This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to remain off. The conducting transistor can be turned off by grounding it's base through the push button which causes the collector voltage to rise and turn on the opposite transistor.

Copyright 2006 Bill Bowden

2x transistor
2x LED
2x push button
2x 470 Ohm resistor
2x 7.5 kOhm resistor