[Gordon H]

QUOTE (ebaykal @ 27 Aug 2008, 15:29) <{POST_SNAPBACK}>No hassel of soldering, no resistors, no diodes, no CDU units, just a simple switch and you control your solenoid motors easily. AC,DC or DCC whatever the source, it works.
Actually, it is a CDU in itself.
This was a concept I pioneered in MERG some 14 years ago with a kit known as the PMD1. Remarkably similar, going by the pictures, though I must admit it hadn't occurred to me that you could drive a couple of LEDs to indicate which way it was set. My take on this was that the switch position would show you this information. The main thing (as with Richard's) is that you can use a simple on/off low current switch for control, with all the high current being dealt with locally to the point motor itself.
More recent versions of the MERG kit include the option of an on-board 8A rated DPDT relay as well (so suitable for DCC frog poarity switching etc). However, as with all kits you do have to put it together yourself.

 

[Gordon H]

QUOTE (Richard Johnson @ 31 Aug 2008, 10:42) <{POST_SNAPBACK}>The interface is an opto-isolation board so when that is used you can use any form of triggering from any decoder of any brand - the Opto board also has bridge recitifers built in so whether the ouput of the decoder is common +, common - or ac the MASTERswitch doesn't care.
Can I ask why you chose to use an additional bridge rectifier instead of adopting a simple AC input optocoupler to achieve the same effect?
Can't say what the price might be in Australia, but the KB814 AC input opto is only 14p from Rapid Electronics.

 

[Gordon H]

QUOTE (Richard Johnson @ 3 Sep 2008, 03:08) <{POST_SNAPBACK}>***Why we made circuit design decisions is not really the sort of discussion for a forum.
Why not? If pictures are presented to a forum showing what an item looks like, surely they are just as likely to prompt questions as anything else.
After all, you wouldn't expect people to refrain from asking why Hornby etc. had chosen to do something in a particular way when presented with a picture of one of their items. That is what these forums are all about.

QUOTE However, to clarify a little for you. In fact there are 2x bridge rectifiers on the opto board, not one.
Isn't that simply because it is a dual board? Unfortunately I can't see the picture where I am at present because Photobucket is restricted here, so I am working from memory.

QUOTE The opto board is an added project we really didn't originally intend however we produced it as it was clear that there were some possible applications that might compromise reliability and that was completely unacceptabe to us, so it is made perhaps heavier than needed but it is bulletproof.
Not doubting that, but unless I have completely misunderstood the intention of the design, the rectified control signal still has to pass through the opto LED, so I can't see how that is any more bulletproof than my suggestion, which if feasible would have reduced your component count and board size (and therefore cost) by moving the rectification function into the opto itself.

QUOTE Cost isn't an issue: Our component pricing is nothing even similar to retailers such as Rapid. Durability is.
Cost is ALWAYS an issue. However, from experience I can believe that the component cost has little bearing on the eventual retail price. That is common throughout the commercial world.

QUOTE The Opto boards are now provided totally free of charge where clients specify at the time of purchase that they will DCC control the MS.
Fair enough, you are bearing the cost - which seems even more reason to adopt the simplest possible arrangement available.

Sorry if this all seems a bit critical, but my interest in such matters tends to dominate the thinking. Dealing with this sort of circuitry on a daily basis myself, as I do, automatically prompts questions no matter how hard I try not to get involved!