This is where we will track our progress in completing the design for the EnerJar.


  • Auto-ranging: waiting on digital potentiometer from Microchip
  • Create more detailed parts list with proven/suggested suppliers.
  • Test a cheaper/smaller microcontroller 16f887 perhaps: waiting on samples from Microchip
  • Get a PCB layout designed and ordered
  • Measure the EnerJar's readings against a reliable reference meter to prove our design
  • Calculate long term totals
  • Calculate more geeky figures like frequency, voltage, current and power factor
  • Check allowable ranges of values for components (caps, pot, resistors)
  • Create a debug mode for debugging the circuit if something isn't working
  • See if we can use Vref+ and Vref- only for current reading, and use full 0-5v for voltage

fixes in version 0.8.1

  • Calibration system- 2 buttons: one to set zero-level and one to set a known power (like a lightbulb)
  • Are incandescent lightbulbs even consistent enough for this to work? Any other ideas for a device that consistently uses the same amount of power?
  • Make sure that the code would not need to be changed for a 240-volt version
    note: the calibration range is large, so 240-volt should require no change in software


If your looking for continuation of a project like this Ive started one here: the design is open source and builds upon the PowerBox guys design with an Arduino and Java software.

interesting question.. well, i hope it is..

how will i make this enerjar project something that adds up the total power usage instead of just having the instantaneous reading only.. please help me..

I am trying t realise this

I am trying t realise this project.
Matt can you help me with getting the components?

Dumbasses - There are people interested- dont wait too long

Guys, I know that you are busy. -BUT- You started this project, now finish it. There are real live people interested in what you are doing, but every day you wait, you loose them as supporters and intern loose their resources.

Dont burn bridges here - you had a very good idea, and you did well with it. Keep on Trucking!

Hi! Im just wondering what


Im just wondering what is happening with this project. It sounds really interesting and Im about to soon build a couple of this and wonder if there is any updated information? How tested is this? Is it confirmed that it works good on 220 v? Dont want to fry up the school ;-)

Anticipation ...

Guys: I'm trying not to be anxious about this project, but sure would like to get an update on where you are and when you think you will have finished hw & firmware. Best of luck.

Re: Anticipation

Thanks for your enthusiasm in the EnerJar! We are really sorry that we haven't been more prompt with our promised update. With schoolwork and all our other commitments, we haven't spent as much time on the EnerJar as we should be. I hate to be fuzzy, but we're planning on working on it this week, so hopefully we'll have something to show for it soon.


Re: Anticipation


Thanks for the update. My concern stemmed in part from just not having seen a post from either of you two in weeks. Now that I see you're at least looking at the site (and perhaps having guilt trips), I'm happy.


Mailing list

Please put me on your mailing list

Watch out

If you are giving these away, you may want to add reverse polarity protection and esd protection (among other things) to make sure that people you give them to don't immediately fry the boards if they connect the power supply incorrectly or decide that they wanted to rub their feet on the floor and touch an i/o pin on the PIC.

Cheaper Processors

If you are looking for a less expensive processor, that will also give you more power, look at an AVR. You could probably fit this into an 8k to 16k flash AVR (or AVtiny) device easily and then all the tools (compiler and programmer) are freely available on the web (see WinAVR)

Current Draw

Sure LEDs are relatively cheap and easily understood, but for regards to current, wouldn't it be better to use a simple LCD (2x16 parallel LCD would probably be more than sufficient) and it would take much less current!

Along the lines of PC communications, there are a number of USB to UART type devices (see Cypress, FTDI, or even some PICs and AVRs have example designs of the sort) that you could probably easily integrate and then the device could be USB capable - meaning you could communicate and log data with a PC and even power it from your PC (rather than the cell phone charger)

RE: Computer Readout.

Hi there. Firstly this is a great simple design.

I am currently in the middle of building my own Home Automation setup and was needing something to measure the usage of power points and lights. This design will allow me to build the unit directly in the wall itself attached to the rear of each point.

What I was interested in thou is if there was anyway to cheaply and easily enable a computer readout to be monitored by home automation software. This should allow me to read weather a light has blown or even if the fridge is still on and running. Also it will allow me to calculate the total power use of the home and have it automatically adjust equipment in terms of Solar Panel setups etc.

Preferablly I would like to have ethernet connectivity if at all possible. Maybe there is a Server in a chip solution we can add that will output a XML file every so many seconds for the computer to read. Being ethernet firstly allows for longer runs and also may allow the ability to connect using Ethernet Over Power.

Please let me know if anyone knows any solutions to my questions.

RE: Computer Readout (solution?)

Shaun; I just found out about these, so I've never used them, but they seem to have the capabilities you were looking for. Easily interfaced with microcontrollers, and have a built-in webserver. or

RE: Computer Readout.

Thanks heaps for the links. I have seen them before but I never actually read thru there other products.

The 2 you mention would do the job to a degree but the XPORT AR is the missing link I actually need. It supports CGI, AJAX, XML and RSS.

This means that I can take a reading from a serial device, and output that data along with Identification information and even say a measurement time and date as an XML or RSS file. And then as we all know I can read and manipulate other gear on the system.

Thanks again for those links.


Calculate more geeky figures like frequency, voltage, current and power factor

Power-factor isn't so much "geeky" as "necessary" to provide useful measurements for anything that isn't a simple resistive load (i.e. nearly everything aside from light-bulbs and electric radiators).

Re: Geeky?

The EnerJar is correctly measuring the real power. Power-factor, real and apparent power were all taken into account when designing the circuit, however the power-factor ratio is not currently being displayed.


I am just getting into Embedded Design. Microchip has an example of a utility power monitering system. Cool Project. Can't wait to build one, I have always wanted a watt hour meter of my own. I hope it will work on 12vdc as well so people can understand how much energy, and thereby gas they are using to run things in their car.

Dummy Load Choices....Be Careful !

Enjoyed having read about your device in local newspaper, and wish you best of luck w your endeavors. Looks as tho you are likely EE majors or some subject similar to EE career minded inventors including Computer Science types. As an old retired EE mfg and reliability eng, I would advise against any power transistors and associated heat sinks, power resistors, light bulbs, etc., on the inside of your isolation case (glass insolated jar) that is housing your logic devices. They'll need their own well vented isolation case. The heat output from those devices captured inside a jar will affect the ICs accuracy if not outright kill your ICs if the users have them plugged in for more than a few minutes. Also, if you move any heat generating components to another case, the 5 V battery being used as a ref source can be replaced w a simple series pass voltage regulator. The battery is fine as long as it is fully charged but what happens to the validity of the op-amps outputs when the battery output falls below 5 V.

Consistent Power Source

A great thing to use is a bench top power supply used by many hobbyists. One that varies its amperage would be ideal


Great project! I can't wait to build one... For calibration, I'd try making a dummy load out of a big power resistor across a plug. I'd think that would be way more accurate a user's lightbulb (of unknown brand, age, wattage, etc) and should only cost a couple of bucks.

Oh, another thing... since

Oh, another thing... since big cheap power resistors don't tend to be high precision, some way of entering the true measured resistance of the dummy load would be great!