Wednesday, May 30, 2012

TLC5940, TLC5941 and Arduino

The TI TLC59xx chip family are constant current LED drivers that have some pretty impressive stats.  I'm experimenting with the TLC5941 which has 16 constant current channels, 80mA sink capability per channel, 17v maximum LED voltage and 4096 PWM intensity levels per channel.  If you want to use it, here's an Eagle schematic and footprint to get you going:

And here's a photo of 2 quad chip driver boards that I made.

Packing those features into such a small chip has created a device that has got some nasty traps that are not described in the datasheet (or hard to understand) and so it is easy for beginning hardware hackers to either fry a couple of chips or just give up in frustration.  If you are looking into using this chip, check out my experiences after the break.

Friday, May 4, 2012

If you wish to make an apple pie from scratch you must first invent the universe

I recently googled this Carl Sagan quote using the search "if you wish to make an apple pie from scratch meaning" and was pretty dismayed that the top result not only misquotes him but comes from a yahoo Q&A site with the following "best" answer:

"Sagan was merely saying all the elements of an apple pie made from scratch [reduced to the lowest common denominator] are elemental to the universe and the universe had to be there before an apple pie could be made from them.

Hardly profound, though it's often quoted."

This result probably says more about the mental acuity of the analyzer then about what is being analyzed.  Unfortunately answers are "closed" so nothing can be done about the yahoo page.  So I shall give it a shot here and if you like my response please link/forward/facebook/google+ this posting so we can collectively knock Yahoo off of the top spot!  So let me start over:


"If you wish to make an apple pie from scratch you must first invent the universe"  Carl Sagan

You can hear a clip of him saying it straight here:, but you'll probably by a lot more entertained by this remix Symphony of Science: A Glorious Dawn

Literal Meaning

Just so we are all on the same page, the simplest level of interpretation is that the baker's fundamental ingredients are not fundamental at all.  Apple trees produced the apples, wheat plants produced the flour in the crust, sugar cane produces the sugar.  And of course this idea must be recursively applied.  What made the chemicals and matter that these plants used?  The big bang and stars made them out of more fundamental particles and energy.  What made the energy the plants used to arrange the matter?

This is essentially as far as the original "answer" goes,  But this is a trivial analysis.

Let's take a Bite out of this Pie

A great way to analyze a quote is to first make your analysis, and then modify the original quote with a different one that matches your analysis.  Then compare the two and see what the original has that's missing from the new one & what the new one has that's missing from the original.  So here's what Sagan might have said if he was as smart as the author of the "best" answer:

1. God made the universe, you just rearrange it.

Here I am clearly differing by introducing "God" into the quote.  Its possible that Sagan's personal beliefs precluded this formulation (I don't know or care).  But the important point is that the omission of "God" in his quote aims it directly at humanity, at us.

So let's leave God out of the quote:

2. You can't make stuff from scratch because you're always using other stuff that's already been made.

This formulation in the negative is limiting -- but is that what Sagan wanted to say?  That you CANT make an apple pie from scratch?  His formulation is in fact enabling; "if you wish to make...".  He believes that someday we will truly make a pie from scratch and is seeking to define what that means.  By formulating the sentence positively, the quote is infused with the hope and promise of humanity's potential.

So let's reformulate in the positive, but tweak the noun:

3. If you wish to make a particle accelerator from scratch you must first invent the universe

Who is the "you" in this quote?  By choosing something as prosaic, as domestic as an apple pie he implies that the makers shall someday be, well, anybody and the making shall be an everyday occurrence.  By choosing "particle accelerator" I pretty clearly point this at a small esoteric subgroup.  He is also saying that the most common of thing are actually made up of complex ideas.

4. (and finally the misquotation) If you wish to make an apple pie from scratch you must first create the universe.

What's the difference between "creation" and "invention"?  Well, a potter can "create" a clay pot (for example) by throwing clay on a wheel.  But how can she "invent" one?  She really cannot; its already been invented.  But she can invent a new kind of pot.  With the term "invent" Sagan is clearly suggesting not the mechanical act of creation but the mental act of invention.  It is not enough for us to create the pie from fundamental particles; to truly make it "from scratch" we must invent (and therefore understand) the entire mathematical/informatic/computational underpinnings of the universe that either must have been before the first particle existed or that was forced to be by that particle's existence.

Actually, I'm still struggling with what he meant by invent.  Since the universe already exists it cannot really be invented again.  Was he suggesting the actual invention and subsequent creation of new universes by humankind?  Or was he implying that inventing the universe would allow the controlled creation of space and matter within our existing framework?   ...quantum mechanics predicts that particles and antiparticles are spontaneously created all the time...

Regardless, in this one sentence Sagan has left us with a large, tasty slice of his hopes and dreams for the future of science and humanity!