Just like the relay, the MOSFET pins must be properly identified and wired up correctly.


Note that the MOSFET has a curved side and a flat side, as shown in Figure 8-6.


This is necessary to indicate the proper order of the pins.


Be aware that this order is particular to the 2N7000, but is not necessarily universal.


Other MOSFETs might have a different order of the pins.


You always have to check the data sheet to find the order of pins for your particular MOSFET.


Pay attention to the diodes, MOSFET, and the relay: the diodes are polarized, the MOSFET must have the flat side facing the right way, and the relay needs to have the stripe at the proper end for everything to work.


If you look at Figure 8-5 and Appendix D, you’ll notice that some components, like resistors, light sensors, and (some) capacitors, have circuit symbols that are symmetrical, in that you can flip them upside down and they look exactly the same, while other components, like LEDs, diodes, and MOSFETs, are not symmetrical. Resistors, light sensors, and(some) capacitors are unpolarized, meaning they work the same regardless of which way the current flows through them, while components, like LEDs and diodes, are polarized, meaning they work differently depending on which way the current flows through them. Similarly, MOSFET pins have very specific functions, and can’t be used interchangeably.


While not uniformly true, generally components that have symmetrical schematic symbols are unpolarized, and components with asymmetrical schematic symbols are polarized.