ronwer Posted May 22, 2006 Report Share Posted May 22, 2006 I posted a query about a miilisecond timer a couple of weeks ago. Got some useful responses, but are not sure I will be able to realize the project.One of my current problems is the matching of an IR-phototransistor and IR-photodiode.In the following schematics a LD274 is coupled to a BPW40:http://www.circuitsonline.nl/circuits/view/50But I found out that the LD274 emits at 950 nm while the BPW40 has its optimum at 760 nm. (info from www.segor.de)Can anybody advice me if this is indeed a mismatch and what should I use??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 23, 2006 Report Share Posted May 23, 2006 You have a visible light phototransistor in a clear case. It operates at 50% with IR from your IR emitter. You should use an IR phototransistor that usually are in a black case which is a filter for visible light. Quote Link to comment Share on other sites More sharing options...
ronwer Posted May 23, 2006 Author Report Share Posted May 23, 2006 Thanks for your advice. I was already very suspicious about these figures.Would you on the other hand say that it would be possible to use the BPW40 together with a laserdiode, without burning out the phototransistor?I mean, the BPW40 and laserdiode would be used for generating the start-stop signal for my project, and the BPW would be activated all the time, and only when a falling object would pass the beam, there wouldn't be any light on the phototransitor.Would that burn out the BPW40? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 23, 2006 Report Share Posted May 23, 2006 I don't know how much power and what is the distance of your laserdiode.I also don't know how much laser energy would burn your BPW40.It is a visible light system that works only at night in the dark! Unless the range is very short and the phototransistor is shaded very well. Quote Link to comment Share on other sites More sharing options...
ronwer Posted May 23, 2006 Author Report Share Posted May 23, 2006 The distance would be short: about 18-20 mm!But the way they are mounted, would ensure that daylight can not be a problem.For my project to be reliable I somehow believe that a very narrow beam of laser light would be decisive. That way I could get an extremely accurate start/stop-signal for the timer.I want to achieve millisecond accuracy, and diffuse light beams don't give me a good feeling.Any advice is welcome.Greetings from Norway,Ronald Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 24, 2006 Report Share Posted May 24, 2006 The distamce is so short that even the IR diode with the visible light phototransistor will work fine. Quote Link to comment Share on other sites More sharing options...
ronwer Posted May 28, 2006 Author Report Share Posted May 28, 2006 OK, thanks for your advice!Ronald Quote Link to comment Share on other sites More sharing options...
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