Break beam with Led indication

Projects General Guidance
1

I am trying to come up with a simple way to make a break beam laser with a remote (~ 20' away) led to indicate when the laser is blocked and when it is not. I have see quite a few solutions for making the break beam portion but the wireless activation of the led is my main issue.

As for functionality all I want is for either a tricolor led or a red and green set of leds to activate or deactivate based on the laser state. It would also be nice for it to have a say 30 second or so timeout where if one led was active over that time period it would auto shut off to save battery.

For the laser portion it looks like I have two options. First is to mount it in the main Arduino component box and use a mirror to reflect the laser back. This would allow a AC/DC power supply if this couldn't be built to have a good run time on batteries but I could see it being hard to keep aligned. The second way is to remotely mount the laser in its own box and give it a dedicated power source. If I could add a motion detector to activate it then I may could get away with batteries. The problem with that is It will need to detect motion say 15' away and I don't know what kind of options I have for that yet. If the whole unit including Arduino could be run on batteries and motion detectors while having a good service life that would be great.

So given that info how would be the best way for me to proceed? My searches for the led issue basically come up with people wanting to activate a led with a remote or over wifi. I haven't found really what im looking for yet.

2

So you want an LED indicator at one end of the 20' beam and an Arduino at the other end? You can only get power to one end, so the other end must be battery powered?

You put a laser & photodiode with the Arduino and an identical photodiode adjacent to the mirror at the other end. The laser beam will spread out enough to illuminate both the mirror and the photodiode.

The laser will be pretty weak over that distance (40' round trip.) You will probably end up having to modulate the beam and then detect that modulation at the receiver. IR remote controls do this all the time so the hardware is available very cheaply.

At the battery-powered end, look at modulating your LED too. A PWM output from an Arduino Pro Mini can be used to make the LED look bright without using a lot of current. Follow Nick Gammon's advice on low power Arduinos and you can probably make a coin battery last a year by only waking up and checking for the laser once per second.

IR motion detectors used in automatic lights and burglar alarms are easily capable of detecting motion at 15'. I've owned cordless ones that run for 6-9 months on 2 AA batteries.

3

You don't need a light beam, you just need light.

Laser + accident is you in court explaining your negligence and losing badly. Someone trips and falls and then the fun ends.

For crying out loud, if you restrict the detector to only getting light from a narrow angle then THAT is your freaking beam!

You can use an IR led and IR detector, it will be invisible and not a hazard waiting to happen.

4

Thanks for the quick replies. I think if I give a little more info on the project it will clear things up. This is for a garage to tell me when my bumper is just past the garage door. So it will be mounted around knee height so there will be no eyes coming into contact with this. I thought the laser would give me the precision of the line whereas a IR led would bleed out more since its covering about a 20' distance. Are you suggesting mounting the IR led in a tube to give the IR detector a smaller target thus fixing the issue?

Ill look up more info on modulating the leds and the low power Arduinos. Battery power just gives me some flexibility because of the outlet locations. Most of them are on the opposite end of the garage and I tend to use them a good bit.

5

An easy way to do this is to use heatshrink tubing over the IR LED (shrink it only over the legs), to create a pipe effect. Otherwise a narrow pipe as available.

The best IR receiver for this job is the TSSP4038 (light barrier). The IR LED should be modulated @ 38kHz.

Make sure the IR receiver is shielded (shaded) from sunlight & the IR LED/emitter.
It is also feasible to just mount a mirror or reflective surface on the opposite side - so you just need circruit/power at one side.

To increase range just pass more current thru the IR LED. TSAL6100 is good for this application. (narrow LED angle = better range)

An example IR LED circuit is here: Constant current infrared LED emitter circuit - AnalysIR Blog
..but any IR emitter transistor circuit should also do. (via search)

In general, reduce the value of the inline resistor until you get the required range range.

If possible design your circuit to activate only when needed.

oh, and make sure to read the data sheets of the IR component used.

6

blkexp98:
Thanks for the quick replies. I think if I give a little more info on the project it will clear things up. This is for a garage to tell me when my bumper is just past the garage door. So it will be mounted around knee height so there will be no eyes coming into contact with this. I thought the laser would give me the precision of the line whereas a IR led would bleed out more since its covering about a 20' distance. Are you suggesting mounting the IR led in a tube to give the IR detector a smaller target thus fixing the issue?

Ill look up more info on modulating the leds and the low power Arduinos. Battery power just gives me some flexibility because of the outlet locations. Most of them are on the opposite end of the garage and I tend to use them a good bit.

Yes. Put a detector well behind an aperture or in one end of a tube and aim it at an IR led or even a red led.

If you have any doubt that a red led puts out IR, look at it with a cheap digital CCD camera like a webcam or your phone. Do you see red or white? CCD sees IR as white. Wire up a detector, resistor and led on 1 breadboard and ir led and resistor on another and see how far away 5V through 220 ohms and an IR led can be seen.

Since you choke the view of the detector, you can have 1 led illuminate many detectors.

However there's better ways to detect a car like with capacitance and ultrasonic backups.
Cap sensing is neat and you can make your own out of most anything conductive.

7

Laser + accident is you in court explaining your negligence and losing badly. Someone trips and falls and then the fun ends

Trip on what ?

This is for a garage to tell me when my bumper is just past the garage door. So it will be mounted around knee height so there will be no eyes coming into contact with this.

If a standard garage door sensor does the same thing, you should be able to use the same technology (light beam/photo sensor) but in a smaller package.

8

raschemmel:
Trip on what ?

If a standard garage door sensor does the same thing, you should be able to use the same technology (light beam/photo sensor) but in a smaller package.

Some people trip on their own feet. Some on balls, some on what they don't see because they are carrying things. That's an accident. A light that can blind an eye in a fraction of a second is not.

I have 5 mW laser modules, dot supposed to be visible at 1000 m though I'm sure the dot is bigger that far away. 5 mW is a small fraction of what a led puts out. My Uno leds are bright enough to hurt my eyes at 2-3 feet and yes I know the inverse square law very well. I also know that a phototransistor conducts even from low light. But try it and see.

Have you ever messed with capacitive sensing? Detect someone at the door without a doorbell?
http://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSense

What is the capacitance of a car at the bumper? My finger is plenty enough to detect.
There's a 3D capsense mouse, you need to be grounded and it's not always 1:1 but it works down to small movements. These don't take many or expensive parts so why not to verify "car"?

Also I like my $1.88 ultrasonic detector. It's good to better than an inch to 13 feet, except for fuzzy things but if you put the sensor in a hall then anything that changes the range detects.

9

Well there were some good ideas here, but I've already ordered a couple of 5mW red laser heads off ebay. I plan on targeting a reverse biased red LED as a beam detector. Mine will only be across a 10' aisle in the basement to light up a dark corner on approach. (one way in and out)

Problems with the current system:

Currently there is a hacked battery operated IMD w/daylight sensor working the lights. But that is a problem in the winter when you've just come in from outside and you and your clothes are still cold.

Also, an adjacent door left open (easier to train a cat then a wife, and neither one will shut that door) can allow daylight to the IMD sensor disabling it, and again, if you just came in, your eyes are not yet cave adjusted, so you need the light.

An IMD draws a considerable current and must be on at all times to adjust to, and then monitor the space.

Improved system:

I am thinking I can pulse the laser at fixed intervals several times a second and detect them via a PC interrupt. Lowering overall power requirements.

Missing pulses will be detected to switch the on the lights and reset the on timer, with too many missing pulses being cause to shutoff the lights and trigger an error LED.

I will also incorporate an aiming switch for adjustments to provide continuous visible laser on.

Only 5 pins. (could do it in 4, but that would take more time to program and I am new at that)

Any opaque object will trigger.

Short enough pulses should not be visible. (or damaging)

Not affected by temperature or ambient light.

Re-triggering for longer activity in the area could still be handled by the existing IMD by diode oring in the new trigger signal. (unless of course the cat left the door open again!)

All timings easily adjustable in code.

Development will be done on an arduino, then the code ported to a tiny85.

Any ideas or comments?

-fab