Block Detection - Optical versus Voltage

[Anonymous]

Ok guys... I have been modeling for WAY to long, and want that perfect prototype railroad. It's a given that I am using DCC now, but have never fully appreciated signaling, etc...

My turnouts are all manual controll (for now,) Peco turnouts. So, I am wanting to begin this block detection and signalling thing without including the turnout position, etc...

My real dilemma is the same as a large club layout in my area. My new N Scale layout is actually too large for me, so I have to watch the budget when moving to new technology.

I want to know more about this optical sensor stuff... Can we use optical sensors and attach them to our BD162 type block units instead of trying to get voltage drop?

It would be great to use the technology to avoid having to modify all of my rolling stock (diesel era, no caboose.) But I cannot find reliable information on why people are choosing optical vs. transponding vs. voltage drop. I do not want to track locomotives, nor do I want to spend a great deal of time and money on each piece of rolling stock.

It seems to me that if each block had three optical sensors hidden in the track bed, you should logically get direction of travel, occupancy, etc.. to feed a signalling system. It also would seem logical that this setup could be connected to the DCC stuff to convince Loco Net that the block is occupied, or level of occupation.

Please give me your feedback and ideas. I see the little sensors everywhere now, but cannot find information on what voltage they use, wiring schematics, how they interact with block detection / signalling systems, etc...

[CP5170]

Since you are using Digitrax, have you contacted them? I would be interested in their opinion as I have not connected my BD162 yet.

Ken

[RhB_HJ]

It's all a matter how you interface the two.

[ndbprr]

I'm on dangerous ground here becasue I am a little behind you in installing working signals but I have thought about it a lot. Cadmium sulfide sensors which can be gotten form several sources that are fairly small can be placed between the ties and under a light source (like a bulb). They will either let current flow or stop it when the light is not present ( car over the sensor). Just put the light and sensor at a slight angle so the open area between cars doesn't allow the light to reach the cell. Idea 2 is to use infrared transistors hidden in trackside structures, piles of ties etc. There are two components. one is a sender and one is a receiver. If you mount the sender with a piece of brass tube over the end it can focus it a little tighter. This is basically the old electonic eye supermarket door. When the beam is broken it sends a signal or breaks the signal used to trigger the signals. I am fairly certain I want the signal circuit to be independent of track power just to keep things simpler and independent. I tried twin t years ago and found it to be a disaster when using PFM sound. Also tried TTL logic circuits somewhat successfully. The circuit in about 9/78 MR is a fairly good one for both single direction and dual direction running.

[Anonymous]

First I seem to recall reading in the Big Book of DCC that you can combine the two systems as the Big Book suggested this method would reduce the cost of detection. I can't advise you on the wiring though. When it comes to getting info beyound the basics of DCC I feel your pain, I really do. There isn't a whole lot out there to help us wannabe electronic geeks, but right now klutz's, out.

My recommendation is to ask your question at the Digitrax forum at Yahoo! Groups, lots of geeks hang out there.

Also check out the free program called "Decoder Pro" it will help you a lot as well - its free and open code so computer geeks are continually tweaking it.

[Anonymous]

Big help from Circuitron...

Ok, it really was just feedback from Steve at Circuitron. Their DT4 comes with 4 optical sensors. He said each sensor triggers an SPDT switch basically. So when the sensor is covered, it opens the switch to ground. It can handle 10 to 18V DC. This opens the possiblity of triggering an attached relay to send the appropriate signal to anything the relay is in line with.

I have a DT4 coming and will play with it and a couple of relays to change the track to DC from DCC. By then setting the locomotives Prototype braking, Digitrax says that when the loco sees analog, it will begin it's braking, but keep it's lights on, etc... (Cross our fingers.)

I am going to build in override switches in case the sensors malfunction, or receive erroneous signal.

It is then theoretical, that a DP162 could be "tricked" into receiving a current draw when the block is occupied (a little electronics and an additional relay, which would signal Loco Net.)

I still need to understand what to "show" the 162, so I will be calling Digitrax in the next day or so. (Unless someone get's enterprising and calls them first.)

The simple relays to cut DCC and apply DC shouldn't be a problem, but my concern is they will AUTOMATICALLY kill the stop block, regardless of operator intention. Not entirely bad, it is actually prototypical on the main. Now, how do we make the yards and industry behave....

Keep talking and thinking. We are on to something here!