temp/humidity sensor advise

[brjhaverkamp]

Hello all,

I just got started with rflink, controling/reading my 433MHz devices with domoticz.
For temperature and humidity I had a couple of wt440h devices. But they have poor range, which was confirmed by googling for them.
and most of them I can not reach.
I like the formfactor and the display for local readout though.
Does anyone have an advice for something similar that has a decent range, records temp and humidity (at least) and has a local display?
Oh and works with domoticz/rflink gateyway of course:-)

Regards,

Bert

[mtsinc]

One of your biggest problems is that the 433 MHz band is actually the property of the Amateur Radio Service in the USA and "shouldn't" be used by unlicensed transmitters.

However, obviously it is and quite freely. So how?

As it turns out there's a loophole. As long as your transmitter power level is low enough, and your transmissions are infrequent and short, it's allowable. That means that one-shot devices such as garage door openers get a pass, as do environmental sensors which generally send out a small packet once a minute or so.

The killer part is the power limitation. Since transmitter power is restricted, the only ways to increase range are by more intelligent uses of antennas, more sensitive receivers, and/or more cleverness in the protocols, since 433.92MHz is pretty noisy (at least around here).

I've been playing around with 433MHz LoRa, but I'm building custom units and we're still trying to figure out how to get Domoticz to discover them. LoRa has a range of half a mile or so, since it uses spread spectrum and other tricks to get around noise issues.

For more mundane uses, you're limited on what you can do with the transmitter and its antenna, but upgrading your receiver is an option. Use a better quality receiver (some of the inexpensive chip units are awful), and a good antenna, well-aimed.

[Toulon7559]

Generally the improvement should be achieved at the receiver-side.
RFLink Gateway + this kind of antenna is already superior to the 'standard-RFXCom-kit'.
A groundplane antenna is even better than a dipole.

Quite a lot of T/H-sensors are compatible with RFLink Gateway (regardless of the antenna-type):
look in Supported Devices and then at a supplier's webshop
Be aware that some of those T/H-meters have a choice of 3 operating channels and other T/H-meters provide 5 operating channels.

[brjhaverkamp]

hello mtsync,

I don't think this is an issue for me. I am located in Europe. Here 433MHz is in the ISM (Industry, Scientific and Medical) band in ITU region 1. The usage is very similar to 315MHz in the USA (although that is not officially a ISM band, I just read). The devices are very common here.

Lora is great, although I think it is overtaken by NB-IoT and LTE-M now from the mobile operators. But I wasn't looking for that kind of extended range. I just need coverage around my house and in the garden. This is about 50m real life (not free space) .

The antenna that Toulon shared are a good idea. It will also give me some flexibility to locate them in a better place.

I'm currently eying the Cresta TX 320. They are "reasonably priced" and I hope they have better reach than the WT440Hs I have now.
If anyone has real life experience with this one, I'd be happy to hear. Other alternatives as well.

Regards,

Bert

[rv24531]

I believe what mtsinc was trying to say that since here in the US, the FCC has 'hard limits' of how to stay inside the loophole and get FCC Certified, all manufactures have to play within those limits. So brand A, brand D and brand Z, should have about the same coverage. Think about it like this, a 1.2v battery from any vendor SHOULD be 1.2v, if they want to stay authorized as a 1.2v battery.

In the radio world, there's two things that make the biggest difference, location and antenna. If you can't hack the hardware to change the antenna, then hack the location Either try to move the transmitter closer, or higher, or the receiver. sometimes just a foot one way or the other can make the difference in a signal being heard or not.


Actually, if I may make a suggestion .... try RTL_433 on a raspberry pi ( https://github.com/merbanan/rtl_433 ). Keep your existing hardware and displays that you like, and use a RPI with a SDR and RTL_433 with a magnet mount antenna and you'll be picking up 433 devices from around your neighborhood. That data, with a little effort, can be fed into Domoticz without any problem. Just double check and make sure RTL_433 supports your hardware to decode (Probably does, there's a TON that it supports).

I'm actually using a Pi and RTL_AMR (Automatic Meter Reader) to read my energy and gas usage, and feeding it into Domoticz for logging. Truth be told, I could just as easily feed about 20-30 peoples gas/power meters into Domoticz, all because of the antenna that I have hooked up to the SDR. Like I said, location and antenna

[brjhaverkamp]

hi Rv24531,

Thanks for your reply. I don't quite agree with you on your verdict of the different devices. As you say, the antenna is one of the main factors. Lots of consumer electronics producers are not very good at designing/testing antennas. If it works, it works..
From my experience (I have worked at a mobile network operator): Even in devices where it matters significantly, cell phones, the difference in antenna and hence reception of phone calls differed significantly. The power requirements like posed by FCC are normally at the input of the antenna IRC. Agreed that that should be similar for the devices. But the coverage can still be different

So I think there could be quite noticeable variations as well in these kind of 433MHz temperatre sensor devices.

Your remark about location and antenna is absolutely valid! And I am aware that I have a sort of worst case situation. I have my Rpi and Rflink gateway in my utility cabinet which is on the far corner of the house, next to the frontdoor. Add to that a 1930's house with sturdy stone walls and concrete floor, there is not much chance the backgarden sensor can be reached.

Hence the pointer from Toulon about the added antennas was very valuable. I am still doubting between the groundplane and dipole antenna, but one of them will make a good Sint Nicolaas present this year:-)

Cheers,

Bert