Laser beam detection with a serial port
Ever wanted to make your own laser beam security system. You know the kind they have in the movies, with dozens of lasers and the thief has to limbo through them.
Well, I just made a simple laser beam break detector. My computer can now tell when the beam is broken. The parts I used are:
1. 5.6k resistor
2. photo diode, Digikey part #PDB-V107-ND
3. serial port from my PC
You set the RTS pin of the serial port high. You then use the CTS pin to track the state of the photodiode. When the beam hits the diode, current from RTS will flow into CTS and the CTS pin will show high. When the beam is broken, the diode stops the current flow and the CTS pin goes low. Below is the circuit:
I am not exactly an electronics wizard. A lot of this circuit was from trial and error and from reading Sam's laser FAQ. If anyone sees any problem with the circuit, drop me a note. The C (for linux and probably other unix systems) code I used is here. You have to run this program as root. To compile do gcc relay -o relay.c
To run type ./relay /dev/ttyS0 (or whatever serial port you use)
The photodiode is the biggest I could find, but it is still pretty small. I had thought about running a few lasers around my house, but aiming them correctly would be a pain.
Resources:
Sam's Laser Faq
laser communication system
I want to build a photo detection circuit for a laser communication system. Any help?
Great..¡¡¡¡
This is cool..You could use your proyect to make four more laser detector ...'cause your serial port support more...
ir
this could work with ir for a hidden trip beeam
sweet
sweet
help
I want to build a circuit for a laser detector connected to AVR atmel8535 microcontroller through RS232
can anyone give me an idea?
Is SV5637-001 is the best be a laser?
Is SD5443 phototransistor is the best to be a sensor?
I need suggestion to convert output current from SD5443 to voltage in TTL signal so it can be read by RS232 direct to Port C in atmel 8535
do anyone know how to do it?
-cindy
harhariyanti@yahoo.com.sg
Take a look at this
Take a look at this site:
http://www.electronics-lab.com/projects/pc/002/
It uses a MAX232A to convert to TTL. You could probably do something similiar with your SD5443. As far as lasers go, I just bought a cheap laser pointer. Not sure which laser is best.
good luck
chad
Bicycle detection and rounds counter
Hi all,
Looking at the wiz things you guys make here, I have a little request.
I would like to organise a bicycle race.
Therefore I need a system which detects a Bicycle passing through the finish.
2 criteria :
As there are several bikes in the contest, the system must detect which bike is passing the finish and register the time.
How can I make this at home ?
Best Regards
Danny Surin
Detecting the bike crossing
Detecting the bike crossing is easy. You can use the circuit I made or better yet use the same circuit with a microcontroller to make it portable.
The hard part is telling which bike is crossing. You would probably have to use some sort of RFID tag. Take a look at this project and they may give you some ideas:
http://people.interaction-ivrea.it/c.noessel/RFID/design.html
RFID tags have limited range but they may work for what you want.
thanks
chad
Great
I have to commend you for your C code. It's just the C code I've been looking for.
I've got a similar application of this device. I've built a computer to reside in my car for GPS, ECM Monitoring, MP3's and have the PSU wired directly to the battery. This is all cool until you forget to shut your PC off one day.
I can connect pin 8 to an ACC/IGN switched wire and slighly modify this program to shutdown my computer within 5 minutes of the ACC/IGN wire loosing voltage. Now all I have to do is turn my computer on whenever I hop in the car, and forget about it!
Thanks!
laser Thing
lmao, if you just wanted to get past it, just put urself in a red box of plexiglass or wrap ur self in cellophane! you gotta find a different way of fixing the sensitivity. lol just a hint. l like pi!
Bogus Comment
That doppler effect you hear is the clue going right by you.
Maybe not bigger, but...
A bigger light detector may not give you a bigger response. The laser only makes a small dot, so the areas not hit by the laser would not contribute to a more sensitive reciever. In a pinch, a regular LED can be used as a sensor, and if you use a red LED it should be sensitive to the red spectrum of the laser (assuming you're using a red laser). If the 5.6k is replaced with a 10k, and the sensor replaced with a photo transistor (base not connected, emitter to RTS, collector to CTS) then it could be more sensitive. As has been mentioned by others, putting the photo sensor at the bottom of a black (non reflecting) tube will help directivity and prevent outside light from getting in. Alignment would be accomplished by putting a volt meter across the sensor and adjusting the laser for the lowest voltage reading.
jammit
Bigger detector
I was assuming that he wanted a bigger detector to make aiming easier. :) And of course there's another trick to try to make it less sensitive to extraneous light sources: red plexiglass or cellophane just in front of the sensor.
N
Bigger photodetector idea
My compliments to you for publishing this simple hack.
Did you know you can use a reverse-biased solar cell as a photodiode? If you want a bigger target for the beam, that's a fairly easy way to go.
Be sure to use a single cell, not a "solar battery"... you want a crystalline solar cell, something that produces maybe 0.7 V when BRIGHT light hits it, not much more.
I haven't QA'd your circuit design but I'd wire the solar cell with the (+) side to RTS and the (-) side to your pull-down resistor, and then hide extraneous lighting from it -- you could use any opaque cylinder (think toilet paper roll, or putting the cell in the bottom of a Pringles can; and remember duct tape is your friend...)
One potential "gotcha" is that the max positive voltage from an RS-232 device could be over 20V (though on modern PCs it's usually 12V or less, down to as little as 3V on some palmtop devices). Check the voltage if you have a meter; if it's 12V or less it'll probably work fine.
Another gotcha is that some fancy solar cells taken from solar arrays have built-in "protection" circuitry that will hose things up for this purpose.
As for aiming the beam(s), I could suggest various tricks, but I'm not sure what the problem is. Email me if you wnat to discuss it further... :)
Nort
n . m a x i m u s @ g m a i l . c o m
PS: crystalline solar cells
PS: crystalline solar cells are usually blue-to-black in appearance. The browniish amorphous ones (such as one finds in cheapie solar-powered calculators) are a poor choice for this application, I think.
You could drop $4.50 plus shipping and get two cells by tearing apart one of these, for instance...
http://www.allelectronics.com/cgi-bin/category.cgi?category=565&item=SPL-05&type=store
Cheers,
Nort
cool
cool project
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