Lighthouse Circuit

[kcflyer]

I notice that there is also a current path backward though three 10k resistors to the base of the adjacent transistor. Will that current be too small to trigger it?

 

[Nigel Goodwin]

I notice that there is also a current path backward though three 10k resistors to the base of the adjacent transistor. Will that current be too small to trigger it?

There is no such path, the path is via two resistors to the output pin of the chip, which will be low - preventing any path through the third resistor.

 

[Roff]

I notice that there is also a current path backward though three 10k resistors to the base of the adjacent transistor. Will that current be too small to trigger it?

Keep in mind that, if Out0 is high, ALL the other outputs are low. Out0 current cannot get past Out1. Furthermore, the base voltage of the ON transistor is only about 0.7V, due to the base-emitter diode.
Edit:
I got sidetracked while composing this, and wound up essentially repeating what Nigel said.

 

[Dr.EM]

From looking at the posted design I see a 12VDC power supply connected to a 12V regulator. For the regulator to function properly, the input must be about 3v higher than the output, else the regulator will "drop out", and will serve no function.

 

[bigkim100]

Somebody mentioned somewhere (I wish I could find it...its not part of this thread) a LED Lighthouse circuit for model railroaders that used only a single LED to simulate the ramp up/bright illumination/ramp down effect that they saw in a magazine. Anyone know of this circuit?

 

[kcflyer]

Good catch on the regulator. The so-called 12-volt AC adaptor that I'm using to power the circuit is actually outputting 17.3 volts, which explains why I'm not seeing that problem. I'll make a note on the schematic that the power supply output should be at least 15.5 volts.

 

[audioguru]

The so-called 12-volt AC adaptor that I'm using to power the circuit is actually outputting 17.3 volts.

See, the Chinese person who made it gave you more than 5V for free!

 

[kcflyer]

Bonus! It's one of many I had laying around in a box. It used to go with some long-gone Sharper Image gadget.

Just goes to show: Never trust a label!

 

[philba]

The whole issue of unregulated wall warts is a point of confusion for many beginners. It's not about distrusting the lable but understanding what the lable means. An unregulated DC WW rated for, say, 12V at 1A will read quite a bit above 12V when unloaded. It should deliver at least 12V when loaded at 1A, though. That's why it's not such a simple selection. When feeding a regulator, either choose a higher voltage or higher current rating. Even then, measure the voltage under load to be sure that you are feeding your regulator with a high enough voltage.

 

[kcflyer]

Any advice for outdoor-proofing the circuit? Of course, the whole thing will be kept completely dry under a roof, sealed plexiglas windows and a glass cover. Are there any other precautions for dealing with the temperature swings? Most likely it will be operated only in the warmest six months of the year.

 

[Dr.EM]

It could get warm in there, might act a bit like a greenhouse. Possibly best to use 105c electrolytics (unlikely to get that hot, but they get messy if they fail), can't see anything else being a problem much.

 

[kcflyer]

Here's my updated circuit diagram with some of the suggestions from this thread.

 

[Roff]

The only problem I see is on the 555, where you have 6 connected to 7 instead of to 2. Looks like a "schemo" to me.

 

[audioguru]

It is looking good, except:
Pin 12 of the 4017 is an output that is not used. You don't want to short it to the positive supply because periodically it goes low and high. (I'm a poet!)

 

[kcflyer]

Dang! Right on both counts. Good catch.