RJ45 expander - are all pins wired?


I have my emonpi on the way and I’m already planning my expansions :slight_smile:

I want to connect a pulse counter alongside a number of temp sensors on the 1 wire bus. I know that the relevant pins are exposed on the RJ45 connector (1 wire data : pin 4, irq1 : pin 6).

Can I use the following to break out both of those pins? (i.e plug my bus of DS18B20 onto one socket and my pulse sensor onto another)


The reason I ask is that this looks identical to this SWE2a Sensor Connection Module, Sheepwalk Electronics and that appears to only have 3 pins from each RJ45 socket connected.

All advice gratefully received.

Welcome, Mark to the OEM forum.

The description is “A 4-port RJ45 breakout board to allow multiple one-wire DS18B20 temperature sensors on RJ45 and optical pulse sensor to be easily wired to a single RJ45 bus for easy connection to the emonPi or emonTx.”
[my emphasis].

I have every expectation that it is suitable for both sensors at the same time (but of course you have only one pulse input - which implies that you can have only one pulse sensor, whereas the 1-wire bus supports many temperature sensors).

If you need further confirmation, I suggest you email [email protected]

If you look carefully at the Sheepwalk board, it appears to me to be double-sided (I see a via), and if that’s correct, there are more connections on the ‘top’ surface.

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Thanks for your reply Robert. Yes good point about the double sided board - that would indeed explain how it can meet the description.


Just to update this thread for anyone stumbling across it in the future.

I ordered the expander from Sheepwalk in the end (as I needed some other bits) and it worked perfectly for my 3 temp sensors and pulse sensor.

The RJ45 pins are connected as follows
1, 3, 5 - all connected together in common across all sockets (GND)
2,4,6,7,8 - all connected separately in parallel across all sockets



Can this gem be added to the shop site, to clarify?


Hi, I had the same question so pleased to have found this thread. So just to confirm, the OEM Optical sensor would simply plug into the second RJ45 socket on the sheepwalk board to allow for the concurrent optical pulse and multiple D18b20 sensing?

Given the water tank I’m monitoring is some way away from the Pi and main meter, I am wondering if an rj45 Y-splitter might work here to avoid a second lengthy cat5 run back to the main meter. Sorry, this is probably a daft question probably resolved with a pencil and paper.

Many thanks

I think so too. Look at EmonPi - OpenEnergyMonitor Wiki (the RJ45 details are quite a way down) and what’s written above.

Not written in the guide, but here Learn | OpenEnergyMonitor is about how to arrange the One-wire bus: If you have a lengthy cable, don’t use a “star” configuration, instead daisy-chain from one sensor to the next. Also see yesterday’s post 1-Wire Design Guide

great, thank you!