Picture this! I am using a 12VDC regulated power supply with PRR position light signal. When I touch a green, yellow & a black to ground of the power supply from the signal with no resistors attached to each of these 3 leads & a brown with a 1K resistor to the +12V side each aspect lights up. What i`d like to know is :
1. Is it possible to tell whether this signal is cathode common or is it anode common?
2. Why is there a resistor in the common lead?
When I use a 5 volt supply and do the above I get nothing to light up. I wanted to use 5 VDC because I use current sourcing on a CMRI system & the output of each aspect is 5VDC max. I am thinking the signal leds are wired in series with the center led wired in series with the common & that this congiguration eats up all the output voltage.
Thanks
Bob D
Bob D As long as you surface as many times as you dive you`ll be alive to read these posts.
Well, if the common is on the power supply + that makes it common anode.
Are the newer CMRI boards different? I happened to just go through the original articles from 1984 and the output cards were all open collector current sinks, which is exactly what you want for signals like this.
DO you know what make thses are? Allt he ones I cna find have the center LED wired seperately, you normally need a few steering diodes to make the center light up when it is supposed to. They typically have about 5 wires coming out - a common, 3 aspects, plus the middle. Other have 6 wires - common, center led, and 4 aspects. One of the ones I found, from Oregon Rail Supply, has the diode board available as an add on product, connect the signal to the diode board, and connect the signal controller to the other side of the diode board.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
subman When I use a 5 volt supply and do the above I get nothing to light up. I wanted to use 5 VDC because I use current sourcing on a CMRI system & the output of each aspect is 5VDC max. I am thinking the signal leds are wired in series with the center led wired in series with the common & that this congiguration eats up all the output voltage.
As Randy said, the signal is wired common anode.
First, check one set of lights at a time. How many LEDs light up with just the green and brown wires? If three LEDs light up in the vertical direction, you may not need steering diodes. If the center LED does not light up, then you may need the steering diodes.
Second, how do the CMRI instructions show the signal hook up? Does the CMRI system have resistors already installed? If not, you will need to use them as required. For 5 volts, the resistor can be as low as 100 ohms. 200 ohms might be a safer value. The resistor can be in either line or wire. If you do not use a resistor in the common wire, you must have a resistor in each of the other wires.
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.
From my experience NJ Int and Tomar signals are usually wired for 'Common Anode' - Atlas and ISS signals are usually wired for Common Cathode'.
Using a 'common' side dropping resistor is bad practice for several reasons. Resistors are cheap and a separate resistor for each lead is better. The 'load' varies as you add/remove devices, so the actual resistor value can change. A 5 Volt DC power supply is cheap and a better solution.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Using a 'common side dropping resistor' per signal is OK. One resistor per power supply is not a good idea due to load changes.
Thanks guys I just heard from the person I bought the signals from and he confirmed what you all said that they were common anode which shocked me because Intergrated Signal Systems uses common cathode for their signals. I know because I bought 14 signals from him and his boards are set up for common cathode. The seller told me that he had ISS make these up common anode so he could use current sinking on his CMRI boards.. Randy yes CMRI does have a board that accepts 24inputs and has 48output pins on it using current sourcing of +5VDC and these boards are used for common cathode signals. The cost of this board assembled is $200.
Yeah that's not the board you want for these signals, you want the more simple open collector outputs (current sink). Seems to be one of the tougher things for people to get their heads around with DCC decoders - the common is positive, the function 'outputs' are all open collector current sinks. It's much more efficient that way.
That's the only problem I have with CMRI, it's quite expensive unless you just buy bare boards and find parts yourself cheap. Since each signal needs 3 lines, that 48 output lines operates 16 signal heads. The $100 SE8C from Digitrax operates 32 signal heads. Dick Bronson's Tower Controller is $115 for the same 64 total IO lines as the SMINI. Of course, these options mean you need Loconet, but that does not mean you need to use Digitrax DCC. To implement Loconet, all you need is one of Dick Bronson's Locobuffer-USB interfaces. No Digitrax command station needed. Elmer here I belive is one who does that, he uses NCE DCC to run the trains, Loconet for the detection and signalling.