Soldering Your Own Switch
If you purchased one of the circuits without a switch then you can easily attach your own switch as follows:
Solder one end of your switch to the pad labeled "SW+" and the other to the pad labeled "SW-" If you have an additional button you'd like to use as a hard-reset button then you can wire the leads of that switch to "RST+" and "RST-".
The circuit will auto-detect whether you are using a momentary switch or a discrete on-off switch
For users who are soldering NES power switches to the circuit, this diagram should help: