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Reply to "Proposed Solution to DCS Watchdog in Yard Tracks (DCS-RC WD Gerber Files Added to First Post)"

d213

OK.  I'm 99% confident it will work in this specific application but there are many flag-on-the-fields to make one scratch their head or other body parts.

I pulled the above from an eBay listing and I realize all the sellers are copying the verbiage from another listing etc. etc.

But a TTL micro?  Yeah, there were a few "TTL" micros back in the day but they would burn so much power as to make them  impractical except for maybe some military or esoteric applications.  For example, it appears there's a 220 Ohm resistor on the input opto diode.  So if using a 5V Arduino, and driving the DL213 ~1.2V opto led, that's a (5V-1.2V)/220 Ohm = 17 mA drive current.  Are you kidding me?!  Can an Arduino even source that much current on an output pin?  Well, even if it can, that's just insane...when the output of the module has a 10K pullup resistor which means that if it is indeed mimic'ing (i.e., High input -> High output) the opto input, it can only source, say, 5V/10K Ohms = 0.5 mA.  That kind of current-transfer-ratio doesn't pass the laugh test.  Either that or maybe the jokes on me?

Well, my concern was to insert galvanic isolation between your Arduino and the DCS-RC, and you get that so it is what it is. 

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  • d213

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