Whats a good, fast, cheap sensor for a laser?

[1mikef]

I am looking for a fast, inexpensive laser sensing component. Any ideas. The cheaper the better.

 

[btrueblood]

A photodiode is pretty cheap.

 

[analogkid2digitalman]

What wavelength, spot size, and power? These all dictate what type of sensor is needed. (i.e. photodiodes may not respond well or at all to IR radiation)

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[1mikef]

Thanks for the reply,

650nm, Spot? .125 spot, and power I am not too sure about. Photodiodes are like 4 bucks each. Thats a little high for me. LDR's can be cheap, but I am concerned about their dissipation rate.

What do you think?
and thanks again.

 

[analogkid2digitalman]

Should be able to get photodiodes for easily under a buck, check Allied or Newark. If I recall, LED's also respond to light, you may want to try experiementing with a RED one.

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[1mikef]

how would I go about finding someone to help me with my circuit? Is there a firm or freelancers that are easy to reach?

 

[analogkid2digitalman]

With specifications and desired operation details, I'm sure many of us here would be glad to point you in the right direction or come up with a solution. Is this a homework assignment?

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[1mikef]

More like a hobby.

I want to be able to determine how long my sensor is blocked. So for starters, I need to know what type of sensor to use. You suggested a photodiode so I will look into that (thanks). Next I need to know how to wire it so that ambient fluctuation does not interfer with my readings. I just want to know if the laser is blocked and for how long.

 

[IRstuff]

What do you want to do with the output? A PIN diode will work in many applications.

TTFN

 

[IRstuff]

Is this a school project?

TTFN

 

[Myndex]

A black housing with a tube leading to the photodiode/xistor will help prevent ambient light from affecting the performance.


A

 

[IRstuff]

What sort of ambient? From experience, most photodetector sensors are like vampires; they hate sunlight.

You can also filter your detector, similar to TV remotes

TTFN

 

[1mikef]

THe output I would like to read on my PC, I will have to have the sensors pigtail to fit my I/O card.

I am planning to use the black housing. THe PIN doiode is a cool idea, I will look into that.

How do I wire up the diode? Is there anything I should consider? I just want to be able to know when it is on or off, and it needs to be pretty fast.

I will probably not respond anymore until later tonight.
Thanks for all the help. and please keep any ideas coming.

 

[analogkid2digitalman]

For speed, you want to reverse bias the photodiode- this reduces the junction capacitance. The diode then generates a current proportional to light intensity (until saturation). You then need a current-to-voltage converter circuit (think high speed op amp). Follow this with a high speed buffer or TTL driver (schmitt?) to interface to the digital input on the I/O card. Suspect that diode responce will be way faster (10's of nsec, depending on photodiode size and capacitance) than your software (10's of msec). Suggest a narrow bandpass filter to only allow your laser wavelength to get through to the detector.

Hamamatsu, a major manufacturer of photodiodes has some good app notes, here are some links to get you rolling:

http://usa.hamamatsu.com/assets/applications/SSD/si_pd_circuit_examples.pdf

http://usa.hamamatsu.com/index.php?id=13196002

Good LucK

-Pete


Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[1mikef]

Thanks for the head start. If you know anyone that would like to draw up the circuit, let me know. It started out as a simple circuit, (it probably still is), but I am sure I will need help. The schematics you linked me to will be very helpful.

Thanks
Mike

 

[nbucska]

The best way to reject the ambient is to modulate the light source with a -- relative high -- frequency and
use selective amplifier. Radio Schack had a 40kHz
receiver module years ago.


<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032