Other than that it is much the same except the order of the LEDs is reversed. That's because this one is upside down to the prototype (the Arduino programming socket is now on the right).
The design is the same - 8 LEDs, 8 1k Resistors, 3 x 4 7 pin keypad, Arduino Duemanona - that thing, Uno, Leonardo, just about any Arduino is up to this.
I might add a beeper to this, for the following reasons.
- I've got one in my box of electronic bits.
- I've got some unused Arduino pins
- I can use it to give audio feedback on key presses
- I can (maybe) add some Audio instructions to the NRI832.
With the policy of plausible-in-1972-hardware (like the RAM* and Subroutine system)) though this means that hardware improvements have to be reasonably plausible.
I can't just plug an AY-3-8912 (award yourself 1 retropoint if you know what that is without looking). It would have to be something like a latch feeding a programmable down counter with bit 0 driving a speaker.
One thing that could be plausibly uprated is the speed. As far as I can see the clock speed is completely arbitrary. It could be driven a lot faster - it's stock 74 series TTL which has a propagation speed in nano seconds. It could probably run 50 times faster without breaking sweat. I suppose there wouldn't be much point though.