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Cheap train detection for hidden staging. Ya'll critique my plan.
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[quote]QUOTE: <i>Originally posted by ereimer</i> <br /><br />i don't know why , but i have the feeling this shouldn't be hooked up to track power to run it . it's going to take someone with electronics knowledge to figure out why i'm right . where's randy ? [:)] <br /> <br />this is just a hunch , i could very well be completely wrong . other than that it looks like a good plan <br />[/quote] <br />Ereimer, <br />Strictly speaking you are correct. As an electronics engineer I would much prefer to see this powered separately. However, that would add to the cost, but in reality a simple DC output "wall wart" type plug pack can be quite cheap from an electronics surplus type store. However I would almost put money on the fact that everybody has at least one of these things lying around the house which is no longer used. <br /> <br />My reservation is that the reverse breakdown voltage of the LED may be less than the voltage coming from the DCS100. When a LED conducts it is said to be forward biased, and the voltage drop across the LED is the forward voltage. Usually somewhere from 1.6 to 3 volts depending on the colour and semiconductor material of the LED. <br /> <br />When the rail goes to the opposite polarity, as it does in DCC, then the LED will be reverse biased and will turn off. Thats not the problem. I dont have any data to knwo what the reverse breakdown voltage is, but here is the rub. If the voltage across the LED exceeds the reverse breakdown then the diode will again being to conduct - but not outputting any light this time. But as we have the resistor in series with the LED in the first place to liit the forward current the same will happen under reverse breakdown and the current wont be so high as to upset the DCC system. <br /> <br />So a separate DC supply would be best. But if the OP uses this design it may work but the LED life may be compromised, or they may be destroyed first time out! I am not sure until I get back to the office and dig out some data sheets. <br /> <br />John
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