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Hardwired Temp/Humidity Sensors

NikoFL | Posted in General Questions on

I’ve been looking for a while for a system that has hardwired temperature and humidity sensors that I can install in different hard to get to places in my house. Basically a system like Govee or other but instead of battery operated WiFi sensors I’m trying to just have it hardwired and powered by a permanent power source.

has anybody come across a system like that?

thank you in advance

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  1. Expert Member
    DCcontrarian | | #1

    I use these sensors:

    You can run them great distances using ordinary thermostat wiring. I'm a nerd, so I run them into an Arduino which I've programmed to upload to a data store every ten minutes.

    I'm hoping to make this a shareware project eventually so I'm happy to provide more detail.

    1. NikoFL | | #2

      This is great. I’d love to learn more. I have a computer science background so totally down to nerding out on this.

      Please share away.

      I’ll go ahead and order these.

      Thank you

      1. Expert Member
        DCcontrarian | | #5

        Respond if you want to email me to discuss further. Thanks.

  2. Expert Member
    Akos | | #3

    I've ordered standard 4-20ma sensors from Aliexpress, these are around $20-$30 each. Most can also do 0V-5V or even rs485. I've been using these to control the ERV in my home.

    Instead of wires, I've taken the standard wireless sensors, got some NiMH batteries and connect a mini 5V solar cell to trickle charge them (also needs a diode in series otherwise the PV cell will discharge the battery overnight). This combination has been running for a couple of years now outdoors without issues.

    Another option is to get some Sonoff units with a THS01 temp/humidty sensor. These can be powered from a cord and are pretty simple to integrate with most home automation.

    1. drewintoledo | | #10

      Akos - if I understand correctly, I'm curious why you're using an ERV with humidity sensors instead of an HRV?

      1. Expert Member
        Akos | | #11

        I run an ERV because I like to keep the house around %45 RH in the winter time, an HRV would dry the air too much, even the ERV starts cycling when the temperature get really cold.

        The humidity sensor is there because it was essentially free when ordering. I also have a program to flush the house if it is too warm inside and the RH and temperature is low outside. This rarely happens so it was a bit of waste to even program it.

        I'll eventually pull out the sensors and replace the PLC with a simple countdown timer for boost as it is all I really ever use the controls for.

  3. Expert Member
    BILL WICHERS | | #4

    You might want to try the Dallas Semiconductor (now part of Maxim Integrated Products, which is itself now part of Analog Devices) "One Wire" devices. They make some DS18B20 sensors that are very small, relatively cheap, and capable of working with reasonably long wires. As far as I know, there is no humidity sensor option for that product line though.

    Another option is to build your own networkable controllers. Some years ago, I designed and built a few temperature and humidity sensors using a temperator sensor from National Semiconductor (I think an LM98, but I don't remember the part number), and a humidity sensor from Humirel. I used an RS485 serial network. I wasn't entirely happy with that system so I redesigned it using the same sensors but a two wire combined power and data network. A PIC microcontroller was the "smarts" in the remote sensors. A simple addressable network protocol worked by sending data to the sensors by varying the supply voltage to the two wire network, and the sensors replied back by modulating their current draw for the master controller to read. The purpose was to create a cheap, but high density, sensor array for monitoring thermal gradients across rooms in a telecom facility. The two wire system was more flexible, easier to wire, and functioned the same. Something like that might be an option for you if you can't find anything you want already made into a product.

    I find that many of the "small" sensors are overly complicated, using wifi and other fancy systems that are way more than what is needed for a temperature monitoring system. Using a simple wired network using boring networking systems like my two wire system, RS485, or Dallas's one-wire (which really uses two wires, BTW), are much better suited to such systems. You want the networkability to allow a single bus-type wiring topology to be used to address multiple sensors. Home runs from each sensor back to the master controller makes for overly complex wiring if you have more than a few sensors.


  4. user-7047834 | | #6

    Sorry that this a very different direction than where you seem be heading, but we have a high quality oven thermometer (the kind you stick in your food to see the temp inside). It reacts very quickly. When we wonder what temp a room is, we walk in and turn it on. Works for us...perhaps it would work for other non-tech folks.

  5. DennisWood | | #7

    You can connect up to six DS18B20 temp sensors to a Fibaro Smart Implant (zWave device) so the implant is powered, but communicates via zWave. About $100 all in with six temp sensors. I use these for my HRV setup and pool solar. Very reliable. Attached is the Hubitat (automation hub) dashboard for the ventilation system. The HRV uses five sensors, one on each air stream and one after the fresh air heater setup.

    Each sensor can then be used to trigger automations, do efficiency monitoring etc. on the Hubitat hub. The Fibaro devices work on quite a few different hubs aside from Hubitat.

  6. Expert Member
    BILL WICHERS | | #8

    If you use those little Dallas one wire sensors, you can use simple cat3/cat5 cabling, but you get get a little better performance if you use low capacitance (so called "low cap") control cable, which is available from commercial wire and cable suppliers.


  7. user-5946022 | | #9

    I use these - they are powered via USB, so can be via regular outlet with an adapter, or with an outlet with a USB plug. They communicate wirelessly via z-wave to my Hubitat. Once paired, Hubitat collects the data, and I can graph it or set automations to act on the data (such as turn on dehumidifier when humidity reaches x, turn off when it reaches x-4%, etc.)

  8. steve41 | | #12

    Are these sensors appropriate for in-wall installation? I still have open walls/ceiling in my addition. It's been on my to-do list to research options for monitoring in-cavity conditions in a few areas. I envision pin type moisture sensors permanently installed in cavities in 6-8 places that are more likely to experience issues.

    1. Expert Member
      BILL WICHERS | | #13

      I would expect the pins to deteriorate over time and start to give erroneous readings. That's the one big question mark for mositure monitors in long term applications for me. Using a high grade stainless alloy like 316 would probably help, but a real lab setup would probably use platinum.

      Temperature sensors should be fine. I used an LM34DZ (analog sensor that is otherwise pretty similar to those one wire sensors) outdoors for around ten years and it was fine the entire time. The humidity sensors have always given me problems in harsh enviornments though.


      1. steve41 | | #14

        Thanks Bill, good info. I'll do some research and see which direction seems best.

  9. DennisWood | | #15

    Steve, the DS18B20 sensors are rated for immersion (I use them in salt water) and are just fine down to -30 C. The end probe is stainless. If you use them, I'd expect no issues. About $12 for three of them:
    You can connect six of these to one Fibaro Smart Implant.

    The DHT22 measures both temperature and humidity but you can only connect one to a Fibaro Smart Implant:

    A Fibaro Smart Implant is about $39 but you'd need to add a 12 V DC wall wart to power it. These ones work well:

    Putting probes in the walls is 100% something I would do in new construction, particularly if I was using a non-conventional wall type!

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