Cheapest temperature sensors

For my home project I have been looking at the cheapest way to monitor temperature sensors throughout the house. I am thinking < £20 per sensor given I need about 8.

I had originally started with the idea of having a temperature and motion detection (to see if someone is in a room), eventually I want to control heating.

I heard imagintronix sensors are quite cheap (< £10) but not found much about hooking these up to a raspberry pi. I bought a TI SensorTag, these come out at about £20 and have 6 sensors but I am only using the temp one, this talks over Bluetooth Low Energy (BLE) direct to the pi BLE dongle and with a bit of programming (2 hours messing around) I got temperature readings from it. I still need to do some work to find out if I can get continual readings and also if I have 2 of these I can know which is which (probably mac address or something like that).

It seems if I get into Arduino boards then I might be able to make something but was hoping for something that is already consumable that I can hack the wifi/rf signal from.

Any ideas?

Hey ex...

That you on the LWRF forums?

If you want simple temperature monitoring, the best way would be something like oregon scientific (or similar) coupled to an RFXtrx433.

Due to the way the 433Mhz air waves are used, there are limitations to what you use, how many etc.

The cheaper one's (around £15-20) permit 3 per localised install (channels 1,2,3).

There are slightly dearer one's (around £25-30) that permit 10 per install (channels 1-10).

I think, that for the moment, wifi based sensor's are impractical due to the power requirements.

Yes it's me on lwrf

I had a wireless keyboard for my htpc which i guess was operating on that bandwidth and it was always playing up so am slightly nervous about using that technology, I guess also neighbours devices can interfere too but cheap is good if it works.

Is there a distance limitation with those oregon or other devices?

Is the RFXtrx433 used with domoticz on the pi, is that what you would advocate?

Have you played with a sensortag on BLE? They are quite cool actually and I think quite accurate based on my tests. BLE can apparently go up to 60m. The dongle was £12, so for < £40 I had my first working temp sensor.

Hey Andy,

Ha, thought it was you... cool ID btw lol.

The distance issue is one of the carrier frequency, but as things go, 433Mhz travel's quite well.

The RFXtrx433 is a popular transceiver, likely one of (if not) the best.

I know user's do use the RPi with domoticz and an rfx coupled up, but in all honesty, the RPi is a limited device, certainly not enough power to run BMS Link.

I did try in the early day's (as well as a variety of ARM based devices) and none of them will do it.

The smallest device I had true success with was the intel NUC, but having a system tied to hardware made no sense, hence the virtual machine route.

I (like a lot of people) have a PC that run's 24/7, so my BMS Link just sit's on that.

Regarding the interface's (RFXtrx433, Zstick etc.), for the best performance you really need these situating mid position within the building.

Direct connection to your PC will likely not allow this, but there are other ways

Since BMS Link release, I (and my user's) have been using a network/usb server, which works automatically, but i'm about to depreciate this in favour of using the RPi as a device gateway.

I've been testing this method for some time now and it works very well.

I have the RPi in the kitchen, above a wall unit and it has the RFXtrx433, Zstick and RaZberry installed.

BMS Link finds these automatically, connect's them to the system and starts the relevant interfaces.

All good

Not heard of the BLE/sensor tag route, to be honest I've been pro Z-Wave for sometime now.

I'm an automation/electrical engineer by trade and I have to say its on a par with the sort of gear they'd expect on commercial installations.

Not sure what you're trying to achieve with the temperature monitoring, but when I used the 433Mhz route, it was more expensive than using a Z-Wave controller and fibaro motion sensor, which measure temp and lux level's too

Neil, very helpful post! You have given me loads to read up on, give me a day or so and I will do some reading so I can answer a bunch of questions myself and save you the time.

For my initial project I just want to monitor temperature in multiple rooms over a 3 storey house. My intention is to manually adjust the thermostats to try and get an even temp across all the used rooms. I don't think I want to control TRV's. However, I do want to switch on/off heating to replace or add to my digital thermostat (a typical programmable Danfoss one). I would like to do this based on whether I think anyone is in the house - smart phones are a great way to do this but also wanted to check for movement in rooms.

I am a computer scientist, always been windows software development though, have built my own arcade machine and generally like projects which push the comfort zone. The Pi is new to me and my electronics is limited but growing (but for example I would do most electrics in the house), am not in a rush to start playing with switched 240v! The driver I also have is that my lounge gets a bit cold, so hopefully by lowering TRV's elsewhere I get a warmer lounge at lower cost!

Hey Andy,

PIR's for enabling/disabling room's could work, but central heating tends to need a good run up before you notice any benefits.

I already use mobile device detection to automate my heating. The annex is enable/disabled by my lads iPad (with override's too) and if the system detect's no mobile device's, it put's the master thermostat into a set back mode (also with override).

Am thinking more about when only the kids are at home, in their rooms with phones out of battery (my daughter most of the time!) vs no one at home, at the moment am thinking only turn on/off whole house heating. i.e. nest style (am assuming these tado/nest devices are learning somehow if someone is in the house).

Maybe the PIR is a step too far, and I need to tell my daughter to charge her phone which will provide heating - that will confuse her!!!

I think Nest just tries to learn a pattern based on how you change the stat setpoint yourself.

Tado use's your mobile phone's locations (via GPS) to switch between a setback (away) and normal (at home).

I can (and will soon) allow for polling this tado setpoint and of the 2 tech's, its the one I'd consider.

I assumed based on your bmslink guest login and the phones at the top that is what you were doing, no one at home, heating off.

Lux is an interesting sensor though, no lights on, no one in room, possibly.

What is the model number of the fibaro temp+lux sensor you refer to?

yes i do (with the phones).

yes, the fibaro sensor is here...

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i think i might order one of these too

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maybe this one too....

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I have their door sensor and that works well

Ah, sorry, GPS position, not connected to local wifi I guess?

Tado benefit from their app being installed I guess on their users phones.

Hehe, just added a new idea to my project

£50, £45 and £34, getting expensive when times by 8. However, 1 would of course could be an exploratory purchase!

Are there any limitations to be aware of like the channel limitation on the cheapo temp sensors we discussed?

The Z-Wave system permits up to 232 (if i recall right) nodes per controller.

I think the vision sensor is a good price for both temp and PIR.

The equivalent for 433 would be the oregon sensors (£30) plus marmitek pir (£30), but it won't work right as the 433 system mean's sensor's can block each other, meaning you miss triggers.

Hey Andy, you on skype?

No, working, and sneaking replies as I go!

hah