S0 electric meter with multiple S0-inputs

[slowfinger]

Hello
1st to apologize I am not an electrician so pls forgive me..

I have 2 electric meter with S0-outputs (1x electricity used, 1x electricity produced by solar panels). These are coupleed with eltako FSS12-12VDC Enocean counter with my Raspi (FHEM) and are working fine.
Now I wanted to use these S0-ouputs additionaly in an ESP8266 D1 mini with EasyESP. Final goal would be to have a 4x20 I2C LCD showing electrictity used/produced and to send available energypotential to a powerwall/charger for electric vehicles to adjust loading current ...

Therefor I connected

S0+ o (FSS12)
|
S0+ o-----------------o +3V
S0- o-----------------o GPIO
|
---4,7kOhm---o GND
|
S0- o (FSS12)

==> even if now two counters (FSS12 & ESP8266) are attached this is still working fine.

If I want to add the other S0 counter the same way the pulses are messed up (FSS12 are still attached, but to simplify the are not shown below) and I get the sum of both counters on both GPIOs (and on both FSS12)
S0(a)- o-----------------o GPIO(a)
|
---4,7kOhm---o GND
|
---4,7kOhm---o GND
|
S0(b)- o-----------------o GPIO(b)

S0(a)+ o--------
|
S0(b)+ o-----------------o +3V

Would optocoupler help ? How should they be implemented ?

THX
Slowfinger

[Shardan]

Hello,

as i don't have a FSS12 at hand for testing i have to guess some things.
Please be aware that I do some practical prophecy here.

So from the datasheet of the FSS12 i guess the internal circuit might be as in this pic:

Counter-FSS12.jpg (34.34 KiB) Viewed 2878 times

It might be possible to attach an opto coupler here but i guess the internal resistor inside the FSS12 is too high for that.
An easier way might be the following circuit attachment:

Counter-FSS12_With-ext-circuit.jpg (46.87 KiB) Viewed 2878 times

It uses a cheap NPN transistor as a BC107, BC547C, 2N2222 or something similliar as an impedance and voltage adaptor.
When the level from the counter is "high", the S0+ has around 12 volts so the transistor is open and pulls down the output to "low"
If there is a pulse from the counter and the S0+ is low, the transistor goes to high impedance and the GPIO is pulled to 3,3V by the 10K resistor.

There might be another problem. I don't know the internal circuit from the FSS12 so I can't say if the ground is free of any external electrical potential.
If not this may lead to unpredictable behaviour. In this case an opto coupler is necessary. As said i doubt if the output can drive an opto directly.
You may use this way instead:

Counter-FSS12 with Opto.jpg (56.87 KiB) Viewed 2878 times

In this circuit the transistor drives the optocoupler. It's a cheap 817 type (LTV-817, LE-817, PN-817......)

Hope that this helps

Regards
Shardan