Forums

Red laser detector

Started by Chris March 25, 2016
Hi all,

The Chinese are knocking out lasers like these at ridiculously cheap 
prices currenty:

http://tinyurl.com/z59lk8s

And I've seen others *even* cheaper than that including postage.

There are a good many applications for these parts that spring to mind, 
but the ones I'm thinking about require some sort of sensor capable of 
detecting if the beam is broken. I'm not sure what would fit the bill for 
this purpose. Light dependent resistors, even if they work well at this 
single wavelength (typically 650nm IIRC) are probably too sluggish to 
react and useless for all but the most elementary of applications. I'd 
like to make something up to measure the RPM of rotating machinery and 
need something that will provide a speedier and better-defined response. 
Any ideas for a suitable component?

Chris wrote:

> Hi all, > > The Chinese are knocking out lasers like these at ridiculously cheap > prices currenty: > > http://tinyurl.com/z59lk8s > > And I've seen others *even* cheaper than that including postage. > > There are a good many applications for these parts that spring to mind, > but the ones I'm thinking about require some sort of sensor capable of > detecting if the beam is broken. I'm not sure what would fit the bill for > this purpose. Light dependent resistors, even if they work well at this > single wavelength (typically 650nm IIRC) are probably too sluggish to > react and useless for all but the most elementary of applications. I'd > like to make something up to measure the RPM of rotating machinery and > need something that will provide a speedier and better-defined response. > Any ideas for a suitable component?
A silicon photodiode, reverse-biased, should work fine. For a tach application, just a couple Volts of reverse bias should give fine performance. Jon
On Fri, 25 Mar 2016 20:21:31 -0000 (UTC), Chris <cbx@noreply.com>
wrote:

>Hi all, > >The Chinese are knocking out lasers like these at ridiculously cheap >prices currenty: > >http://tinyurl.com/z59lk8s > >And I've seen others *even* cheaper than that including postage. > >There are a good many applications for these parts that spring to mind, >but the ones I'm thinking about require some sort of sensor capable of >detecting if the beam is broken. I'm not sure what would fit the bill for >this purpose. Light dependent resistors, even if they work well at this >single wavelength (typically 650nm IIRC) are probably too sluggish to >react and useless for all but the most elementary of applications. I'd >like to make something up to measure the RPM of rotating machinery and >need something that will provide a speedier and better-defined response. >Any ideas for a suitable component?
Overpriced! http://tinyurl.com/zu6bfuv Photodiodes: Osram SFH2xx. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
>Hi all, > >The Chinese are knocking out lasers like these at ridiculously cheap >prices currenty: > >http://tinyurl.com/z59lk8s > >And I've seen others *even* cheaper than that including postage. > >There are a good many applications for these parts that spring to mind, >but the ones I'm thinking about require some sort of sensor capable of >detecting if the beam is broken. I'm not sure what would fit the bill for >this purpose. Light dependent resistors, even if they work well at this >single wavelength (typically 650nm IIRC) are probably too sluggish to >react and useless for all but the most elementary of applications. I'd >like to make something up to measure the RPM of rotating machinery and >need something that will provide a speedier and better-defined response. >Any ideas for a suitable component?
Red LEDs make quite respectable photodiodes, as long as you don't need super-fast modulation.

"Chris" <cbx@noreply.com> wrote in message 
news:nd46kb$9ll$1@dont-email.me...
> Hi all, > > The Chinese are knocking out lasers like these at ridiculously cheap > prices currenty: > > http://tinyurl.com/z59lk8s > > And I've seen others *even* cheaper than that including postage. > > There are a good many applications for these parts that spring to mind, > but the ones I'm thinking about require some sort of sensor capable of > detecting if the beam is broken. I'm not sure what would fit the bill for > this purpose. Light dependent resistors, even if they work well at this > single wavelength (typically 650nm IIRC) are probably too sluggish to > react
LDRs are pretty slow, and the cadmium in them is too toxic to sit well with RoHS, some suppliers have dropped them altogether - I ordered a couple of packs from China while I still could. Photo diodes suggested by others are probably best, they're certainly fast enough. Photo transistors are more sensitive, but not as fast as PDs.
On Friday, March 25, 2016 at 4:24:48 PM UTC-4, Chris wrote:
> Hi all, >
I'd
> like to make something up to measure the RPM of rotating machinery and > need something that will provide a speedier and better-defined response. > Any ideas for a suitable component?
For just one................. eBay item number: 252230277757 Dan
eBay also has laser "collimating/focusing" lens.  How would these be used?
On Friday, March 25, 2016 at 4:36:59 PM UTC-5, John Larkin wrote:
> On Fri, 25 Mar 2016 20:21:31 -0000 (UTC), Chris <cbx@noreply.com> > wrote: > > >Hi all, > > > >The Chinese are knocking out lasers like these at ridiculously cheap > >prices currenty: > > > >http://tinyurl.com/z59lk8s > > > >And I've seen others *even* cheaper than that including postage. > > > >There are a good many applications for these parts that spring to mind, > >but the ones I'm thinking about require some sort of sensor capable of > >detecting if the beam is broken. I'm not sure what would fit the bill for > >this purpose. Light dependent resistors, even if they work well at this > >single wavelength (typically 650nm IIRC) are probably too sluggish to > >react and useless for all but the most elementary of applications. I'd > >like to make something up to measure the RPM of rotating machinery and > >need something that will provide a speedier and better-defined response. > >Any ideas for a suitable component? > > > Overpriced! > > http://tinyurl.com/zu6bfuv > > > Photodiodes: Osram SFH2xx. > > > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
At 22 cents each, I wonder how they would last ? Andy
On Fri, 25 Mar 2016 20:46:27 -0400, Bob Engelhardt wrote:

> eBay also has laser "collimating/focusing" lens. How would these be > used?
Some of these diodes *need* such a lens, because their raw output is ridiculously fanned out, so some form of correction is required. I'm not quite sure of the technical term for it, but it needs to be a lens (or for best results 3 lenses in combination with each other) which focus primarily in one plane.
On 3/25/2016 8:14 PM, Andy K wrote:
> On Friday, March 25, 2016 at 4:36:59 PM UTC-5, John Larkin wrote: >> On Fri, 25 Mar 2016 20:21:31 -0000 (UTC), Chris <cbx@noreply.com> >> wrote: >> >>> Hi all, >>> >>> The Chinese are knocking out lasers like these at ridiculously cheap >>> prices currenty: >>> >>> http://tinyurl.com/z59lk8s >>> >>> And I've seen others *even* cheaper than that including postage. >>> >>> There are a good many applications for these parts that spring to mind, >>> but the ones I'm thinking about require some sort of sensor capable of >>> detecting if the beam is broken. I'm not sure what would fit the bill for >>> this purpose. Light dependent resistors, even if they work well at this >>> single wavelength (typically 650nm IIRC) are probably too sluggish to >>> react and useless for all but the most elementary of applications. I'd >>> like to make something up to measure the RPM of rotating machinery and >>> need something that will provide a speedier and better-defined response. >>> Any ideas for a suitable component? >> >> >> Overpriced! >> >> http://tinyurl.com/zu6bfuv >> >> >> Photodiodes: Osram SFH2xx. >> >> >> >> >> -- >> >> John Larkin Highland Technology, Inc >> picosecond timing precision measurement >> >> jlarkin att highlandtechnology dott com >> http://www.highlandtechnology.com > > At 22 cents each, I wonder how they would last ? > > Andy
They claim at least 1000 hours. Count on it.