Stable RF

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RustyH

Senior Member
Good Evening All, hope everyone is well

Been meaning to look at this project for a while, but its been heightend due to had robbery at my neighbours last night.

I was to design a few trap systems for some vunerable places around my garden. Such as fences, garages, etc.

I want to know what would be the best method for sending data from say the top of the garden to the house (25-30 meters). I say data, it will just be a on (activated) / off (idle) signal, so very very basic?

Cheers
 
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nick12ab

Senior Member
So it only needs to be on or off - that makes it quite easy.

The simplest method would be to use 2 wires. The 2 wires should be shorted when not activated and open (not shorted) when activated so that it becomes open if the wire is sabotaged.

If a wireless system is required then there are lots of options - try searching the forum - but I cannot make any suggestions other than don't go with a simple carrier on/off as the thieves could replicate the simple signal while they go and perform the robbery - or perhaps not as you haven't said anything about them.
 
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PaulRB

Senior Member
Infra red? Will you have line of sight to the house? There must be ultra-bright ir leds available these days, and with a small reflector like you would find in a torch, you might focus this towards the house...
 
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RustyH

Senior Member
Im not sure a line of sight might be maintained, so prob have to rule IR out

In terms on the on or off, I meant thats the only information I would want to send over the wireless system, so it doesnt need to be a highly complex method sending loads of data
 
hippy

hippy

Ex-Staff (retired)
You could just run cable from the sensor to the house, have the job done while still trying to figure out how to do it by wireless :)
 
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g6ejd

Senior Member
I've used these for simple telemetry and they work well - cheap too. You have to wait a while to receive them through the post though ~ 3 weeks. There are a few UK suppliers.
 
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Dippy

Moderator
For RF there are just so many options it's amazing. Just search this Forum (good luck).
You will get as many opinions as there are RF modules.

The modules range from cheap'n'cheerful , to OTT and , in between are; pricier but better (and, quite often, legal :) ).
In this app I would suggest; keep it simple but not super-cheapo.
It has to be reliable and stable in all weathers.

You also need to consider the Real World design.
Just as an example:-
1. Don't just use a simple Carrier on-off as your switch - your neighbour's similar design (or keyfob) may trigger yours.
So, a little digital magic is required. Dead simple and could save your pyjamas getting dirty.
2. Don't design your transmitting end to transmit continuously when triggered. Make it a 'burst' of data. Again dead simple.
Note that continuous carrier is illegal in UK and could really pee-off the neighbours - as well as being inefficient and 'novice'.

I would be tempted to do bench tests with wires while you are deciding on your RF Modules.

And before Micro digital was as good as now I had impressive results from Old Faithful Holtek HT12E and HT12D plus Radiometrix/RF Solutions modules. They were really good and did most of the hard work for you. But, sorry, would offend the Ch Ch brigade.

A lot of this depends on your budget (??) and how much you value your property, peace-of-mind and soiled jim-jams.
And some relies on your ability. E.g. there are some teeny chip modules out there (e.g. CC1101), but almost impossible for a newby.
Remember: it doesn't matter if Little Johnny's weather station data link fails, but a security system needs to be very reliable and trustworthy.

It makes cable quite attractive... but not so much fun :)
 
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srnet

Senior Member
There is still a requirement for power at your remote devices.

You might be able to arrange it so that say a door switch turns on the power (batteries) when opened, and then transmits, but it does depend on what sensors you had in mind.
 
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geoff07

Senior Member
I built such a thing for a friend to protect his shed (cum recording studio). We buried some cat6 in a duct, with the result that he can have a phone extension as well as the alarm, and to power the alarm as well, and no dependencies on remote resources. Radio is certainly more fun but it isn't particularly reliable, in comparison, due to lots of other uses (try looking at the local 433MHz band with a spectrum analyzer).
 
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RustyH

Senior Member
Thank you for all the comment on, really helped with getting some brain storming going.

I completely agree that a wired system would be easier to maintain, but I don’t think running wires everywhere is going to be practical. So if there is a wireless system that is mid-priced, reliable, and a good option then I would want to roll with that.

There are a few area's I would like to protect, so each would have a different sensing design.

Firstly, the back fence. I was thinking of either a break beam, or more simply a piece of fishing line attached to a switch / vibration sensor. The reason I can’t simply use something like ultrasonic, or motion sensing is cause cats are forever going across the fence line. So I could you the break beam or trip line in a position that would not be effected by cats, but would be activated if someone jumped over.

Next, I have some reasonably high priced garden furniture, that would be a pain to simply chain down. So I was thinking maybe a set of motion / vibration / tilt sensors. That would trigger if the device was moved.

Then there is the front gate (which leads to the back of my house. I could use a PIR, but I think cats ect will set this off during the night. So again, maybe a break beam or something (I could actually set this one up wired though as it close to the house)

There are a few others that are similar to the above.

But the biggest challenge would be the Koi!!! If I could protect them from theft somehow that would be great!!
 
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SAborn

Senior Member
sounds like a big angry dog would cover all areas including the cats, and the bonus is they are wireless.
 
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Dippy

Moderator
RustyH: if you have items within a perimeter then wouldn't perimeter sensing be adequate?
This would be cheaper than per-item protection - and it would give an extra minute or two time extra to notify you.

Maybe if you had break-beam (disguised) on a post about a metre within the perimeter then any animal jumping from fence would be ignored but some great tea-leaf walking down would trigger it.
PIR would be unreliable for many reasons including the critter problem - especially as it becomes more sensitive in colder weather.
For break-beam use a dual or wide beam so that little animals (or snow-flakes :) ) don't trigger it.

Many years ago (reminiscing) I designed a sytem which used a single infra-red Tx/Rx and detected people by bouncing the IR off them. Worked a treat but range limited to about 5metres, but could also be used with a reflector for larger ranges.
It wasn't an easy build but maybe you could investigate a similar technique.

You mention a "wireless sytem"; as alluded to before, there are a million varieties.
Did you want suggestions? You will get a million opinions ;)
What is your skill level in terms of build?
What is your real budget?

Multi-channel RF would be best as then you can choose the clearest channel/frequency.
But if your area isn't over-saturated then a single-channel may be OK with a little RSSI checking and data processing.

Aside from that, you need to think about power-conservation if using battery devices.

If all that is too tricky then resort to SABorn's big dog :)
 
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SAborn

Senior Member
If all that is too tricky then resort to SABorn's big dog
Click to expand...
The advantage with my suggestion is, they run on bio fuel, come pre-proggramed, and still work on power outages in all conditions.

Just dont source one from Ebay, out of China, as it is most likely to be counterfeit or flat packed.

More seriously, you are far better running a length of cat5 cable and doing a wired system, any cheap dumb wireless module will drop out and be intermittent in rain and snow, it will simply loose the data link under bad conditions, resulting in no alert or false alarms, which is the worst of all.

I have used many of the dumb modules for data logging 24/7 and there is always data breaks in bad weather.
Now i use the Dorgi transceiver modules and get perfect data 99.99% of the time, although cat5 cable gives me 100% all the time.

Your system is only as good as the power supply driving it, so to do remote stations is a costly option, where it has been said a cat5 cable will power all stations and allow 6 data lines from 6 station.

Spend the time and cost on developing a good detection system and use a simple wired system to link it together would be my advice, or if all else fails get a big dog.
 
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Dippy

Moderator
"...out of China, as it is most likely to be counterfeit or flat packed"
or has rabies or is delivered as frozen steaks :)

Downside; dogfood in UK is more expensive than electricity.
And electronics doesn't poo on the lawn, doesn't require the Vet, doesn't smell, doesn't (have to) go to sleep and doesn't require walkies when you want to watch the telly :( .

Seriously though, if you design the system well then it shouldn't lo(o)se the link. It just requires a little development time. Though, I fully admit, wired is potentially more reliable.(Unless you use some nasty, inappropriate cheapo wire that rots or connectors that corrode.... probably from Ebay).
I'd use radio - so that's obviously a bad choice.... :)
 
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Dippy

Moderator
"Seriously though also, how much is electricity per Kilo ?"
- mmm... a tricky one.
I don't know whether to base it on coal, gas or Winalot.

If we did the calcs based on E=mc2 on a Bonio then that could keep the RF module going for quite a while :)

Audio - there's an idea. A break-beam alarm that swears at the thief!

"no cables, no IR beams, no dog food"
- no hope, no fun :)
 
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rossko57

Senior Member
Dippy said:
Audio - there's an idea. A break-beam alarm that swears at the thief!
Click to expand...
Yup. Is your aim to catch or deter? Advertising detection is usual - beeps, voice announcement, floodlights. But that then makes avoiding false alarms all the more important.

Have you looked at commercial kit spec sheets to see the capabilitys needed for reliability - outdoor grade break beams, PIR etc - to get ideas
http://www.takex.com/quad-c-4634.php
Even a simple tripwire will get wildlife blundering into it
 
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