I am considering fitting a control unit for an external HotTub ....allows scheduling of heating time, temp etc all via phone app.
To work it comes as a 2 part module .. and RF Receiver at house end you connect by Ethernet to your Broadband Router. At spa end an RF receiver plugs into the spa control unit. Based on RS485 electrical standard.
The spa has external panels that are lined with foil faced insulation sheet ... will that block the RF ? I suppose I could remove the foil skin in a square aligned with the RX unit.
Many houses now have foil faced insulation - does this typically block RF ?
While your points re foil lining are true, I’ve not heard of it causing serious transmission / path loss issues.
Likewise, if the spa is designed to use the module ( as it seems), unless you’ve added metal screen not provided, I would assume the system is designed to allow for the losses.
Of course, there is the overall path loss- walls, free space ( well air), trees etc, boxes, …..
With a combination of power, low bandwidth ( low transmission rate *- the amount of data is probably small ) it may well be fine.
there is a rule / law, low data rates require a low bandwidth, this limits the required signal to noise ratio required for successful data transmission.
To some extent it will, and cutting a hole will probably not make a lot of difference. Line of sight is what you want,ie a high transmitter aimed at the maybe lower level receiver, but remember data has to flow both ways to keep it on the network.
I'm a little bemused, since if you have mains at both ends, why not simply use a hardware connection along the same path. Brian
People don't realise how much of an effect the *thickness* of the foil counts for. They seem to think any metallic layer, now matter how thin, blocks RF. That's not the case. The blocking relates to the thickness of the metallic layer and to some extent, whether it's earthed or not. All implementations vary in practice, too.
That's presumably the purpose of having cables on the two remotes. The household access point box, you can run the Ethernet cable to a spot where the Wifi module best transmits to the hot tub. This might include a glass basement window, as a location for the access point. The access point has a wall power supply. A line-of-sight install would be best.
Wifi modules have distance limits. The maximum is defined by some timer, waiting for a response. This is what was limiting the South American mountain top test, until they removed the timer from the code.
For reach, the access point does not have an obvious antenna or an SMA or RP-SMA antenna connector. So you cannot modify the radiation pattern. It might be nothing more than an Edimax 802.11N module used on RPi home builds, as an example of a Wifi module that is very cheap to buy. There's no sign of anything fancy like MU-MIMO (multiple antennas, some degree of protection from multipath issues). You may have to move the unit around, or rotate it, for best reception.
If someone stands in the path between the two units, the radio waves bounce off adjacent walls and signal still gets through. The Wifi signal is not as bad as routing a laser beam.
Some Wifi have adaptive power, and if they "hear" their mate, they will turn down the power level and not run the transmitter at max all the time. The worst thing for a cheap Wifi, is putting it in a Faraday cage and causing it to "scream to be heard" :-)
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The RS-485 is described here. The maximum serial communication rate is 10Mbit/sec but the thing likely runs slower than that. The signal is differential, on two wires, and the usage of such things is for noise immunity. Noise signals are imposed on both conductors (on the twisted pair), and the diff receiver subtracts the noise when figuring out the ones and zeros.
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It's unclear how they're doing phantom power over RS485. If that's what they're doing. Using four wires total would be so much easier. And the pictures here, inside the hot tube controller, do look like four wire (two signal, two power).
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At 2Ghz that's perfectly possible. I over-simplified. The frequency of the RF is very relevant here as well - PLUS the permitivity of the metallic layer (IIRC it's permitivity; could be permeability - been a while since I looked into this.) This is why the best RF spectrum analysers were *very* heavy indeed. They have excellent isolation WRT the outside world due to the *thickness* of the shielding used in the casings.
Easy to give a definitive answer: aluminium foil severely dirsrupts RF transmission in the upper MHz/GHz range.
I have in my house. It causes serious transmission / path loss issues.
My oil tank sender fails in windy weather - its less than 20 meters away
- because of weak signal and multipath, compounded by the foil backed plasterboard the house is lined with. Modern electronics is designed to sell. Not to work.
'May' being the operative word
No, low data rate does not require low bandwidth, it does not require high bandwidth.
How that is taken advantage of to improve signal to noise, is quite a different matter, if indeed it is
Er no. Google 'skin effect'. I can assure you that tinfoil at thou thicknesses effectively blocks radio signals. just as people have need screening RF circuits in tinplate cans for *years*. Ocv er 100 years in fact
I suppose an 'option' would be use an extension RS485 lead (alternate lead) on the Hot Tub to controller. I could then site the unit outside the Hot Tub, avoiding the foil insulation.
Is that plug type standard for RS485 (or does standard only specify data signalling)
I'm pretty sure the kit seller would not sell an extension lead. The standard does state it supports long cabling distances
Is that a definite fact? I've looked at the website, and it's all about using a phone to access a wifi router cabled to the house end unit. Nowhere could I find any statement of what travels between the two boxes.
You don't need a lot of bandwidth to turn on and off a heater and lights. 300 baud would be entirely adequate. I would suspect the boxes communicate at much lower frequencies, using something like the XBee at
868MHz:
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These boxes do that, at 9600 baud, using older 434MHz modules:
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They use antennas because the boxes are quite thick milled aluminium.
The very cheap Chinese 434MHz modules would probably work. The trick would be writing software to drive them, as they are bare transmitters and receivers. The XBees Just Work.
As they discovered with undersea telegraph cables, you can get hundreds of miles by pushing enough voltage in a cable to practically melt it. Signal to noise, chaps. More signal means better signal to noise. In the end a twisted pair resembles a transmission line, so it attenuates high frequencies not much more than low ones.
ADSL nets you several Mbps over a mile of twisted pair, for example.
Back in the days of mincomputers and glass serial terminals an office block could run them all at 9600 no matter what.
I'm not sure I would agree with that. The attenuation of copper transmission lines is roughly proportional to the square root of the frequency. It is remarkable that ADSL and VDSL work at all. They do need huge amounts of equalisation to get the higher frequencies through twisted pair telephone wire. I am on a G.FAST cabinet, but the service is not available to me because the high-frequency attenuation of the twisted pair is too high at a range of about 500m. John
This is what happens, when as a company, you contract everything out. The hot tub turns into a science project. It's really hard to tell if the parent company, knows anything about what it is selling. I could understand this level of skullduggery, if they were charging a monthly fee for the "cloud integration".
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Someone here thinks they used Bluetooth. Based on poor reach.
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The other threads think it is Wifi. Wifi needs different band plans, depending on what country you are in (there is a one channel difference between NA and UK).
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You can see these people enjoy themselves.
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This is the trivial part, except when you're reverse engineering what was done.
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And they say at one time, we landed men on the moon.
Think how easy this would be, if the hot tub had an Ethernet cable on it. Which is differential and not ground referenced (transformer isolated). At least some parts of the Ethernet protocol, are old hat. Ethernet has CRC and retransmission of packets at hand.
Spa end unit connects over RS485 cable onto existing control unit, it communicates back to the house unit which is cable by Ethernet into BroadBand router.
That way App access Spa over internet.
AS to what frequency or BitRate, I have been unable to get that information,
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