RJ45s are a real pain to crimp - these look like a much better solution. No special tools, just a screwdriver.
Simon
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I agree, these are really nice, I’ve been wondering if it might make sense to replace the CT jacks with these connectors to enable shortening and extending of CT cables for a neater install…If we can get them for the right price would it be a better solution?
Oh yes, I was suggesting the expansion board so a pre made network cable, then the screw terminals. Just a thought.
I think that exp. board is quite expensive?
Interesting to think about pluggable terms blocks for the CTs…
Couple of point worth repeating about this design are the two RJ45s are for temperature OR pulse sensor inputs each, there’s also an ADC channel connected to one of the pins in each one, I can’t remember why. Something to do with this? EmonPi - OpenEnergyMonitor Wiki Why is the ADC channel connected on the emonPi?
Five 3-wire term blocks are on board, however one of them is in fact 2-wire MBUS. It remains as a 3Wire term block for BoM simplification and keeping cost down.
I need to make a diagram of this at some point.
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Jacks are also a pain if you want to shorten a lead. But I guess it depends on price.
Another solution would be to offer an interface board with jacks on shortish flying leads soldered onto the board and screw terminals on the other side to take shortened (or lengthened) leads from the CTs.
That way there is a simpler to implement solution for those wanting to make their leads the right length. The rest of us that don’t care about a few messy loops can just go with the pre-soldered jacks.
Simon
Don’t forget the market you’re aiming at. I’m not sure what it is, so something “idiot-proof” like a jack plug, or a c.t. that comes with the 3-pin plug fitted, might be necessary for some users, whereas some won’t be put off by screw terminals, and others are going to have a RJ45 crimp tool to hand.
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I think I agree.
A CT requires only a 2-wire also, so 3-wire could be space wasting or awkward. The 2-wire version exists, similar cost, not a problem.
I fail to imagine any major benefit to having an alternative to the 3.5mm jack. If a cable needs to be shortened, there are ways to do that outside of the unit, without us compromising on cost or design simplicity, the 3.5mm plug from a CT can be recycled in any cable-shortening efforts I’m sure.
I don’t know the YHDC parts in depth… they do come in a wide range of Amperages. There are other brands using 3.5mm jacks also.
I notice there are a few CTs available with flying leads only. Given the compromise that would be required by the majority in adapting the YHDC CTs to screw terminals, perhaps the more fiddly compromise is better received by the minority who’d like to use something custom, in which case soldering a 3.5mm plug onto the flying leads isn’t too big a deal. The flying-lead only exist for the 200A+ CTs, this implies specialist installs to me also.
Also, the quantity of CTs on this unit implies sub-circuit and 3-phase monitoring, and the 3.5mm plug editions of the CTs available go up to 100A…
Are we on the same page?
I’m not even going to suggest a polling tool on this one. Got to avoid this turning into a smorgasboard! 
… Check out this at Mouser. Boom.
BMP680 is what you were thinking of I suspect. I bought one but it didn’t really like the harsh environment of my MVHR unit. I’ve gone for an SHT20 instead (temp and Hum only).
What I would say, is the chances of having enough items that need monitoring close by to this unit are fairly remote so the number of ports you have might be overkill.
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When it is moulded on? Are you sure?
Yes. How about:
Cut the cable leaving some spare at the strain relief.
Shorten the cable.
Join both sides.
I’d recommend a wago connector if speed’s the game.
If there are strong feelings on this we can make, say, 3 out of 9 CTs available as the pluggable terms. However I feel strongly this will be the exception to the majority, so I’m reluctant at the moment.
I could have sworn a decision had already been made to make to front end interchangeable so that any configuration of connector styles of any quantity of any mix of AC, CT or Temp etc could be knocked up on a cheap sub-board. How many AC inputs will this have? ie can it be used for all single, split and three phase installs without wasting IO or “cobbling” together an adaptor to re-purpose CT inputs as AC inputs?
I see the 3.5mm CT connector as a catch 22, because we only have devices using 3.5mm plugs therefore the majority of users have to use 3.5mm plugs. Don’t get me wrong, I don’t mind the connector style, I just dislike being restricted to one style. Rather than plugable screw terms I would probably prefer to see screwless terminals so that bare wires can be passed through small holes and connected direct to the device.
Three terms per CT would be useful for positively proving whether a CT is connected or not.
Is there any issue with the Silicon Labs Si7021 already used in the emonTH v2? I thought that was the winner when Glyn researched all these devices?
If there was a 4pin 3.5mm jack available with I°C these sonoff sensors could be could be easily used to avoid self heating from the CPU and voltage regs etc.
Although I do like the 3 pin conns you have selected (I use them for modbus/rs485), I just think they should maybe be 4 pin, Vcc, Gnd, SDA and SCL. so that devices like the temp/humidity sensor are connected by one connector, not by separate power and I°C conns (especially if that could introduce a ground loop)
However if you follow sonoffs pinout and select the appropriate IO the same 3.5mm connector could be used for DS18b20 1-wire too
With regard to a sub-board front end, it doesn’t necessarily ned to have a connector, for example just a row of contact fingers at the edge of the board would allow for a run of the mill PCB edge connector or alittle bit of paste and some heat and the boards can be (semi-)permanently joined with little or no additional contact resistance. Even if this isn’t marketed as “interchangable” when OEM want to launch other variants, the main board can remain the same, just weld a couple of different sub-board to it and you have 2 or 3 different models to flog.
The breadth of connector possibilities brought forward in that one post illustrates exactly why the basic board design is ‘Good Enough’. Perfect doesn’t exist, as I keep encountering.
And this does have to be focussed on energy monitoring using CTs, it’s not a glorified stm32 breakout board. (or is it?!).
The I2C divided across two connectors is a secondary result of needing, more fundamentally, a 3-wire connector. But I2C is an interesting one to think about… It’s a recently done bit of routing… We could consider a dedicated 2-wire thing for I2C. Justifies, in a way, having a 2-wire connector for MBUS also, which would be neater.
Although the CT itself needs only two wires, there may be instances where a shielded
cable and hence, a third connection is needed.
This is where - as Robert alluded to, above - knowing your market/audience helps.
None of the CTs Magnelab or Continental Control Systems sell, have connectors on the leads.
Most of the CTs suitable for use in North America, i.e. those with wire windows large enough to
accomodate the 4/0 AWG (~16mm OD) wiring commonly found in US homes have
“connectorless” leads.
Which is true if one knows how to solder, not a skill everyone has. (and even if one does, know how to solder, soldering said connector to the end of a cable isn’t totally trivial)
CTs from the aforementoned vendors with ratings as low as 5 Amps have connectorless leads.
Thank you Bill, that’s clear. Interesting points.
Can you elaborate on the type of cable used in North America? Do you have dimensions?
I agree soldering is not trivial.
@Bill.Thomson ChengHaoRan 1pcs 3.5mm stereo Adapter 3.5 audio mono plug to screw terminal Audio Mono Plug Audio Connector screw connector|Connectors| - AliExpress
Right, I’m off to the pub.
That not quite as would put it. It illustrates why the connector configuration needs to be flexible and not just be a emonTx v3 with more grunt.
There are many options here, to just dig in and stick with a ridged layout as it’s “good enough” for most users isn’t aiming very high. For example if you are absolutely adamant it should be set up for a specific user group then do so but at least build in some options for others to mod it, for example, put multiple footprints for various connector but just populate the mainstream ones, done well they can occupy the same space preventing “doubling up” and minimising the additional space required, it only costs some design time and some extra PCB holes. Or perhaps put a row of solder contacts and sloted cut-outs in the PCB so that the mainstream IO part of the PCB can be snapped off leaving a line of pads for other connectors top be attached via flyleads or an edge connector with a custum sub-pcb of their own design/making.
Have you considered making the comms between the RPi and the STM32 I°C or SPI or anything other than serial uart? There is only room for one serial device on a RPi GPIO, but there can be many I°C or SPI devices. Using the only available serial port is very limiting for expansion, eg if users want to read modbus, it will quite probably be via a serial adapter, or maybe they would like to continue using the rfm2pi board as well. Most RPi IO board and projects seem to revolve around the serial port, also theres the option of using a serial console ie plug a laptop directly to the GPIO rather than use ssh as is possible in stock Raspbian image.
is the Mbus on-board? If there was a well thought out header and the mbus was an optional additional plug in board, the STM IO and the 4 way connector could alternatively serve a plug in modbus board too.
Also is the Vref adjustable? The “other YDHC CT’s” you refer to as alternatives output 1v which is ill matched to the usual 3.3v inputs, as are many other CT’s. I think 0.3v is a standard output too IIRC, this was all previously discussed in great depth so that we could get a “good allrounder” device, your right perfect isn’t entirely possible but that’s no reason not to aim for it and deliver the next best thing.
We use Aluminum as well as Copper.
Aluminum is used for Service Entrance Wires (SEWs) UK term is incomers.
Wire larger than 10 AWG is of the stranded type, smaller than 10 AWG, is solid.
Copper is used for branch circuits. Unlike the UK, we don’t use a “ring.” Each circuit runs back to
a Load Center. (Consumer Unit)
SEW ouside diameter is typically 0.62 inches. (16mm)
Branch wiring varies a bit depending on the current rating needed for the circuit, with 12 and 10 AWG comprising almost all of the wiring in a typical residence.
6 AWG wire is used for cicuits that supply large loads, i.e. 30 to 50 Amps.
Ref: Wire Size and Insulation Diameter
Bill, I think he meant the twisted pair (black/white) from the secondary winding, that’s going to the p.c.b. (eventually, via the connector).
Quite a few times, I’ve fielded enquiries on the forum where users have asked for/asked about additional I/O capability. They seem to have looked at the Atmel 328’s capabilities and want to know why all can’t be used on the emonTx / emonPi (sometimes). In that respect, the emonTx V2 was superb.
It’s something to bear in mind.
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Yep. In that case…
Magnelab uses 22 AWG leads 8 feet long and CCS supplies their CTs with 18 AWG leads also
8 feet long.
(He may have been unaware of the CT wire-window size requirement over here. Now he knows) 