Need a module designed - Gadgeteer - Kill-A-Watt + PowerSwitch Tail

Hi everyone,

I have an idea for a standalone monitoring system and need someone with a bit more electronics knowledge to design (and produce at first) these modules for me. I can provide financing for parts and the circuit board runs and pay for the assembly. If I get enough demand for the assembled monitors, I would likely pay to have a pick and place template put together so they don’t need to be assembled by hand.

I want something with a Gadgeteer interface with the following functions:

Must Haves
Monitor current usage up to 5A (10A or 15A would be a bonus if it doesn’t increase the cost significantly) through a standard US 3 prong 115 plug.
Report volts, amps and wattage within .5% accuracy
Pass current through to consuming device
Provide power to a gadgeteer mainboard from same plug[/ol]

Nice to haves
Allow gadgeteer device to turn on/off consuming device (gadgeteer device would stay powered via main plug tap)
Ability to change to international plugs [/ol]

[1] PowerTail Switch II -
[2] KillAWatt -

Feel free to post interest/conversation here or email me at Steve at DevOnBoard dot com with a proposal

BTW, I do plan on this being open hardware. I’m paying for the design and your manufacturing time, so this would go to the community once I get the finished product.

I think that would be a huge selling module as I know I’d want some. I hope someone jumps onboard with it @ stevepresley

While the design work would be highly interesting, I certainly wouldn’t be willing to sell anything that others might plug into mains power. If a structure burned down, I wouldn’t want anyone coming after me…

Any idea how much would certifications like CE or UL or similar cost?

I would be happy to help with this module steve.

As a electrical engineer this is a pretty easy module for me to mock up, give me a few days and I`ll get a design together. [currently working 4MW motor inverters at work that’s 4 megawatts so a few amps of mains should be ok :)]

I wouldn’t want anyone’s place to burn down either.

I’m hoping whomever I can get to help design it can source the power components that are already UL certified or the cost of such isn’t prohibitive.

Awesome! Feel free to shoot me an email if you have any questions about the design or my (first) intended use for specifics.

@ stevepresley - Ill pull something together over the weekend then we can see if Im heading in the direction you want.

1 Like

@ stevepresley -

ok I have started to look at what would be required, heres what Im think so far.

AC Power Measurement

active power
real power
apparent power
line rms voltage
line rms current
line frequency
power factor

all of the above pretty easy to read. would need a current transformer for dropping the current to a useable level and a voltage divider/ rc filter to process the voltage. both of these measurements can the be processed via a energy monitoring IC and the data could then be made available over SPI to the main board. I wondering whether a onboard CT is best or terminals for a user to connect there choice of CT, I think I prefer terminals as the current measurement is only limited to the size of the CT [and ratio] here board mounted would fix the max current . I have a prelimary schematic for this part strew across my desk, will try to get it eagled up in the next few days, as work is killing my time at the moment.

DC Supply
powering a gadgeteer board from this module makes life interesting, as the board become a black and red board at the same time lol. looking at the client dp module design, that part of the module seems doable, no need to reinvent anything within this area. wondering if you want to keep a usb prot for programming on the module like other power modules, I`m guessing so.

This leave a couple of things to consider, would this gadgeteer board be red or black ??

do you want a transformer with full rectifier etc etc to drop the ac down to say 12-30vdc for chunking into the switching regulator for the 3.3 and 5 vdc supplies? or maybe go with a capacitve / resistive setup i.e. transformless ac-dc conversion. ?

maybe wondering about monitoring the 5v and 3.3 dvc voltages and currents as well.

after some consideration there is almost two modules contemplated here a new client dp module ac fed and dc output monitored, a separate ac energy monitor module or a combination of both ??

what are your thoughts?
i`m out on work site visits for a coupl of days so i probably wont see this until Friday…


probably you never heard of Plugwise. They have more or less what you want, but as added bonus, they transmit all the values with zigbee (using mesh technology) to a base station. I think it would be worth looking into this, although their site is not available in english anymore:


Great work - comments below

Sounds good!

Hmm… I hadn’t thought about the board color.

If we do it as one board, since it deals with powering the mainboard, I would think it should be a red board. And yes, a USB debug port would be required.

We could have a power output that would connect to the 5v barrel jack on a red client DP module and not have to engineer that portion, although I suppose wiring it to down convert the AC to 5v to the barrel jack would be roughly the same amount of work as just making it D socket compatible. We’d also have to incur the cost and solder of a barrel jack instead of an extra gadgeteer socket/pad.

Am definitely thinking this is a two or three socket solution - would be possible to do a black solder mask as the base and then do a red block around the D socket when the printing overlay gets put on top? Maybe that’s a better solution?

As for the power conversion/rectifier - almost talking greek to me :wink: Yes, we would need a 5v/3.3v kick down to power the mainboard, but whatever the circuit is rated for should be able to be passed through to the slave devices - think 3d printers, CNC mills/routers, network applicances and home automation (toasters, coffee makers), etc.

No, I hadn’t heard of them. I’ll check it out and see if it’s something I can use. Appreciate it!

@ Nubiarn - any progress?

This is a module on my watch for list so I’m hoping there is some good news about when this will be ready.

Me too…