Moonlight Serenade...

Charlie,

Great column!

Yes, I too am a night hawk and light spilling from windows or illuminating a street corner or loading platform has always seemed magical to me.  Sure, night time OP's may not be for everyone, maybe not even for anyone but operating the layout in the dark is just plain fun if you ask me.  Heck, why have lighting if the sun is always shining?

You make the use of the blue rope lighting seem pretty casual but I imagine it was more involved than just stringing it up around the room.  Surely there was a bit more to it than that, no?

Sorry for my ignorance.  Can you give me a bit more detail on the function of capacitor C2.  What do you mean by "ringing" in this case and why is 6 inches the maximum input lead length before the "ringing" is present?  What effect would the "ringing" have on the circuit if the capacitor was omitted?

The "wiring closet" is a really good idea, as is the use of header strips for custom plugs.  Compact, simple, and inexpensive.  Some great ideas here.  Thanks for sharing them!

Light is cool

Great ideas, thank you.

I like your power ideas. Fast and easy.

With my Diamond Valley station I've installed some lilght already.

Wolfgang

Ringing...

If I understand correctly the "ringing" would be a result of the regulator reacting with the inductance in the wires coming from the power supply and would result in spikes on the output. But then I may not really be understanding it correctly. The spikes may not make much difference for our application (driving light bulbs) either - but would make a huge difference if we were powering sensitive electronics with this circuit. The spec sheet called for it if the power leads are over 6" so I passed this bit of info along.

The rope light was indeed a very simple installation. I was fortunate to have pre-wired the train room without outlets in the ceiling which were intended for lighting. This avoided having wires running from the floor to ceiling for rope light power.

Charlie

Ringing

Thanks for the explanation Charlie.  I agree that if the power supply was being used in, say a  digital circuit, then the ringing, as you describe it, would be a huge issue.  Perhaps not in the case of a lamp supply.  I'll breadboard the circuit both ways to test the theory.

You mention a spec sheet, I assume you are referring to the datasheet for the LM317T...

There is another great tip for wiring a layout room, switched outlets up high to allow for added plug-in lighting or accessories down the road!

Thanks again!

1.5 Volt regulator circuits

I said I would and so I did.

I breadboarded two variations of Charlies 1.5 Volt regulator circuit.  I powered my circuit with 12.37 volts of DC from a bench power supply I made from an old computer power supply.

Because I was using a DC input voltage I did not need either the bridge rectifier or the capacitor C1, for my circuits.

The only difference between the two circuits was the use of capacitor C2, seen in this closeup of circuit 1.

The next thing is to connect a voltmeter to the outputs and see what we get.

Cool stuf Blue but...

But although using DC means you don't have to have the bridge in place I'd suggest that you should use the bridge anyway. See what happens to the regulator output if you "accidentally" (on purpose) reverse the input voltage polarities.... IF YOU TRY THIS DON'T DO IT WITH 1.5V LAMPS OR LEDS CONNECTED

I did this inadvertantly and it appeared that nearly the entire input voltage was delivered to the outputs. FLASH! &^%#$&^#$^@&%~!!!!!

The bridge keeps you from making this mistake (or at least makes it much harder).

Charlie

OR... HOT STUFF!

Yes, having fun with it.

I see your point regarding the use of the bridge.  Without diode protection, reversed polarity will result in over 11 volts being applied to the lighting circuit.  Polarity is reversed of course but the 1.5V lamps will not care at all, they'll just burn out regardless of polarity.

I found that adding a 1N4007 diode into the positive input line corrected the problem.  I still get 1.3 VDC at the outputs.  When I reverse the polarity I get zero VDC because the diode does not conduct when reverse biased.  So if you need to rectify an AC supply buy a bridge rectifier.  If you just need reverse polarity protection for the circuit, use a correctly biased diode.

Turns out I was mis-remembering though.  My supply is actually outputting 12.37 VDC.

With capacitor C2 in the circuit the regulator outputs a solid 1.3 VDC.  Without C2 "smoothing" the input voltage, the regulator outputs 1.27 VDC.  Not enough to worry about when using the regulator circuit to power lamps,but Likely an issue in a digital circuit.

This is the final circuit.

The diode

Good idea. The diode fixes the problem and is smaller and cheaper than a bridge. Perhaps I used bridges because I had them on hand...

Charlie

Diode VS Bridge

Either one will do the trick and the cost is not that big a deal.  I am not saying it's wrong to use the bridge as polarity protection or that using a diode instead is better, just that there is another way.  Likely your use of the bridge was a case of having one already.  My use of the diode was the same sort of situation.  While I do have a couple of bridge rectifiers on hand, I have a whole handful of 1N4007 diodes in my parts box.

It should be noted again in this discussion that if one is using an AC input voltage such as would be found on the accessory terminals of a power pack, you will want a bridge and the associated capacitor anyway.