You may remember in the old days, when computers hade RS232 serial ports you could use to make a very cheap pic programmer with just a few resistors and diodes, maybe a capacitor. You could then flash an MCU to make a more usable programmer and the chicken and egg problem was solved.

Nowadays, computers no longer comes with serial ports. Of course you can buy a really cheap usb->serial converter, but they are not really great for bitbanging (because the delay between each usb package is rather long, and for bitbanging you want to send lot and lot of small packet).

I was thinking about the best way to bitbang a protocol without a microcontroler, and start thinking of perforated cards, barcodes... and thought it might be possible to read a protocol printed on paper with phototransistors.

I hade to try.