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Cheap train detection for hidden staging. Ya'll critique my plan.
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All of the various suggestions here will work, but none really any better than any other. I am an electronics engineer, so lets look at the various suggestions that have been made here and elsewhere. <br /> <br />Magnets and reeds - Despite comments to the contrary, reed switches are quite reliable, if they are of good quality and tested before use. They are hermetically sealed so do not suffer from corrosion. Choice of contact materials can be significant, especially at low currents, but as theya re here proposed to drive LED's that is not an issue. Magents are an issue, polar orientation could be an issue with magnetic uncouplers, but I suspect not. Spacing can be an issue and I would suggest that you could look on eBay for some Neodymium or other intense field rare-earth magnets. Small magnet - strong field - keeps the reed switch further from the rolling stock for safer clearances. <br /> <br />Cross track optical - great for a hidden staging of course, but has lots of visible stuff. Beware of the effects of incandescent room lighting or incandescent lights in locos etc. The sensor should have an IR filter in the optical path. Very reliable, low cost. <br /> <br />Vertical optical - about 10 years ago I designed a train detection system for a hidden staging for a friend which used IR, the roof of the staging area was solid, so we mounted tiny reflectors above each sensor point. This kept al the electronics in one place and is still working today. The detection circuitry is a little more complex, but after the initial cost of making PCB's it is still relatively inexpensive. <br /> <br />Magnetic proximity detection - common in many industrial applications - you have a magnetic field which is disturbed by the movement of the target object, fine if you have lots of magnetic material such as steel in the object. Great for garden railways but despite efforts by some it is really unsiotable for use on small scale layouts - too much plastic and aluminium. <br /> <br />RF Field proximity detection - create a sinmple RF oscillator where the field of the resonant circuit encompasses the sapce where the loco will pass. As pretty much anything goes thourhg the earea the frewuerncy will change and detecting this will trigger whatever is behind it. Complex and offers no real advantage but was a cheap alternative in the 50's and 60's before modern semiconductors. <br /> <br />SPACEMOUSE: Your suggestion of using photo-voltaic detectors (for the others: photo voltaic detectorsa generate a small amount of electric current in response to light - basically like the solar cells you see on roofs etc). Good idea if you can find a sensor with sufficient output to be usable at a reasonable price. But I am not sure that you can get enough form them to be usable at light levels that would be unobtrusive. But it is certianly an interesting thought and if you pursue it further I would love to hear the rsults of your experiments. <br /> <br />Rob Paisley has a simple and elegant 8 channel optical detector board available, you can buy just the bare PCB form him. It can use photo-transistors or CdS (Cadmium Selenide) cells. http://home.cogeco.ca/~rpaisley4/8PhotoDetect.html <br /> <br />John
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