
A Fourier Synthesis Character Generator - MagicPropmaker
http://www.glensstuff.com/fouriersynthchargen/fouriersynthchargen.htm
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sabalaba
Amazing find! I really think everybody should check out the rest of his
website, it's full of gems. I especially like his Telefunken's Bouncing Ball
implementation.[1] Ever since I took a dive into hardware, I've been excited
by the possibilities of analog computing.

It's great to see fun and stimulating examples that you (might) be able to
reproduce yourself. Also, his Analog Computing Bookshelf photo is very
cool.[2]

Anybody else on HN have experience / pointers on where to find more stuff like
this w.r.t. analog computing?

[1]
[http://www.glensstuff.com/ballimkasten/ballimkasten.htm](http://www.glensstuff.com/ballimkasten/ballimkasten.htm)

[2]
[http://www.glensstuff.com/analogbookshelf/analogbookshelf.ht...](http://www.glensstuff.com/analogbookshelf/analogbookshelf.htm)

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avinium
These are some absolute gems here, great find.

As someone with little experience in hardware, what kind of cost would you be
looking at for the oscilloscope?

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pjc50
About $200. The one shown is an antique from the analog age:
[http://w140.com/tekwiki/wiki/422](http://w140.com/tekwiki/wiki/422)

Various 20MHz secondhand scopes are available on ebay and suitable for
beginners. Delivery is usually expensive as they are heavy, the CRT ones even
more so. If you want more bandwidth the cost goes up exponentially.

You can get ones that are cheaper and use a PC interface, but they have other
limitations and lack a certain authenticity.

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ChuckMcM
I was just talking about this sort of thing with a friend. I really admire the
'all in' analog (or analogue :-)) mode in which he built it. I would be sorely
tempted to do it with a DSP chip and an AD9361 :-).

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mmastrac
> It probably doesn’t need to be said that figuring out the Fourier components
> values for each character, and thus the resistor values of the R.O.M. board,
> was a particularly tedious and laborious task. Each character was first
> traced out on to graph paper. As a periodic waveform is a closed function,
> once the character was manually scribed, the curve had to be closed by a
> segment of a length commensurate in proportion with the time of the blanking
> interval to the net 50 uS period. This was achieved by measuring the total
> length of the visible portion of the characters curve with a length of
> string. The string was then cut down in length to the correct proportion
> (six eighths visible to two eighths blanked) and then used as an aide to
> trace out the segment length closing the curve.

This seems like a fun math problem to solve - given some basic character
traces, create the appropriation using the given harmonics.

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tasty_freeze
Fourier analysis and Fourier synthesis are two sides of the same coin.

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debbiedowner
Great post, I'm intrigued!

I don't know how an oscilloscope works... can someone tell me how the 4*5 1D
sin/cos functions are related to the 2D image of the number 2?

It's obviously not the sum... I also don't think the 2 has been separated into
small 2D chunks in which each one has some of the sins/cos?

I know harmonic analysis well but I'm not getting where the Fourier part is
here

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crististm
It's the sum of the sin/cos with coefficients. There are two outputs, one for
X and one for Y that draw the shape of the number without "raising the pen".

He describes how he calculated the coefficients by drawing the shapes on paper
first.

~~~
debbiedowner
Ah okay he is plotting x(t) vs y(t) to make 2d images where x is a sum of
sines and y is a sum of cosines. These are called Lissajous figures.

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reality_inspctr
Feels like a faintly real version Mary Malone's computer from The Amber
Spyglass book...

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ncmncm
I really like how the image drifts in the last 2 seconds of the video.
Analogue indeed.

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Zardoz84
Great! My father would loved this.

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mattcaldwell
So this won't make a new D&D character for me?

