As the header says anyone know any technical details of how the system works. Ok I know there is an RF signal from the sensor to the receiver. Trying to help a mate who wants to connect to a computer, either by modifying existing receiver or using a different RF receiver and decoding the signal sent.
Any sensible ideas happily accepted.
It should be working in either Category 1 or 2 of the frequency ranges stated in the License Exempt Data Link Apparatus which is:
Category 1 Apparatus designed solely for use within one building is set at between
2.445 through 2.455 GHz using an output power at the transmitter of up to 100mWCategory 2 Apparatus designed solely for use within one building is set to between
10.675 through 10.699 GHz using a power output at the antenna of up to 1WIt's these ranges that are holding back the wireless alarm systems sold around Europe at the moment, but they may allow the frequencies to be expanded shortly to allow for more ranges to be introduced. So if you can find out what power is transmitted at the sender unit you should be able to find the frequency the system uses.
You can contact the sales team for these units on snipped-for-privacy@sensor-systems.com for more details on how they work.
Sorry, should also have given their website address as well:
2.445 through 2.455 GHz 10.675 through 10.699 GHz
Last time I loooked I was fairly sure they operated in the UHF band
433 or 418MHz but they do keep messing about with what can and can't use these ranges. This allocation wouldn't be any good for the quoted 1km range that some of their products now have though.It might be easier to get the "Signalman" product and get it to call your own computer rather that the suppliers. How easy it will be to reverse engineer the data it needs to be sent and sends back is another matter...
I doubt if the makers will be prepared to release the tech details. (ICBW) Geoff may have had one to bits perhaps but your best bet may be to find the
7 segment display output within the wall wart box and take your info from thereIn message , John writes
No, never seen one, but I'd just open it up and have a look inside if I was going to do what the OP wants to do.
It will be working at either 433 or 418 MHz. Maplin sell receivers for these frequencies which you could connect to the serial input on a PC and try to analyse the data stream.
That is my understanding too.
It transmits a short burst every minute or so I think.
I have one of these on a 3000 litre water tank. When installing it, one must calibrate the sensor.
The sensor is a sonic measurer that transmits to detect the liquid surface. Once the system is calibrated and measuring, it only transmits once ever minute or so. The time taken for the pulse is gated into 10 readings and these are then transmitted by radio to the receiver.
No ideas how the data stream is coded.
Peter
Don't know the system at all, but if they are marked "patent pending" etc , it might be worth a search at the patent office site:
If there are US patents, the
"coherers"
I played that game with the Oregon Scientific remote thermometers. Actually, a trawl around the web revealed someone had analysed the protocol for that, not fully but well enough. A scope on the output of the receiver in the Oregon Scientific showed a nice square wave digital signal appears when one of the transmitters sends data. However, a scope on the output of the 433MHz receiver I bought (CPC) just spewed garbage -- the digital signal appeared during reception but I didn't fancy trying to separate it from the noise. If I was going to persue this, I would probably by another Oregon Scientific receiver just to steal the 433MHz receiver out of it. In the event, I decided to do it all a different way (which is more accurate, more reliable, and cheaper than using the Oregon Scientific units).
The noise will possibly be the coding - could be RTZ (return to zero), NRZ, (non return to zero), Manchester encoding or a few others, plus then the data will possibly need to go through a UART to translate the HDLC protocol.
There isn't a continuos carrier with these systems, many Tx/Rx pairs share a common frequency. Each Tx only transmits for a short period (
Have more dtails now.
The frequency is 433.92 Mhz. The receiving end has a generic UHF data receiver probably same as used everywhere. This then feeds into a PIC chip (surface mounted). This drives a single digit LCD display. Also has a dual op amp and a voltage regulator. Transmission interval appears to be more like every 15 minutes once initialy calibrated. Has three uk patents GB2318696, GB2302178 and GB2303920, looking these up did not elucidate much details, 2 are for the sensor syetem bit and the other for an RF transmitter.
Anyway sounds like no details out there yet, I do like the idea of dialing own computer and parially the see output from chip.
Thanks everyone now back and talk to my mate who wants to link into a home automation setup.
Have you considered asking them for the protocol. Not sure how it would damage them if you used it to connect to an automation system as they still sell the kit with the tank AND it would look good as a press release.
FWIW this is fully decoded now and working with the rtl_433 software on Github. You can receive the Watchman signals with a £10 USB DVB-T receiver dongle...
How accurately are you able to measure the oil level? Nearest mm?
About the nearest centimetre. Which in a 60x180x120cm tank is about 11 litres. But it's good enough ? I'm not after precise usage of a per iod of hours; I want to know when I'm going to need to get more oil delivered. And it works fine for that.
With it all hooked up to the home automation system, I get this kind of thing:
See
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