I've used BOTH NPN and PNP bipolar transistors to flash four coloured LED's.
* The SPST switch is in the NO position. Flick the SPST switch to the NC position and WAIT A FEW SECONDS for the simulation to begin.
* If the SPST switch is in the NC position when you power up the circuit, WAIT A FEW SECONDS or simply shake your smartphone or tablet to begin the simulation.
* Alternatively, press one of the push buttons located near the power source and the simulation will begin immediately.
