As rjpb surmised, the actual application is my model railroad. I have a 25-year-old analog controller for it that works fine. But somewhat to my surprise you need to be a somewhat geeky model railroader to go for signals. I've had the "put a small resistor in-line and measure the voltage across it" strategy mentioned before, but I don't really know how to do that from first principles and have no idea how to discover which parts exist much less are useful.
The other exciting detail here is that I might not want variable-voltage DC across M1; there's an alternate standard where I can use +/-12V to send digital signals. That simplifies one aspect of this (I can send "don't move" across the tracks and still detect block occpancy, where now no voltage implies no current implies no detection). It complicates one aspect (the train can respond to the controller by manipulating its current draw). I can buy a DCC system off-the-shelf, but it's pricey, nice ones are overkill for the layout I have, and it still doesn't do signals.
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Date: 2006-12-15 11:38 am (UTC)The other exciting detail here is that I might not want variable-voltage DC across M1; there's an alternate standard where I can use +/-12V to send digital signals. That simplifies one aspect of this (I can send "don't move" across the tracks and still detect block occpancy, where now no voltage implies no current implies no detection). It complicates one aspect (the train can respond to the controller by manipulating its current draw). I can buy a DCC system off-the-shelf, but it's pricey, nice ones are overkill for the layout I have, and it still doesn't do signals.