Yup, on my third time now. There's reading, there's comprehending, and there's retaining. Makes a little more sense each time.

I'm sure the PWM thing will come to me. For now I'll just skip it.

 

Shouldn't it connect to 16? Vdd? The Vdd - Vss thing still confuses me. And of course Vcc.
Google is my friend.

Unless 4015 and 4015B are different. Or I've read something incorrectly. More things to watch.

Oops. Yeah, pin 16.

 

How firm is your grasp with Ohm's Law. Run the scenarios on a LED circuit using 12V and 13.7V.

 

Ok at the risk of illuminating my ignorance. I did that yesterday - went to the math instead of a calculator so I could do it backwards. If I ran the formula correctly. LED VF = 2.8, 20 ma. If I set the circuit at 13.6 I use a 120Ω resistor. Then if the voltage drops to 12 I only have 6 2/3 ma available. If this is not correct please let me know and I will run back through it and find my error.

Using the calculators on various sites does not make this correlation obvious.

This is when I noted that I had a new appreciation for the idea of a regulated supply.

I will continue to study. Every time I go over this stuff it sticks just a little bit more.

 

If you want an idea of the type of LED to look for, here's an example:
http://www.goldmine-elec-products.com/prodinfo.asp?number=G16750

Very bright, the correct color (red-orange, ~628nm) and a fairly wide viewing angle (60°) in a DIP package for ruggedness and heat dissipation.

You won't want to look at one of these directly when it's on full blast. They are BRIGHT!

 

I keep a scientific calculator next to my keyboard just for these kind of problems. The build in calculator Windows provides just isn't the same.

 

I don't know if we are on the same page. I was using the various LED calculators on line that supply resistor values. When you plug the particulars in for various voltages the resistors output don't seem to vary by much. This gives the impression that the differences are not very large.

Actually doing the math the other way around gives a whole different perspective.

Scientific calculators have entirely too many buttons.

 

I never use online calculators. You can't know where their assumptions are, and you really learn a lot more doing this kind of math yourself, the most complicated part is multiplication and division.

Working current through LEDs is brute simple, but you have to know Ohm's Law.

Just for convenience I have this tester.

http://www.bgmicro.com/LED1063.aspx

It lets me check LEDs on the quick, plus allows me to take a quick reading on the Vf of that particular part. Before that I was using a variable resistor, a 100Ω resistor (to measure current), and a 9V battery and clip.

 

Will that thing check piranhas? Information on the site was a titch limited...

I am now at the point of having so much information that I can't decide what to order. I may need to simmer for a couple of days. (Like if I go with a 556 timer instead of the 555; can I combine circuits on one board; what was that about a pic...), those questions are all rhetorical.

 

Since I've been learning so much here the last several weeks, I thought I would go ahead and see how hard it is to solder these little parts with my new iron. Now I have learned how long an LED lasts when you run full power through it. It's a 1 with a bunch of zeros in front of it.

 

Actually its a 3 with a bunch of zeros