I've been busy rewiring Summat since the Nottingham show. One consequence of using a Powercab on the layout is that the Powercab does not respond gracefully to a short circuit, especially with two throttles in operation. So to mitigate all the unseemly unplugging of power, swapping handsets and reassigning of cab numbers some form of protection was in order.
Many moons ago Mike Bolton at MERG sent me one of his prototype BCO1 block cut-out pcbs to test with Dynamis. It didn't work, being unable to respond fast enough for Dynamis' lightning fast response to a short. Because of this and also some non too favourable tests with other proprietory DCC systems MERG have put the project on hold and don't currently produce a kit.
I tested it anyway with the Powercab and it worked
It's now wired in on board 2, between the NCE UTP panel and the track bus. I've also put a seperate feed from the UTP panel direct to the DCC input of the MERG Pulsed Accessory Decoder board so that if I run a loco against an incorrectly set point the BCO1 will cut the track power but I will still be able to change the point via the throttle and remove the short!
Great, but as board 1 track bus is still fed from the track bus on board 2 any short will mean that the 3 way point Accessory Decoder will be dead following a short - I need another BCO1
Thanks again to Mike at MERG who is sending me a programmed chip and Pinkmouse of this parish who is etching me a pcb. Now all I need is the rest of the components and I will have another BCO1 for board 1. This will then have it's own section so not only will I be able to change the 3 way point following a short but a short on board 1 will still leave board 2 operational and vice verca
Unlikely this extra BCO1 will be in place for the Mansfield Show, but to be honest, shorts on the 3 way are rare.
PCB etched (cheers Pinkmouse!) parts are on order so I might have the second board ready for the Mansfield Show
here's a quick pic of #1 in situ under board 2.
The thin red and black wires run to an LED mounted in the layout back panel to give indication when there is a short. All DCC signal connections are now via the white sheathed 2 core flex. The red/black bus and heavy feed wires are the 19vDC bus from the laptop psu.
PCB assembled last night and tested - nothing no power to track at all. A quick email to Mike Bolton at MERG though has revealed that the programming on the PIC might not be compatible with the MkI PCB that I have used, will swap the PIC from the (older) working board tonight to prove. If this is the case it's a quick mod to the new PCB and all should be well and good.
Following a good test with the PIC from the old PCB I cut the track from pin 4 to pin 1 and then soldered a new bridge from pin 4 to pin 8 and hey presto, with the new PIC it all works - I now have a BCO1 for both boards. Just got to rewire board 1 now to take it - job for tomorrow....
Here's a pic of BCO1 #2, thanks again to Mike at MERG and Pinkmouse for the PCB