Lasers and sticky tape.

I've been bread-boarding a
laser beam interrupt trigger for an electronic flash.

The receiver is a BPW34.
Two problems:
The receiver area is only 4mm x 4mm,
making targeting difficult with wobbly lash-up gear.

And, the chip's legs don't quite hold firmly in the BB.

So, I used a piece of “write-on” sticky tape.
Interesting internal reflection properties!
The tape “glows”, and the target area is now
around 10mm x 10mm.

Tried it at ~ 2 metres from a cheap laser pointer.
A fast moving 3mm wire triggers the flash.

e

Tape was:
http://www.rapidonline.com/Tools-Fasteners-Production-Equipment/Service-Aids/Adhesive-Tapes/Matt-clear-adhesive-tape/60218/kw/34-3184

but I'm sure that there are lots of others.

What WILL they think of next ?
Nice one Ec.

That looks like a Pebble picture to me (we won't be able to tell the difference soon)

So, just to understand what you're saying .... just by putting this tape on top of the sensor your can increase the detecting area from 4x4 to 10x10mm ? So it's internally reflacting the laser light into the sensor? Pretty neat if I've got this right.

Smart idea - makes it much easier to align.

A

@Jeremy.
The "naked" photodiode needs fairly precise alignment,
with at least a portion of the laser dot hitting the 4mm x 4mm square.


I hope that the attached photo's give a better idea.
The "top hat" green LED is the "ready" light,
which only switches on when light is received.

Laser about 12" away, at ~60' above horizontal.

Sorry for the rushed quality. :-(
The second pic is a bit washed out and overexposed.

e

And obv. anything which diffuses (etc.) like mad can be used.
With a red laser maybe even your little finger.

Makes you wonder about those kiddy laser tag games. No need for big Ph-Diode arrays, just increased ph-Di spacing and some diffused/cloudy acrylice sheet plus good coupling should do the job.

eclectic said:

Sorry for the rushed quality. :-(
The second pic is a bit washed out and overexposed.

Click to expand...

Now look back and compare it to half of the other images on here. I can see everything just fine

Dippy said:

And obv. anything which diffuses (etc.) like mad can be used.
With a red laser maybe even your little finger.

Makes you wonder about those kiddy laser tag games. No need for big Ph-Diode arrays, just increased ph-Di spacing and some diffused/cloudy acrylice sheet plus good coupling should do the job.

Click to expand...

@Dippy.

You may not believe this, but, I had to try it!
No sticky tape, just finger.

Can someone else please try to reproduce these results?
I don't believe it myself!

e

PS Can we share the PhD ?

I can believe it.
I've fired laser at all sorts of things and watched them glow.

Place any reasonably powerful light source against your finger and you can see a red glow. My monitor can just about manage it! Reminds me of when I did it years ago for Halloween

"Place any reasonably powerful light source against your finger and you can see a red glow"
- I'd never have noticed that

Hold the laser against your forehead with your eyes closed and you can see a red glow when you fire it off. How does that work?

(Don't do this with a military-type laser...).

Guess

And I'm sure if you hold any "reasonably bright light source" against whatever you'll see whatever glow...

Read up on the properties of light and all associated refractions, reflections, fluorescing etc. and then you'll have all the answers at your fingertips, which will also glow.

next thing you'll be telling me is that you've invented a light guide

Pitch black, lights off, let your eyes get used to the dark, close them, hold a powerful flashgun against the back of your hand, fire it and open eyes immediately and you'll see your skin glow briefly - you'll know why.

This could go on forever.. what else do you want to make glow? And will it impress girls?

I'm back to sticky tape as a diffuser/refractor.
(I can't spare any skin).

I've now managed to get the circuit to trigger

A separate electronic flash, and
A D200 camera.

The mechanical construction looks the hardest bit :-(

Dippy.
"next thing you'll be telling me is that you've invented a light guide "

Thanks for waking my brain up!

I've got a few metres of fibre-optic cable.
Might be worth a play. Hmm?
e

Did you never 'x-ray' your fingers when you were a kid? (Using a torch).

Yes.

Isn't that the same as "Place any reasonably powerful light source against your finger and you can see a red glow" from a few posts ago?