I have no indication of DCC track power on my panel. With 3 subdistricts (cicuit breaker or reverser circuit bards) on my system, is power indication as simple as adding 5mm LEDs with 1k ohm resistor to the panel, connected to each subdistrict buss?
Paul
Modeling HO with a transition era UP bent
For best results, you should have a diode bridge rectifier connected to the DCC bus wiring, and take your LED voltage from that. You will still need a 1K Ohm resistor with the LED.
Paul:
You can use an LED as you suggested but it would be better to wire a conventional diode anti-parallel with your LED to protect it from reverse voltage and extend its life. You will also need the 1 K resistor.
Joe
I use NCE EB-1 circuit breakers. They have an LED that is ON when track power is on. There is a place on the board to add another LED at a remote location, so that would give you a track power indication on a control panel if you wanted. PSX breakers also have LED indicators that you can add a remote LED if wanted, but their LED only lights up when there is a short.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
There's a two pin conenction near the input terminals on the PSX and PSX-AR that you can hook an LED up to that indicates power is on.
To roll your own, yes, I'd put an ordinary diode anti-parellel to the LED to keep the reverse voltage down, but it seems plenty of people and plenty of systems just use the LED and resistor, no reverse voltage protection,a nd they still last for years. The miniscule current with a 1K resistor probably helps.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
To add to what Randy has said in his last paragraph, I am in the plenty of people crowd, for years never had a problem. The only times I ever use bridge, or filter circuits, is in use with transistor circuits.
Frank
For the reverse diode feature, do I just wire it, polarity wise, so it prevents bypassing the LED/resistor during LED current flow, but on reversed polarity (where the LED can't pass current) the diode allows current round the LED? Curious what this does wrt LED life??
A similar rating to the diode and resistor? Or, which diode bridge rectifier from Radio Shack (some about $1.50?
http://www.radioshack.com/search/index.jsp?kwCatId=13384949&kw=diode%20bridge%20rectifier&origkw=diode+bridge+rectifier&sr=1
I can't find a diagram via google, except for the fancy diode bridge thingy.
Thanks.
peahrens For the reverse diode feature, do I just wire it, polarity wise, so it prevents bypassing the LED/resistor during LED current flow, but on reversed polarity (where the LED can't pass current) the diode allows current round the LED? Curious what this does wrt LED life?? A similar rating to the diode and resistor? Or, which diode bridge rectifier from Radio Shack (some about $1.50? http://www.radioshack.com/search/index.jsp?kwCatId=13384949&kw=diode%20bridge%20rectifier&origkw=diode+bridge+rectifier&sr=1 I can't find a diagram via google, except for the fancy diode bridge thingy. Thanks.
Your description of anti-parallel diodes is correct. The idea behind using this setup is that in an AC or DCC circuit the polarity is constantly changing and the LED or other diode sees the voltage reversing. The LED (or diode) passes voltage in the forward direction and blocks it in the reverse. However, that reverse voltage can have an adverse effect on the LED. The anti-parallel diode conducts the reverse voltage and spares the LED. Any of the common 1N4XXX series or other low current diode can be used as the anti-parallel diode. If you go with the diode bridge setup any low current bridge of the proper voltage rating will do. I would choose one of the smaller bridges listed by Radio Shack. All of them would work but most are way overkill for the low amp circuit you will be making.
Yes, that is the description of how an antiparallel diode works.
'Regular diodes are usually rated by current and the peak inverse voltage they can stand (PIV). Common values for small diodes like the 1N400x servers are 50 volts, 100 volts, 200 volts, and even 400 volts and higher. That means, if the voltage is applied across the diode (in the direction where the diode is blocking the current), it will be able to withstand voltage up to that level without breaking down and going poof. LED junctions, on the other hand, generally cannot take much more than their forward voltage in the reverse direction - an LED that drops say 2.1V, can;t handle much more than that same 2.1V applied in the reverse direction (where the LED won't light).
Now, if you wire a regualr 1N4001 diode anti-parallel with the LED, when the current is flowing against the LED, it's flowing with the 1N4001. The 1N4001 drops 0.7 volts across it. So the LED sees 0.7 volts in the reverse direction, rather than seeing full track voltage in reverse direction. When the current flows the other way, so that the LED is on, it drops its usual 2.1 volts or so (white LEDs are around 3.5 volts, red are 2.1V or so - but you can get different ones with different characteristics. In a serious complex electronic design, the different parameters actually matter, for our purposes, it's not critical that you get a specific one). So the 1N4001 sees 2.1 volts across it in the reverse direction - which is perfectly fine because a 1N4001 is a 50 PIV diode and can withstand 50 volts backwards. And you can see how this would also work with two LEDs wired anti-parallel, the one not lit because the current was ont he wrong half of the wave would see the 2.1V drop across its partner, which is within the safe range for the LED. Kind of pointless to use 2 LEDs on NCE, since the DCC waveform will always be symmetrical (unless the output drivers blow) and thus the average DC voltage is 0. On systems like Digitrax and Lenz where you can run a non-decoder loco on address 00, using two different color LEDs back to back (or a prepackaged bicolor LED, the type with just 2 wires - inside there are two LEDs wired anti-parallel) makes some bit of sense because as the speed is increased on address 00, the waveform gets either more positive or more negative as far as average DC voltage, thus one or the other LED will be on longer and contribute more to the color mix. A red and green are the most common paired up in a bicolor LED, apply DC one way and you get green, flip it around and you get red. Apply normal symmetrical DCC and you get an orange color. Using address 00, you get either more red and less green, or more green and less red. The track status lights on Digitrax boosters are all bicolor LEDs so you cna see if address 00 is in use and not at stop. Also handy for wiring multiple boosters and making sure they are in phase - select address 00 and turn it all the way up. The LED will be almost all red or almost all green. If all boosters show the same color LED, then all is good. If one is different, then the control bus is likely out of phase to is and you'd get a short when a loco crossed the gaps on the track. For systems without address 00, the easiest way to check this before running a train is to use a bicolor LED and 1K resistor, and put it across a gap. If it lights, the boosters are out of phase. If it does not light, they are in phase and everything is good.
Randy:
Thanks for the info on booster phasing. It is quite logical when you think about it but I never had the occasion to use it.
Thanks, all. I appreciate your efforts to explain this stuff! I still wanted to see a diagram as I was not 100% on what "anti-parallel" meant; i.e., the diode parallel to the LED only or to the LED/resistor combo. Thinking about the need to keep the reverse voltage drop cross the LED small, and reading your explanations, I presumed the diode had to be across the LED only, with the resistor in series with both. That was confirmed with the diagrams in the attached (another google success). The article is about a boat and 120v AC, but the same principles.
http://www.boat-project.com/electro/panellight.htm
I must confess that this old guy just remembered (after looking at the documentation) that the 3 sub-district circuit boards (OG-CB and OB-ARs) have spots for optional on-board or remote LEDs to be added. It looks to me like the board LED spots have resistors in their path so I can just (with some under table soldering) run wires to LEDs at the panel, or save the long runs and do the buss supplied LED/resistor/diode approach for fun and learning.
This hobby has lots of learning curves. Thanks for helping me out.
peahrensI have no indication of DCC track power on my panel. With 3 subdistricts (cicuit breaker or reverser circuit bards) on my system, is power indication as simple as adding 5mm LEDs with 1k ohm resistor to the panel, connected to each subdistrict buss?
i think it really is just that simple to indicate power on a DCC circuit. The image below illustrates what you suggested for a somewhat different purpose. I pretty sure that an LED can tolerate the reverse voltage with a series resistor. The LED brghtness will vary depending on the duty-cycle of the DCC signal. From http://www.brian-lambert.co.uk/DCC%202.html.
greg - Philadelphia & Reading / Reading