infrared trip wire...help?

A

Alex3k

Member
Hey guys

I have asked mannny questions latly however i have another :D

Im planning to add like a infrared trip wire system to my system.

I went to maplins and brought this:
http://www.maplin.co.uk/Module.aspx?ModuleNo=10379

I have also found this:
http://www.reconnsworld.com/ir_ultrasonic_basicirdetectemit.html

Would that work?
I plan to incorporate a 08m chip in (as my school has many) to program it so when the beam is broken another sub system is activated (two servo's to control a webcam)

Can anyone point me in the right direction?
 
S

SAborn

Senior Member
You are in for a lot of hard work as the receiver is not the modulated style and will also detect IR in sunlight.

Its not as simple as shining a IR beam at a receiver and detecting if it is broken, you require to transmit a pulse code and detect if the code is received by the receiver end and if the code is not correct than trigger the alarm etc.

Have a look at the IR detectors / receivers used in the picaxe manuals.
 
H

Haku

Senior Member
Those will work but they're really best suited for short distances in controlled lighting conditions, like inside the old-school mechanical ball driven mice.

Ideally you want a 38khz IR receiver, the kind used in tvs/dvd players/av receivers etc, as shown on page 119 of the second manual, these types of IR receiver aren't usually prone to light inteference like the ones you linked to.

Have a read of this thread for an example circuit & code for making an IR tripwire with an 18x, to get it working on an 08m should be easy: http://www.picaxeforum.co.uk/showthread.php?t=16377
 
D

Dippy

Moderator
cdngunner: It depends what "you people" want to achieve.
A well designed break-beam device is almost totally immune to false triggers.
And/or it can be a tightly controlled 'beam'.
And it can 'see' through windows.
The same cannot be said about a cheapo PIR device.

However, as said by SAB & Haku, if Alex3k uses those components he's asking for problems unless the beam is only used in a dark room with the wind behind it. :)

Unless more specifications/requirements are provided (the typical failing with postings) then it's difficult to give a really detailed respnse.

If, of course, it is a school project then we shouldn't be providing a finished solution on a plate and the OP should be doing the work ... and we'll give some pointers.
 
A

Alex3k

Member
Don't get me wrong i dont want it on a plate that ruins allll the fun however i just need some starting points then i can run with it. So do you think the infrared LED (5mm) and infrared sensor shown below would be better?
http://www.techsupplies.co.uk/epages/Store.sf/sec699c15ae24/?ObjectPath=/Shops/Store.TechSupplies/Products/LED021

http://www.techsupplies.co.uk/epages/Store.sf/sec699c15ae24/?ObjectPath=/Shops/Store.TechSupplies/Products/LED020

The aim is to build like a room/house security system. i was going to have a few infrared beams (im not 100% what their offical name is can someone tell me?) to determine where intruders or other people are in the house and then make a program with the house layout on. when a beam is set it will activate the webcam so it can track the people and show on the program where people are...

Is that any help?

Just let me know what you need to know so i can get started.. ima kinda excited!

Cheers
 
C

cdngunner

Senior Member
Dippy said:
cdngunner: It depends what " people" want to achieve.
.
Click to expand...
Corrected it for you.

Since he didn't say it was a school project, I just assumed he was trying to build a home security system for his own amusement. I am one for not re-inventing the wheel.

Maybe we should crack open the laser can of worms....

" sharks with friggin lasers on their heads...."
 
D

Dippy

Moderator
Yes, that's a better choice.
Do you understand why a modulated beam is better?


Then look into the PWM command and see how you can get the correct modulation frequency.
Do remember that for many sensors like this that a continuous 38kHz is not ideal.
And don't forget that IR can bounce around all over the place so shielding and shrouding is good.
And don't forget that strong ambient light and fluorescent lights etc. can upset things - shielding and shrouding can help with this too.

I suggest you do a rough plan and present it here.

Also, spend 20 minutes searching the Forum.
So much stuff has been presented over the years that it would be a good idea to see what has already been achieved and presented.
 
D

Dippy

Moderator
CDN: IR Break-beam and PIR are two different animals with two different characteristics.
Nothing whatsoever to do with re-inventing the wheel. :confused:
As Alex3K had not specificied the application at that point in time then a PIR may have been slightly not-very-good or utterly useless.

Now that he has described the application we can see that PIR may, in fact, be better. It would certainly be easier/cheaper to install.
If using break-beam, where will you install the sensors and the wires.
But for anything decent avoid cheapo stuff. For a quality setup then source sensors that are pro burglar alarm standard.
 
E

eclectic

Moderator
@Alex.

The RevEd IR transmitter and receiver are
very similar to your TV remote at home.

Here's a couple of experiments that you can try
while you're waiting for delivery:

1. A helper presses the remote
while you move around.
Do you block all the signals
all the time?
Or just in certain places?

2. Make tubes and point the remote,
like a torch, straight at the receiver spot
on the TV.
Does it make much difference?

e
 
M

Minifig666

Senior Member
Cdngunner you might have a good idea there. I've just made a break beam detector to trigger a camera with an LDR, a CD laser diode, a comparator, and a 555 monostable to stop it triggering the camera too many times.

Put a black bit of straw around the LDR about a half inch long and it works brilliantly. You don't realy have to worry about background noise unless there is very bright sunlight.
 
A

Alex3k

Member
suggestions on sheilding/shouding methods?
where should i get "pro" emitters and recievers?

Cheers for your help guys i appreciate it
 
hippy

hippy

Ex-Staff (retired)
eclectic said:
2. Try bogroll tubes as a starter.
Click to expand...
When playing with a Lego Mindstorms IR Tower I didn't have too much joy with bogroll tubes but that may have just been the ones I was using. The same style of tube as used in the core of kitchen roasting foil is however much thicker and smaller diameter so that may be a direction to head in. By all means start with bogroll and see if it works for you.
 
N

N12ck

New Member
Hi, i have built this exact circuit and would be happy to help, I built an infra-red guitar where you strum a beam and hold buttons to create music, the infra-red part is just a trip switch essentially, so what would you like it to do and what's the range you need on it?

and to achieve this, PIC is not needed
 
D

Dippy

Moderator
Sorry, I confused things.
What I meant was; if you decide to move to PIR detection and you want quality then use PIR sensors of a make and type used by professional alarm installers. If you are on a tight budget then you will have to lower your expectations :)

I think you need to get back to some fundamentals here.
And this assumes I have got the story right.
I don't want to dampen your enthusiasm but if you want to know where people are then you may need quite a few break-beams and this will have a problem in terms of wiring.
Example:
A break-beam across a kitchen door. (Let's forget about the wiring hassle).
A person breaks the beam and then unbreaks it.
Has he walked into the kitchen?
Or did he dither by the door and walk back out?

Do we have more beam devices across the room?
More wiring?
More lumps on the wall?
More bog rolls poking out from the wall adding to the decor?

This is why PIR was invented :)
Basically, one device per room.
So now I agree with cdng (obv his c.ball is a powerful model).


Note.
"Is that any help?" - doh!
Alex , as you can see, if you provide the information in the first place then the responses can be better targetted. Otherwise we're into guess-mode and sometimes worse ... pulling-teeth-mode and even worse; blood-from-a-stone-mode ;)
The more info up front the quicker the reply.
 
D

Dippy

Moderator
I haven't got a clue what a 'Haunter' is ? Does it mean 'cheapskate' ? :)

OK, so you make your break-beam either bodged or good.
Where do you position/mount it to 95% guarantee room-occupancy detection?
 
F

fritz42_male

Senior Member
Dippy said:
I haven't got a clue what a 'Haunter' is ? Does it mean 'cheapskate' ? :)

OK, so you make your break-beam either bodged or good.
Where do you position/mount it to 95% guarantee room-occupancy detection?
Click to expand...
Cheeky bugger!

'Haunters' are people used to making good Halloween effects from minimal budgets and are often very adept at using common objects for purposes for which they were not intended. e.g. the PIR light I mentioned in the other post.

Surely the point with a breakbeam is not to check occupancy in a general area but to know when someone has passed through the beam. It's an accurate track of progress. PIRs are notoriously temperamental whilst a breakbeam usually avoids false triggers.
 
D

Dippy

Moderator
I was right then ;)

Tracking progress?
Like I said in Post#16
Example:
A break-beam across a kitchen door. (Let's forget about the wiring hassle).
A person breaks the beam and then unbreaks it.
Has he walked into the kitchen?
Or did he dither by the door and walk back out?

If you included direction sensing then I might almost agree... but on this occasion it doesn't sense direction so I can't :)


So, it isn't an accurate tracking of progress.
If you have (moving) occupancy detection in each room then it is FAR more accurate.
Good PIRs are pretty damned reliable as long as a degree of common sense is used in selection of the device (i.e. No cheapo crap*) and a modicum of experience (i.e. not installed by a twerp).
* precisely why I suggested Pro grade!!!!!!



Question: Do the Big boys use the proposed break-beam method to track?
Answer: No.
Question: Why not?
Answer: Because they've thought about all the scenarios.
 
F

fritz42_male

Senior Member
I'm not completely disagreeing with you as I use PIRs rather than breakbeams at my yearly Halloween party. I just shield them well at the end of a tube the length of which controls the field of view. They have the advantage of only needing one 'side' rather than the transmitter/receiver type thing of a breakbeam.

I was just showing that there were simple breakbeam solutions out there
 
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