diode logic signal control ?

Model Railroader Electronics and DCC
1

working on hidden staging loops that connect to a two track mainline. An auto-reverser is required when the loop connects back to the mainline

because of the AR, the loop polarity it only correct at one end and signals indicate whether it is clear to enter staging from one of the mainline tracks or to exit the loop to the other mainline track.

there are guard blocks with detectors on each side of reversing section boundaries in addition to other blocks indicating the occupancy of a staging block (2 trains / track). An “entrance” block on the mainline to enter the loop and an “exit” block on the loop to the mainline.

the signal should indicate stop if either the entrance or exit block is occupied.

the detectors are active high and have both non-inverting (e.g. EntrDet) and inverting (e.g. EntrDetN). We’re planning on using diode logic to control both a red and green LED at both ends of the loop.

any other suggestions?

there are actually 5 loops connected to 4 mainline tracks. One pair of mainline tracks branches into 3 staging loops and 1 AR and the other pair of mainline tracks branch into 2 staging tracks and a 2nd AR.

we may also need to consider if the particular staging track is occupied and turnouts aligned to it, in which case the entrance signal should be stop. more complicated logic would then be required and it may be easier to just use a inexpensive Nano but interested in using simple diode logic.

2

Looks right, but if you need more complex logic you might want to look at using 4000 series CMOS logic gates(since it looks like everything runs on 12V, not 5V logic levels), if you don’t want to go the micro route. I mean, you COULD build the whole thing on diode logic but too many layers and the diode drops start to get you. For example, you can add an additional set of diodes to make those 3 input gates, but one can;t override the others to make an XOR without instead making another stage which takes the output of this and combines it with the signal from the other detector. Depending on what indications you need, maybe it would work, giving you a red if either end or the middle detector was occupied. Green might be the problem. If you need to add even more inputs - it would definitely be time to go past the diode logic and use either logic ICs or the micro.

Diode logic worked great, until they created RTL and DTL, and then TTL and CMOS. Some of these new guys would say you need an ARM Cortex based microcontroller as a minimum to handle this [(-D]

–Randy