IotaWatt 4.0

Working on both.

Could you tell me what kind of tvs you used? The schematic on github didn’t specify the type.
I am also a bit confused: there is 1 vt connector (next to the nodeMCU) but the firmware lets you specify the inputs as CT or VT. Can one just connect a VT to one of the stereojacks (so i can connect 3 VT, one for each phase of my 3phase system?)
(sorry for my noob questions)

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You will need to remove the burden resistors on the two additional voltage channels, and present the AC reference signal using an attenuation circuit consisting of a 10uf capacitor in series with a 12K resistor and a 1K resistor. Input the voltage across the 1K resistor to the IotaWatt channel.

If you stare at it for awhile, you will see that replicates what is in the dedicated voltage input.

There are other ways to do it as well:

Replace the burden resistor with a 1K (0805) resistor and connect the VT leads with a 10uf capacitor and 12K resistor in series.

Lastly, don’t remove the burden resistor and connect the VT leads with a 10uf capacitor and a 288ohm resistor (or some close standard value like 270 or 330). This method will draw about 40ma and dissipate about 40mw of heat from the burden resistor, but if you just want to experiment it should work OK.

You will need to calibrate those VT channels as described in the GitHub WiKi.

Thanks for the clarification, i’ll change 2 inputs to look like the dedicated voltage input.

Is this type critical? My online shop (conrad) isn’t carrying them, and mouser/rs is charing quite a shipping cost. I suppose it has to be a 3.3V vrwm, but any other specifics needed?

I get them from digikey. Their shipping via usps (USA) is very reasonable. Probably around $3 for just say 10 of these and 3 days. That said, you can actually leave them off entirely and the thing will still work, just no additional ESD protection beyond the nominal provided in the ADCs. Using these arrays instead of simple TVS diodes provides some “rail to rail” protection against overvoltage from the VTs and CTs.

Other manufacturers make sot-23-6 diode arrays that should substitute just fine. I just looked up ON semiconductor CM 1224 which looks fine in the 3.3v version.

Thinking about this after I responded to your last inquiry, I have not actually tried any of this, although I have high confidence it will work. I’ll give it a shot over the next few days. The idea of leaving the 24 ohm burdens in place and using an external 300ohm voltage divider resistor seems better to me now that I’ve thought about it. From the perspective of power dissipated through the 24 ohm resistor, it’s the same whether you are using it with a CT or a VT in this configuration.

The capacitor is really not necessary either in the normal case, I’ve just always used one there. Initially I put one in because it’s common to find D.C. Wall supplies that have the same 5.5mm plug, and I wanted to protect against accidental use of one. That’s probably not a catastrophic problem anyway as the D.C. (iOS wants the periods) would need to be more than 12 volts to overvoltage the ADC.

So it looks like it should work ok plugging the VT right into the 24 ohm burdened channel using about a 300 ohm resistor in series. Simple enough. I’ll try that out over the next few days and get back.

@promy

That was easy. I soldered a 3.5mm jack on a VT with a 330 ohm resistor in series:

Plugged it into an IotaWatt input and configured it as a VT. Calibrated it as per the WiKi instructions, and ran it for awhile. Here is a graph of the standard VT input and this additional VT on channel 1:


So that’s all there is to connecting and configuring another VT. Once an additional VT is configured, there will be a selection box listing all of the VTs when configuring a CT.

Looks great! Perfectly aligned!
In a few weeks i’ll give it a try, I ordered the components and the board (slightly adapted to minimize the number of smd since i do not have much experience soldering them) from dirtypcb.
I will try it first without the tvs (they charge 20€ shipping to Belgium…)
Maybe i should have waited till your response, but i changed the input 1 and 2 (adc 11 and 12) to the schematic for the VT.
Looking forward to “playing” with it :wink:

Maybe a stupid question, but how do the inputs on the webpage relate to the adc’s? 0 is the dedicated VT (thats ADC10), so i was unsure if the nrs on the pcb are the nrs on the webpage.

Sounds like you have everything under control.

Its not a stupid question, but it is something that you should come up to speed on if you intend to build and troubleshoot a unique implementation of IotaWatt. I think you will find that taking the time to understand the overall structure of the program will save you a lot of time down the road.

With regard to this particular question, the latest schematic on github has the inputs labeled J1 - J14 and they have corresponding ADC input nets. The firmware currently on Github configures the inputs that way in the default case, but any override mapping can be specified in the json config file.

Happy prototyping.

When i get back from holyday i’ll get up to speed on the firmware! (been looking a bit into it but luggage duty for my wife is more important :wink: )
On your reply: in the schematic (4.1) the J1 to J7 is connected to ADC11-ADC17 and J8 to J14 is connected to ADC1-ADC7 (thats why i was a bit confused), but when looking into getconfig i saw that you switched the mcp3208’s

When looking through te code i was wondering: greenLed is defined as 0 , isn’t this giving any problems with the ADC on the same pin? (or is it multicolor led?)

That’s probably a good idea. Using the 24 ohm burden and a 330 ohm voltage divider the 24 ohm burden dissipates about 27mw of power, which is fine for that SMD resistor on the open board, but the 330 ohm voltage divider gets the lions share of it and dissipates about 380mw. In that closed connector, it heats it up enough to feel it:

You can make out the 3.5mm jack - that’s the one that’s marked 100F. You can also the nodeMCU. The cool square (blueish) is the actual shielded ESP8266. The bright spot to the right is the voltage regulator. That gets a bit warm as well.

So for a permanent install, I’d recommending getting larger resistors for the voltage divide, even if it means replacing or removing the internal burden resistor.

Fantastic nice work @overeasy!

For some time we have been in communication with @overeasy regarding ongoing development and stocking the IotaWatt in the OpenEnergyMonitor shop. We should have an initial ‘dev’ quantity of units in the shop in the next month or so.

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Awesome, can you give us hint on the pricing?

I’m afraid not yet. Final manufacturing details have yet to be finalised. Too early for pricing, I would be making up figures if I tried to give you an indication at this point. Very sorry.

Pricing may change between this first pre-production run (50-100 PCS) and the final production units.

I’ll let you know pricing as soon as I can.

I really like what you are doing. So smart to embed a Feather w/ WiFi. Is it possible to share the schematic and BoM? I’m interested in morphing it to have 20 CTs and use a Feather M0 RFM69 instead of the ESP826 (then RFM69 to a “base station”).

Well done.

Checkout the hardware folder of the IotaWatt Github repo for a schematic:

Look for iotawatt on GitHub. There is a schematic there for the latest version 4 iotawatt that supports 2 ADCs and 15 channels. That should be enough for you to go on if you are contemplating using a different processor. The ADC circuitry scales pretty easily. At the end of the day the hardware is just an ADC shield that connects to your processor SPI.

I abandoned the feather design some time ago in favor of the current design that is simpler, less costly, and fits in a nice enclosure. The ESP8266 nodeMCU is a commodity board that sells for less than $5 free shipping. Shipping alone for a feather is more than twice that, so I gave up on that approach. Except for the battery charger, there is no functional difference between the feather ESP and a nodeMCU.

My pcb from dirtypcb arrived yesterday. However, I seem to have made an error ordering the caps (i ordered 10nF in stead of 10uF…) . So i was wondering if C9 (10uF cap just after the power adapter) can be a polarised Electrolytic capacitor? And if so, how should it be orientated?
The same question for the C1 (10uF, next to the lm358). This one is connected to gnd, so orientation is obvious here…

Not sure which schematic you have. The most recent has four 10uf caps. Three of them go to ground and handle D.C. So I would guess electrolytic would work. There is a capacitor in series with the AC reference voltage divider that is handling AC so that can’t be an electrolytic. You can just remove the capacitor and short the connection. It is only there as a D.C. Filter to guard against against someone accidentally plugging in a DC source.

If you don’t have the most recent schematic, take note of the RC circuit on the Vcc pin of the Real Time Clock. This is needed to fix a problem with intermittent failure to switch to battery backup.

I am using the 4.1 schematic (modified) dated july 6th. (from github, seems to be the lastest?)

there i am seeing 2 caps marked 10uF (C9 and C1). The others are marked .1uF (C3, C4, C5, C6, C7)

I just posted the 4.3 schematic.

4.2 adds using the spare lm358 op-amp to bias the channel 0 AC reference voltage.

4.3 fixes a problem with the RTC battery backup not always working.