Below is a demonstration of using a small number of pins to drive a large number of servos using 74HC595 shift registers.  The shift registers are serial-in, parallel-out, with latch.

This is pretty low-tech, and I’m sure many people have done similar things before.  The demonstration was actually testing two things, one being the overall method (including software design) for manipulating a large number of servos using shift registers, and the other being the fabrication of the circuit board itself.

There are many places online where people describe using toner transfer.  The concept is simple.  Just use a laser printer to print the circuit, and then use heat to melt the toner off of the paper and onto the copper surface.  Etching solution removes copper where the toner is absent, and then the toner is scraped off the copper.  Easy.

The tricky part is getting the toner to stick to the copper when melted, and to not stick to the paper.  Ordinary paper is extremely poor for this purpose because the toner much prefers to adhere to the paper rather than the circuit board.  Special-purpose papers designed specifically for toner transfer are available, but they are rather expensive.  Some of the glossy paper intended for inkjet photo printing is said to be good, but I haven’t done enough research to know which is best.

One person had suggested magazine paper, which worked well for me, and has the added advantage of being very inexpensive.  I have not directly compared it to glossy photo paper, but it worked about as well as I could have hoped.

I also found that sanding the copper surface with 220 grit sandpaper improves the adhesion.  Someone online had recommended 600 grit sandpaper, but it is too smooth, and adhesion is poor.  I notice a big improvement with 220 compared to 600.

Some folks also suggest using wax paper and some suggested kitchen parchment.  DO NOT USE THESE.  For one, it doesn’t work, and in addition it will mess up your printer.  In my case the toner did not adhere at all to the paper, and it came out as a powder which fell off the page and made a mess.  Regular documents did not print properly until I had fed several sheets through, and even now the printer does not print perfectly.

I may try some photo paper for my next circuit board, but until then, the recipe I have seems to work fairly well: a magazine page and 220 grit sandpaper.  Oh, and I use a regular iron.  I haven’t optimized the temperature but it seems I don’t need to.