Drive a shift register with one pin...

[westfw]

Someone should implement this on an Arduino.  You probably need to add a cap to slow the process down to digitalWrite() speeds, but it should still work pretty well!

http://www.edn.com/article/518373-Drive_16_LEDs_with_one_I_O_line.php

[CrossRoads]

Interesing oncept.  Could be handy in situations needing just a little external hardware.

Not so handy where there might be several shift registers sharing a common data line & clock, with unique output load lines, where parallel output update is needed.

I wonder - is shiftout interruptible? If so, that might lead to some glitches in the output.

[Grumpy_Mike]

What a hairy concept. I can't see that being to reliable over the long term or very reliable as it relies on the input capacitance of pins. This will change with different chip manufacturers.

[CrossRoads]

I read it as onewould install an external resistor/cap to work with the timing of the source part.

[CrossRoads]

Hmm, I guess it does show the internal capacitance.
I still think I'd exgternal, determined empirically to work with the shfitout, or more practically the SPI which should have fixed hardwre, timing and the particular logic family being used.