Re: Multiple LEDs on FX-DO

Joó Ferenc

Hello KJ,

Thanks. Is your FX-DO for sale?

Now down to the point. I understand all what you said and will look for a solution to operate more than one LEDs on one port, under the condition that I can actually get the decoder ports working!

My problem is that the ports are all messed up by default, as it seems, and I can't get them to work the way I want.

There is, of course, no manual for the FX-DO and it's impossible to figure out what function is assigned to what port.

Now this probably wouldn't normally be a problem but my Quantum Programmer also developed a fault recently and I can't get it to work. Thus I tried manual programming of CVs.

I reset the decoder, I set all the values of all the CVs shown in the Feature to Port Mapping table of Quantum CV Manager to zero, so in theory no lights should be operating. And still I have some lights that are on. Then I try to assign features to a certain port but they are not in the sequence as the pins on the decoder. This is what I could identify so far:

pin2 = port 4
pin3 = port 3
pin5 = port 1
pin6 = port 8
pin9 = port 5,

where the first two pins on each 6-pin connector are GND and 5V+, thus I call pins 3-8 of the first connector as pins 1-6 and pins 3-8 of the second connector as pins 7-12.

So I am trying to figure out for example what port is assigned to pin 4. I have no feature assigned to anywhere and try to set, say, step lights to pin 4. I try all the values from 1 to 12 on CV 115.113.0 and the single light attached to that pin will not be on for any of those values.

This just drives me crazy, I thought I could at least manually figure out what pin corresponds to what port but no such luck...

KJ, do you think you could perhaps see what function output pin on your FX-DO corresponds to what port?

Thank you.

Best regards,

Ferenc Joó
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kjlovesya via <> ezt írta (időpont: 2021. febr. 14., V, 19:48):

Hello Joo,

  Sorry about your name spelling.  I don't know how to type accents on my keyboard.

  I have a new in box Titan FX-DO and just had a quick look.   There is a error on the drawing for the bottom board.  Perhaps Kelly could have a look at this.   Connector P2 is mislabeled "TRUCKS";  when, in fact, only pins 1 and 2 are for the trucks (as are the schematically parallel P1 pins 1 and 2).   Connector P2, pins 3 and 4 are to be connected to the motor (as are the schematically parallel P1, pins 3 and 4).

  That being said, the wires from P1 are labeled correctly.

  If you look at the bottom of the bottom board, you will notice a large black box component with a hole in the middle.   That is a heavy duty, full wave bridge rectifier.   If you understand how a bridge rectifier works you will know that the voltage across the + and - side (output) is track voltage minus 1.4 volts.   In your case you will have 24 V - 1.4 V = 22.6 V total.

  Kelly recommends using an opto-isolator between the lighting and the top board.   This is the safest route as the expensive decoder board is protected.  The input side of an opto- isolator is internally similar to an LED.  You connect one side to plus +5 V and the other is connected to the decoder light port via a current limiting resistor.  The output side of the opto-isolator can then be used as a simple switch.  N.B. the isolated circuit, controlled by the output of the opto-isolator, must have the GND connected to the GND of the controlling circuit (the "-" side of the full wave bridge rectifier - same as the top board P1 - 8 and P2 - 8).

  A note about LEDs in series.   While red LEDs run around 2 volts,  white LED takes about 3 volts to turn on (some actually take 3.1 or 3.2 V to turn on).  Current controls the brightness.   That's why it's absolutely mandatory that a current limiting resistor be included in any LED circuit.   A +5 volt circuit can only drive one (3 Volt) LED.  However, a +22.6 Volt circuit can drive up to seven LEDs; 3 V X 7 = total 21 Volts (which is less than 22.6 Volts leaving room for the current limiting resistor). 

  We must choose our maximum current for the LEDs.    Most electronics engineers recommend a current maximum of 20 mA.  I use varied current depending on the LED function.   Headlights are brighter than ground lights.  For Headlights I might use 15 mA (very bright) while a ground light might only require 2 mA (considerably dimmer).

  Let's do some math.  Please excuse the simplicity, but this is a forum and our audience may not know how to calculate resistance:

e.g.    22.6 V  -  ( X  3 V)  =  1.6 V        We now use Ohm's law to figure out the resistor value for a 2mA circuit.       Volts = Amps X Ohms    or  Ohms = Volts / Amps

    1.6 V = 0.002 Amp X Ohms   or    Ohms = 1.6 V / 0.002      We get 800 Ohms.   If we don't have the exact value resistor we choose a value slightly larger.  We can use 1000 Ohms (1K Ohm, 1/8 Watt) with no problems.   

  If you decide to add more LEDs, you may add a second series circuit in parallel with the above series circuit.   Use the same formulas adjusting for quantity of LEDs in the series circuits.

  I hope this helps.   Let us know if you have any questions (or corrections).

Best regards,

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