Recently switched from an older form of DC digital control to DCC. For track detection, I used one 6 amp diode and sent track power through it. Used an op amp to measure occupancy etc. What is the hot setup for DCC? I have 80 blocks and want to get the info to my computer for signals (and auto short ckt detection) I have a relay for each block which allows me to switch in/out a block when looking for a short. Works great (1.3 sec to isolate any short). I don't want to loose features I had with my old system. My background is EE. Just don't want to reinvent the wheel if there is something good in print. Thanks Jim Gilbert

-- Jim Gilbert (jgilbert@talon.net), April 06, 1999

Answers

With any luck, a slight modification to what you are using may work for you.

DCC is pulse width modulated square wave AC. There are prevailing methods. One uses a current transformer like that used in some switching power supplies. It has the advantage of not introducing any voltage drop through the detector. And it is electrically isolated from the track power.

The other method is similar to what you are using now. It is two diodes side by side to pass AC in both directions. So for starters, you just need to add a diode in parallel but backwards to what you have now.

After that, it depends on your circuit. I could do a lot of guessing, but you sound like you have the capability to take it from here.

Keep in mind that you can buy an assembled block detector for $8.

Some people run their detectors back to their PC where they use commonly available and fairly low cost digital I/O boards. I imagine you know what I'm talking about. Most of the computer programs support these.

Your other alternative is feed the block detectors into something like a DS-54 to send signals back to your computer via Loconet. This eliminates a rats nest going back to one spot - the whole reason I wanted to get into DCC in the first place!

Check out my web page, Wiring for DCC for some other info. My coverage of block detectors and computer control is a little sparce at the moment due to the requests for more basic info. Darn! I like these kind of toys!

http://members.aol.com/wire4dcc/index.htm

-- Allan Gartner (wire4dcc@aol.com), April 06, 1999.

Hi Jim: From another EE

I recently converted my 35 year old Teton Short Line (TSL) to DCC, abandoning the computerized Automatic Cab Control. Like you, I kept a relay in one leg of each block- plus putting a relay in one leg of each booster for ease of short circuit isolation. I haven't patched up the software yet to do this, but the hardware is in place. Took a little razzing from the DCCSIG group for complicating DCC, but after all thats my fun. VBG

The booster outputs and track feeders meet in a strapable matrix for easy re-arranging.

As to detectors, I scrapped my 24 three terminal devices and built up Dick Bronson's four terminal ones that draw operating power from the DCC and output the logic via opto-isolator. About $6 each. I also scrapped the common rail- Some vendors of DCC argue against the value of that, but I came from the avionics world where we don't like Murphy, and I felt it was the thing to do. I share much of the TSL technical stuff at: http://ida.net/biz/tetonsl

-- Wayne Roderick (tetonsl@ida.net), April 07, 1999.

Jim,

R&D time is definitely hard to come by, isn't it?

DCC isn't too high frequency. After all, it goes through all layouts with existing wiring! I never thought about this before, but we certainly don't need to worry about any diode, do we?

For digital I/O boards, start with Keithley-Metrabyte at http://www.keithley.com/ Look up their PIO-96J. They have been making this basic board for years, if not a decade+. It's their highest density, lowest cost per bit board. They have other boards available, too. All of these type of boards are DCC system independent. Needless to say, you don't need DCC at all for these boards. I don't know that Keithley-Metrabyte are the cheapest in making this type of board. But it should be a good place to start. It's definitely a quality product.

In my do-it-yourself section of my web page, I believe some of the people listed offer software that will work with this type of card. Check out Railroad & Co. I understand they have a better package than the veteran WinLok. WinLok is definetely clumbsy to use so I will be looking into it myself in the next couple of months.

The DS-54 is a Digitrax Loconet product. If you are not using feedback, it will work with any DCC system attached to track wiring or a separate booster only driving accessories.

If you want to send position and block occupancy info back to a computer via Loconet (you cannot send this info back through the rails with any DCC system) you will need to be a Digitrax user to use their device for reporting to a computer.

I THINK I could get around this apparent limitation if you want to try. We'll take this offline if you want to attempt this. After we worked it out, we could bring it back on line.

Allan Gartner http://members.aol.com/wire4dcc/index.htm

-- Allan Gartner (wire4dcc@aol.com), April 09, 1999.

Sorry about the goofed URL. You can reach the Teton Short Line at: http://www.ida.net/biz/tetonsl/railroad/index.htm

The page on detectors is at: http://www.ida.net/biz/tetonsl/railroad/detector.htm

For a real quickie on priciples of detection see: http://www.ida.net/biz/tetonsl/railroad/ocupygnl.gif

-- Wayne Roderick (tetonsl@ida.net), April 15, 1999.