Electronic – DIP Switch Connection to I2C EEPROM

For straight-up development boards (for your internal use), I go with a solder jumper or put two back-to-back (3 pads) to make an SPDT switch (here's a footprint I use). If it's small enough, it's fast to both close and open with a touch of solder or desolder braid. Using an actual resistor makes it much more difficult to rework with a standard iron.

If this is a product (as in, the Atmel STK500 development board is a product), you should use something like jumpers or DIP switches, because you don't want some dumb user poking around your board with a 1000°F iron. I'd tend towards DIP switches if you have more options or you are going to put it in an enclosure, otherwise jumpers would be cheaper.

The main question should be "is this something that will be changed as part of normal use?" If the answer is yes, requiring a soldering iron and skills is inappropriate. If it's something that an end user might modify 1-5 times (or preferably someone skilled, e.g. a lab tech), a solder jumper might be OK.

You are pretty much on track, resistor value is not really critical here, you can use 10K for both resistors, that will work fine.

^{simulate this circuit – Schematic created using CircuitLab}

You can make a thevenin equivalent circuit for the open and closed switch situations, for the closed switch:

^{simulate this circuit}

When you press the switch, you will be driving the base with around 1mA, that should make the transistor drive the 20K pullup low very comfortably (in this case, the transistor should be able to drive hfe*ib through the collector, which will be at least a hundred mA)

When you release the switch:

^{simulate this circuit}

You connect the base to ground through 10Kohm, ensuring you turn off the transistor. Quite simple and effective.