laser/photocell based 'wireless'

[computer]

hi,

I was just wondering if I could send 1 way serial data about 10m 'wirelessly' using a small laserpen style laser and two photocell/photoresistors.

Basically, this would be a fixed setup for testing something between my shed/house, and the small laser would send serial like normal. The two photocells at the other end would have some majik (TM) circuitary so that one would be hit by the laser the other measures ambient light, and can 'subtract' allowing me an accurate reading, which would then be converted back to the standard serial info.

would this work?
computer

 

[Nigel Goodwin]

hi,

I was just wondering if I could send 1 way serial data about 10m 'wirelessly' using a small laserpen style laser and two photocell/photoresistors.

Basically, this would be a fixed setup for testing something between my shed/house, and the small laser would send serial like normal. The two photocells at the other end would have some majik (TM) circuitary so that one would be hit by the laser the other measures ambient light, and can 'subtract' allowing me an accurate reading, which would then be converted back to the standard serial info.

would this work?

No need to use two, just one is all you need, AC couple it and ambient light won't be a problem.

 

[tansis]

Google turns up plenty of circuits, here's one..
http://www.geocities.com/SiliconValley/Lakes/7156/laser.htm

 

[zachtheterrible]

I'm not sure about this (someone else please verify :lol: ), but I think that a photoresistor might have too slow a reaction time. A phototransistor would probably be better.

 

[Nigel Goodwin]

I'm not sure about this (someone else please verify :lol: ), but I think that a photoresistor might have too slow a reaction time. A phototransistor would probably be better.

It depends on your data rate, certainly a photo-transistor would handle higher data rates.

 

[computer]

ok I will look into getting a cheap laser pointer from somewhere and stripping it. hope it goes ok.

I will try a phototransistor rather than photoresistor too...

 

[Nigel Goodwin]

ok I will look into getting a cheap laser pointer from somewhere and stripping it. hope it goes ok.

I will try a phototransistor rather than photoresistor too...

Probably the easiest way, and most effective, would be to use a standard IR receiver IC - three connections, power, ground, and data out.

You would need to use 38KHz modulation of your laser though, and it would need to be IR. A lot easier and cheaper to use an IR LED or two, like a TV remote does!. 10m range is easily possible - more if you use optics to focus the beam.

 

[computer]

maybe - but would it work outside well? I will shade the receiver btw...

 

[Nigel Goodwin]

maybe - but would it work outside well? I will shade the receiver btw...

Yes, IR works fine outside - try your portable TV and remote in the garden, bear in mind this isn't a focused beam - using optics to focus both ends of a link will greatly extend range.

Shading the receiver IC might help, but they are fairly immune to ambient light anyway - but it certainly won't do any harm.

 

[DirtyLude]

When I was playing with this, one of the pages that talked about it mentioned that the on/off reaction time of the laser pen led's was not that good. It limited the overall data rate. I think you would have a hard time modulating it to 38khz, if it's possible at all.

Just put the phototransistor at the end of a tube. if you're worried about sunlight.