Spark Simulation - Part 2

For those interested, I'm guessing "Part 1" of the topic might be this thread:

https://ogrforum.ogaugerr.com/t...rk-simulation?page=1

As for comments to your diagram:

1. I think you mean 1N4007 Diode (not 1N1007).  However, you don't need the 1000V version of this diode.  1N4003 (200V) or 1N4004 (400V) have sufficient reverse voltage capability for O-gauge applications.  All the 1N400x diodes are the same price and size but if you got a good deal on the 1N4007 or have them already then you're good to go.

2. I suggest you add the graphic showing the polarity of the 3mm LED with the flat-side being the (-).  This would be like how you showed polarity on the diode with the band on the (-) side.

3. Are you sure about the 4.6Vdc @ 20mA spec for the Blue LED?  That seems a bit high; I'd think something closer to 3.5Vdc...but if you found a Blue LED with these specs that works well with your circuit, I suggest you give a part number or source.

4. By using a diode to rectify or convert the AC track voltage to pulsed DC, it can be confusing to analyze how much current is flowing through the LED.  If you have a voltmeter, simply measure the DC voltage across the R1 1000 ohm resistor.  That is, current = voltage / resistance.  So with the isolated rail powered via the axle, if you measure 10V DC across the 1000 ohm resistor, then the average current flowing into the LED is 10V / 1000 ohms = 0.01 Amps or 10 mA.  I'm surprised you get 20 mA average LED current (I'd expect lower) into the LED with R1=1000 and a single diode for AC-to-DC conversion, but so be it.

Thanks for your comments Stan. I will check the D1 Diode selection as you suggest. For the resistor value I used

R=(Vin - Vout)/ 20mA = 17.4/0.020=870 Ohms which I rounded up to 1000 Ohms.

The spec for the LED I have is 4.6V @ 30mA max, but I think less current through the LED will resolve the short LED life experienced in Part 1.

Since you apparently built this circuit, measure the DC voltage across the 1000 ohm resistor and the DC voltage across the blue LED.  The measurements may surprise you!

Stan2004,

I significantly revised the 1st post above taking heed of your suggestions. Thanks again for your help.

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The sketch in this post is the installation technique I use to install spark simulators on the Flushing IRT El on my layout. I spaced the simulators about 3 feet apart where they can be enjoyed by onlookers. The visual effect of the park simulators is dramatic eye candy, and using track power to illuminate the simulators has no apparent effect on the MTH DCS and PS2 trains operating on my El.

My El has MTH Real Trax, so hiding the circuit below the roadbed is easily done. However, for those using track with open ties, it will take a little effort to disguise the spark simulator circuit components. If I had to disguise the circuit, I would use track-side equipment boxes.

In closing, the spark simulation circuit is simple and very inexpensive to build. The spark effects are very dramatic and realistic. This is a great beginner electronics project. Try it! You will be impressed.

Gunrunnerjohn,

The spark simulator would be an excellent product for you to produce for the retail market. The El and subway, and the electric commuter train folks are a significant base for sparks.