OpenEnergyMonitor Community

emonTH2 multiple temperature probes

Is there a sketch for connecting more than one DS18B20 external temperature probe to the emonTH2 whilst retaining use of the onboard Si7021 temperature sensor?

I would like to connect up around 4 or 5 external probes in addition to the onboard sensor and have logging at least every 15 seconds. The reason, to monitor my combi boiler flow and return temperatures, cold water inlet temperature, hot water outlet temperature and outside air temp from the rear of the house, in addition to the kitchen temperature and humidity using the onboard sensor. Of course, powering the whole lot from a 5V DC supply rather than AA batteries.

I saw this: ARCHIVE: : emonTH Multiple DS18B20 Sensors
But I assume this applies to the older emonTH with the onboard DHT22 sensor so wouldn’t work with the later emonTH2?

The reason for wanting to check, is to ensure the combi return temperature is always kept below 54C so that it is condensing and running as efficiently as possible and to see how low I can go for a given outside temperature to improve efficency whilst maintaining a warm house!

I’m sure others would find it useful if monitoring a heat pump (flow, return, brine in/out, DHW, air) but without the extras of the emonTx or the heat pump board.

I don’t think so, but it should not be difficult to add that to the ‘standard’ sketch. Looking at the sketch, there’s “partial” provision for 4 sensors as it is, but only one external sensor’s value is transmitted. Why it’s been done like this, I’ve no idea.

That’s correct - and the claim that it can handle 60 sensors is a little far-fetched, as that exceeds the capacity of JeeLib, the library that handles the radio transmissions.

I could modify the sketch if that’s what you’d like, but I don’t have 5 sensors to be able to test it.

I’ve ordered some temperature probes & another emonTH. Had a look at the sketch so will have a play around with it myself first. Best way to learn! If I’m stuck, I’ll be back :smiley:

If you’re having 4 or 5 DS18B20s, I’d strongly recommend saving or hard-coding their serial numbers, because if you need to replace one, the order in which they are found, read and reported will change around, and cause endless confusion. (See ‘Learn’ for how this happens.)

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Did you get anywhere with modifying the sketch?


TrystanLea did a sketch the other day which I used successfully. It’s here:

If you do not need battery operation, I’d use a Wemos Mini D1, and Tasmota.

Just found your post, and I’ve just done what you are describing.

I wanted to see exactly what was happening with my heating system so I’m using an emontx to measure boiler amps, inlet flow temperature, and outlet flow temperature at the boiler.

at the Bypass Valve which is around 10 metres from the boiler I use an emonTH to take four measurements which are feed and return 1 metre before the bypass pipework and the same 1 metre after the bypass.

From all this data I’ve been able to determine a better setting for the bypass valve. Also, from boiler current, I’ve been able to come up with a calculation to determine its firing rate as a Percentage, and from that, I’ve worked out the daily kWh gas uses to within ±1kwh.

I took an emonthv2 and fitted it in a larger case. I then wired 4 DS12B20’s into a single terminal rail which then connects to the original emonth PCB connection rail. That way I’ve had no soldering to do.

Yes, the emonth V2 firmware was confusing as it saw the four probes but only used the data from one. So I butchered the firmware to do the job myself. It’s probably not pretty but it working. I’m running on batteries at the moment and I’ve sending data every 15 seconds so I’ll probably power it from a 5V source if I’m keeping it in place.

Gas Usage per day kwh.
gas used

Boiler signals