So, I picked up an Eastron SDM220-Pulse energy meter from China:
Aliexpress SDM220-Pulse link
Which is a DIN rail mounted power meter, I see some people in Europe are using the 3-phase versions for their monitoring but using the RS485 output. I bought the Pulse version, which looks to have the RS485 actually there but not labelled - RS485<-> USB interface in the post at the moment to test that theory.
It looks to reading this manual I found that it has a passive pulse output, so I feed in voltage and count the pulses out.
Reading the wiki page for optical sensors (now linked thanks!) page it would seem that I can just connect:
SDM220 Port 5 (Pulse -ve) = EmonTX Terminal 2 (3.3v)
SDM220 Port 4 (Pulse 1 +ve) = EmonTX Terminal 4 (IRQ1)
And I can then count 1/1000 imp/kWh like I would with an optical sensor - is anyone using the counting like this and confirm - or anyone with more experience than me on the EmonTX point out if I got this wrong?
If the “passive pulse output” is a switch (optical or mechanical), then there’s a lot about pulse counting in relation to gas meters over in the old forums. If it’s a semiconductor switch (i.e. the receiving side of an opto-isolator), then the polarity of the terminals will be important, but de-bouncing won’t be necessary. The meter manual isn’t clear. Also check which terminals you need on the emonTx - I think it’s 2 & 6.
I took the pins from the optical page which were for 3.2 it said, v3.4 [EmonTX Wiki Page] (EmonTx V3.4 - OpenEnergyMonitor Wiki) and this table says:
emonTx V3.4 pulse-counting screw terminal connections
Screw terminal pin Connection
1 5V (if powered via 5V USB)
2 3.3V
3 GND
4 IRQ 1 / Dig3
Which seems its 2/4 - You may be talking about the RJ45 which is 2 & 6 and I am talking about the screw terminals?
Polarity is marked on the side of the monitor, there are two pulse output one fixed at 1000imp/kWh and the other configurable, they share a common -ve or input, see picture:
Will go read the gas meter counting, I need to check into that as it looks like our gas meter may also have an optical interface from the markings, but I can see no obvious LED.
Yes, it is 2 & 4 on the screw terminals. Note the top legend/silk screen on the pcb for terminal 4 is wrong!
There won’t be a LED on a gas meter - no electrical power (obviously!), what you’ll have is either a reed switch or - less likely - a reflective optical sensor that requires power. A reed switch is bad because it will need de-bouncing, anything optical will be not good news for battery life (though you can pulse the emitter and the sensors, which will give a useful improvement).
I ordered my EmonTX in a case, so lets hope the acrylic panel has the right numbers 
Stupid statement I made about LED right! It says on the meter “Pulse=0.01m^3” but its no obvious where you get the pulse from - I need to google the model when I get a minute.
… and it’ll need to come out to get at the terminal screws!
I may even re-mount it in a plastic IP box to keep the dust in the garage out of it, but I didn’t want to make the mistake I made with EmonPi of ordering bare then just buying a case later as I ran out of time to adapt/make one so ordered complete this time 
Need to finish pulling the new 16mm2 SWA submain through garden into garage before electricians come to connect it up and install EVSE first 
With some luck the cheaper “pulse” unit also has the RS485 stuff inside and I won’t need to count pulses anyway.
@TrystanLea I saw your tweet about “EmonESP” are there any more details anywhere? I just started working out how to take RS485 from the SDM220 into an ESP8266 directly back to EmonPi - but if you have a canned solution all the better!
Cannot see any code in GIT at the moment, what dev board are you using?
