The Arduino Energy Monitor

I’m interested in finding out just how much energy my TV/computer/coffee machine/whatever are using, but didn’t think the Kill-a-watt style monitors were particularly useful - they only show instantaneous power usage or a cumulative total since the device was plugged in.

So I built one that uses an Arduino to measure the voltage and current and then report the power used to a PC via an XBee shield. The PC then logs the result and also posts it onto the Internet at Pachube.

I’ve just got it all up and running properly, and there are more details at

If you want to see how much power is being used right now, have a look at

That's very cool! Will you share your code?

This is one of the projects on my list! (Although a slight variation.) Could you tell us what current sensor you're using?

tedder: Once I get the hardware fully sorted and release the designs, then I'll include the code too. The code isn't that useful without the hardware anyway.

DaveAK: Current sensing is done by measuring the voltage drop across a current sense (0.005 ohm) resistor that's wired into the mains. It gets isolated from the Arduino board (and amplified to the range of the Arduino's reference voltage) by an HCPL-7520 op-amp

I'm working on a montor for gas,water and electricity have the gas done. I'm using a IR reflective sensor, outputs rate and amount used.

Have you guys seen this page 8-) looks very interesting :)

The guy at is taking this stuff to a whole new level.

I hadn't seen Plugwise before, they look like they're doing something very similar to me.

I'd be interested to hear more about how you're monitoring the gas. Are you measuring it at the meter? I had an initial look at my gas meter, but it's a new digital type and seems to use some sort of ultrasonic sensor for readouts - I haven't wanted to stump up the ~£150 for a copy of the standard used yet ;-)

I have come across a couple of other people doing gas measurement recently - there's a guy who's using a cameraphone to notice when his boiler kicks into action and someone else who's stuck a reed switch onto the side of his old-style gas meter and measures usage with that

Hi Adrian,

Thought I'd reply to the group - also got your email thanks. My Gas meter in the old type with 'analogue' digit numbers the last '0' (.001 M3) has a mirrored centre and using a reflective IR sensor I count the digit as it passes. It seems to work very well as long as the sensor doesn't move - got it stuck with brown packing tape :). the Arduino displays use in watts and rate of use in watts, also outputs the same on the serial port. It's all very alpha at the moment just proof of concept. We have a new electronic electric meter - the type with the flashing led 'once per watt' so just need a photo transistor blue tacked to it. Water, we have a meter with no real way of reading it nothing reflective rotating needles and numbers if you know the type - one thing I have noticed it goes clunk every 10 litres so maybe a piezo sensor to detect the 'click'.......?

Okay. I'd heard rumours of that approach to the gas stuff - nice to know that someone has actually done it. Look forward to seeing the finished version appearing in this forum sometime ;-)

I haven't looked into water meters much, because we don't have one here. I did come across some info whilst I was looking for info on the gas meters though, and it could be that the clunk is the "pulse" referred to on Maybe there's an electro-magnetic pulse to accompany the clunk, and that might (or might not...) be easier to detect than listening for the click?

Thanks for the info.

My plan is to measure the energy per circuit by using hall effect sensors at the breaker box. There are a few options available which is why I wondered how you had yours set up.

I hadn't thought about gas measurement, I'll have to take a look at our meter and see how it's set up. As for water, we have our own well, so the cost is the electricity used to pump it out of the ground. It would have been really handy to have been monitoring things more closely though when we lost pressure and didn't realize that the pump was running continuously! That cost us more than a bob or two in wasted electricity. :(

Yeah, my solution needs to be wired into the circuit which isn't really an option at the breaker box :-)

Once I've got the individual monitor/controller working fully, I do want to add something to monitor the energy per circuit at the breaker box too. Then I can get overall energy usage for lights and everything else, and put individual monitors on things I want to measure specifically or control.

I'd love to hear about it when you get it up and running (and if I get to it first I'll report back with what I've used)

Have you see It also has an open API which is pretty simple to use....

Cheers, Crispin

Interesting thread. I'm keeping this link for further investigation -

I was thinking on using a hall effect monitor and a coil around the cable to get how much current is used by these device at any moment.

Could this be plausible?

I am currently building something similar for a class in school. Going to monitor power to 6 outlets and and be able to turn them on and off using a remote control to turn off leech currents. Ideal placement would probably be in a home theater where you already use a remote to turn your stuff on and off.

Anyway, a hall effect could work, but you would need to calibrate it, or you can use a current transducer, which should already be calibrated.


Jim, I was just thinking about something like that last night. My TV is one of those kinds that has a fan in it which runs all the time, even with the power off. So I was envisioning what you described with both a current sensor and a remote control feature that delays its own shutoff so that a projector type TV can cool down before losing power.

I was also considering building this into a battery backup unit so that you could COMPLETELY disconnect power from the mains and run the control circuits from the battery when everything is turned off.

I'd love (hate) to know how much electricity my entertainment system uses. Then I could charge my kids for playing video games so much! ;)

Thats nice, Pachube looks like a great Place :)