Bill Payne and I have been experimenting with logic circuits for trackside signals for use on our Nottawasaga Model Railroad Club (NMRC) and our home layouts.
See the update about the new signals on our club layout (July 2014) at the bottom of the NMRC page.Commercial circuits by IrDot, Logic Rail, Dallee, etc are possible solutions, but we wanted to see if we could make our own and save some money.
On the Internet we discovered a 3-light signal circuit with approach lighting by R. Paisley. Our first task was to test it on an Evaluator board that I own.
We made the circuit cover 5 blocks so we could see what happens when moving the ground wire that represents the detector. The circuit, as shown in his diagram, has a train detected in block 2. Block 2 should then be red, block one should be yellow and block 3 is green. This represents one-way direction of travel, not bi-directional.
The choice now is to photo-etch signal circuit boards, find someone to do it, or use commercial stripboards as are often shown in wiring circuits in the NMRA's Scale Rails magazine. In the latter method one cuts the traces where needed. You can see the layout of the prototype board in the photo below.
As designed, this circuit uses LEDs. However, if the 470 ohm dropping resistors are bypassed, this can be used for 12 volt bulbs.
On the club layout we have a section of single track mainline. This will need to be bi-directional. That calls for a "coincidence" circuit. We haven't found one yet. The LogicRail boards I have been using on my Utopia Northern allow for bi-directional travel. We need to find a solution.
The other task is to develop a detector circuit that doesn't interfere with track current, like the one that Dallee sells. We've found a circuit using opto-isolators and are about to mock it up as soon as we locate all the parts. R. Paisley shows a Transformer-type, DCC only, block occupancy detector using a 555 timer.
Another set of circuits for block detection and signals is outlined in an NMRA clinic by Richard Schumacher. We haven't tried his yet. There's a lot of good information about assembly of the circuits in the articles.
At a Chapter meeting of the Canadian Association of Railway Modellers (CARM), one of our members, Peter Hughes, directed me to the MERG site in Britain. If you're interested in model railroad electronics (and you must be if you've read this far), check out The Model Electronic Railway Group. This may ultimately supply us with the circuits we need to build.
Bill then used a stripboard planning sheet to design a master signal circuit board for the components. The sheet was downloaded from www.kpsec.freeuk.com. This shows where to cut the traces on the horizontal rows. A multimeter is used to confirm the traces are cut. Bill used a drill bit to ream out the holes. I was using an X-Acto knife.
Bill then built a prototype circuit board using a stripboard that he cut apart with a hack saw so we can make three boards from one sheet to save money. He mocked up the set-up so we could demonstrate how the lights change as a train moves from left to right through the blocks. If this were a loop of track, block 5 would be connected back to block 1.
If you have also experimented with any of these circuits or have other sources, please email me from my Contact page. Bill Payne and I would appreciate your input.
During the summer of 2011 I was adding signal detection to four hidden tracks between Underhill South and Underhill North. I was installing signal bridges at both ends to keep track of what was holding or passing through the "tunnel". I ran into some problems with the green indication not turning off. I was taking the power from the original test installation about 20 feet of wire away. The power was coming from the same computer power supply: 12 volts. The new section's track is within the same power booster district from my Lenz system. Bill Hudson, from whom I buy the circuit boards, has been trying to help me through the problem by email. He had modified his circuit for the current transducers (CT) I am using as noted above. He had some interesting observations about what could be causing the problem. His musings include comments about wire sizes and conductive ballast. I have posted his comments on a separate page: signal detection musings.
Bill Payne and I have continued to experiment with the circuits as time allowed to try to eliminate the problem. Bill Hudson continued to guide us by email. In March, 2012 I ordered a DCCOD detector to see if the updated circuit by Bruce Chubb for DCC railroads would solve the problem. We replaced the CT detector we were using in Bill's circuit with the DCCOD. It worked fine for detection but did not eliminate the double aspects.
In 2014 John Houghton took on the project of installing signalling on the loop trackage on our new end modules. He did an amazing job. He added a new twist to the electronics by installing an Arduino computer on the boards along with the occupancy detection and capacitor discharge units. There is a lot more about the project if you go to my Nottawasaga Model Railway page. I repeat John's documentation here for those who wish to jump into it directly. Here's a pdf explaining the signal aspects and the complete technical documentation with all the schematics and Arduino software code for the construction of the electronics for NMRC signalling operations.
The signalling system at the club was up and running for the 2015 train show season.
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Go from "signal-circuit" to scratchbuilding a brass signal bridge.
Build a cheap HO dwarf signal.
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