correct code to deal with the ac signal.

Really? Post it, using code tags.