ronwer

OK, thanks for your advice! Ronald

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

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?

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/50 But 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???

Hi, See what you mean. The signal could be used to drive a simple 4-digit counter (74c926) I found some place. But it's still a bit complicated. I need to find a good solution for the sensors that start and stop the counter. Accuracy is not a first concern, the osciallator could also be a 555 I adjust in such a way that the result is aceptable. It's the hopefully big difference between normal objects and the neodymium magnet that do the trick. Anyway, thanks for you help. Ronald

Hello, I have not been succesful finding an appropriate schematics for a small science project I want to built. It's actually very simple: I want to measure the drop time of different objects through a metallic tube (copper). The objects will vary from a stone, an ordinary magnet to the strongest possible neodymium magnet. At the top and end of the tube I want to mount IR-detectors that will respectively start and stop the counter, which result should be shown on a (old-fashioned) LED-display. I want to use as much as is possible old stuff I have lying around, or cheap CMOS IC's. An ordinary stopwatch as I found on this site isn't fast enough, but anything which comes close to one of these two schematics would be wonderful. Any help is appreciated! Ronald Werner Norway