I'd suggest switching over to the attiny84A it's lower power and is basically the same chip but with more I/Os. If you're switching to SMT then you might as well.

I don't think the 85 has enough, but you might be able to juggle the I/Os with more dipswitches. IE: Have one switch determine input/output mode, then another set of switches flip on the physical IOs to a serial interface pinout and password selection IOs. You could also have something like a 4 or 8 pin dip switch with a shift register to interface a longer password list.

Thanks Doug for your comment.

You are right about the ATTiny84A that has more IOs yet the EEPROM is still the same a the ATTiny85 (512B).

I used the Tiny85 as a proof-of-concept and I was facinated by its capabilities given its 8-pins. In fact, I was thinking of taking the project to the next level by using a microcontroller with built-in USB device functionality (ATMega32U4 or STM32F103), bigger EEPROM size, rotary encoder to cycle through the passwords, and a small LCD to display the password (in case the host device doesn't have USB-host functionality). In addition of course to preserve the "Memory Stick" size.

Right now, the bottle-neck is my SMT soldering skills which I need to work on.

Thanks again

Michael

Really neat project. I've built something similar. My device only stored a few login procedures though. I like the dip switch package for accessing multiple passwords without adding a bunch of buttons. Have you thought about adding an application interface to allow passwords to be added without reprogramming the chip?

Thanks Matt for the nice comment.

This is a good idea, and I was thinking of a way add new passwords over serial port. However, this will require using a bigger controller as the ATTiny85 IOs are fully consumed.

What do you think?