The Easter Solar Engine

Step 7 NPN Easter Engine

The Easter engine can also be made in the complementary or 'dual' version, with two NPN transistors and one PNP.  The complete schematic is shown in the first illustration here.  The stripboard layout can have the same component locations and the same track cuts as the first or 'PNP' version, the essential changes being switched transistor types and reversed polarity of the solar cell, storage capacitor, diodes and LEDs.  The NPN stripboard layout is shown in the second illustration and incorporates an extra diode D4 for a higher turn-on voltage, and a diode D0 from the base of transistor Q2 to the junction of resistors R4 and R5 for a higher turn-off voltage as well.