Laser beam sensor

I have a Photoresistor connected to an Arduino. It is set up so that an alarm sounds when a laser beam is shone on the Photoresistor. As things stand, any light shining on the Photoresistor will trigger the alarm. Is there a circut somewhere that can be used so that the alarm only triggers if a laser beam is used and then if a certain frequency laser is used?

Beam break sensors with lasers look cool in movies.
Common modulated infrared (38kHz) is used in real-world applications, like TV remote controls.
Modulated IR receivers (3-pin receivers) reject ambient light.
Leo..

I am wanting to cover about 30m, would IR work over this range?

Check Banner. I don't think you'll like the prices, though.

abasel:
I am wanting to cover about 30m, would IR work over this range?

Yes.

Leo..

That is what I am looking for then. What is your transmitter make/model. The only ones I seem to be find are all rated under 10m.

abasel:
What is your transmitter make/model.

Home-made board with a C-mos 555 (MIC1557) generating 38kHz, with a 120mA constant current mosfet LED driver stage driving two narrow-beam SFH4544 IR LEDs. One LED will probably do 30meter.
The receiver is a TSSP4038 (not TSOP).
Leo..

abasel:
I have a Photoresistor connected to an Arduino. It is set up so that an alarm sounds when a laser beam is shone on the Photoresistor. As things stand, any light shining on the Photoresistor will trigger the alarm. Is there a circut somewhere that can be used so that the alarm only triggers if a laser beam is used and then if a certain frequency laser is used?

Narrowband optical filter? High-end optics like that are expensive.

Cheaper solution is to modulate the laser beam (like an IR remote) and use a photo-diode receiver
and demodulator. Photo resistors are very slow and will not work with a modulated beam.

Alas I am not quiet at the stage of making my own boards. I found the following which would work 100m/328ft Laser Distance Measuring Sensor Range Finder Module Diastimeter Single & Continuous Measurement|laser distance measurer|distance measurerlaser distance - AliExpress i.e. if the distance changes the alarm can trigger.

Given the price however I am needing some with a bit more experience to confirm that it would be a relatively simple taks to connect it to an arduino i.e. I would not need a driver or some intemediatory decoding board.

Going back to Leo's replies I could give building a board a go but I would need to work of of an existing schematic.

From the link;

2 ma electrical flow: DC2.5-2.8V, standby, measuring 120 ma;

I'd be wary just because I'm not familiar with things that operate in this voltage range. I'd need to see the complete manual before purchase.

Thanks, I have requested the docs ... in the meantime I will keep looking. $50NZ is about my max price that I am prepared to spend for this part.

Hello Abasel,
I read somewhere (probably from Forrest Mims) that an LED
can be used as a light detector. The LED responds best to light
it receives that is close the frequency it can produce. This
sounds like a light filter. Good luck.
Also, remote control devices use an IR sensitive lens in front
of the transmitter/receiver. Maybe that would help you.
It may be that a photocell does not respond quickly enough
to 38 KHz to allow selectivity to be applied to the received
signal.
Herb

Going to try the following :slight_smile:

herbschwarz:
The LED responds best to light
it receives that is close the frequency it can produce.

Only if the LED is in a coloured body that filters the light - photodiodes absorb shorter wavelengths
pretty well, the selectivity is not great. This is why IR photodiodes are often black (a dye that
absorbs visible light and lets IR light through, otherwise the photodiode would respond to
most visible light wavelengths).

LEDs (single color, not white) work fine as photodiodes and are narrow band light detectors, most sensitive to light about 50 nm bluer than the emission maximum.

Detection bandwidth is similar to emission bandwidth, although the package color may reduce sensitivity and bandwidth.

See for example How to Use LEDs to Detect Light | Make:

dougp:
From the link;

2 ma electrical flow: DC2.5-2.8V, standby, measuring 120 ma;

I'd be wary just because I'm not familiar with things that operate in this voltage range. I'd need to see the complete manual before purchase.

Sounds like the forward voltage of an LED to me.

@abasel
Can send you a transmitter/receiver pair if you live in NZ.
But I can’t reply/PM to a guest user.
Leo…