CHAPTER 26 ■ SMOOTHER, SMALLER, CHEAPER
Like most new electronic devices, the modern Sandwich is powered by a rechargeable lithium polymer
battery, rather than a classic 9 V alkaline. The lithium polymer battery has a voltage of about 3.7 V, which
directly supports more recent electronic parts without requiring voltage-regulating circuitry.
Looking at the schematic in Figure 26-5, notice that the modern Sandwich retains aspects of the basic
model, even down to many of the part numbers. The most obvious change is a 32-pin microprocessor brain
instead of an 8-pin comparator chip.
Figure 26-5. Schematic for a modern Sandwich robot
Don’t panic! This robot has the same basic circuit elements presented earlier in this book; the
schematic just looks busier.
- The LEDs are now individually wired instead of in series. Because the 9 V battery
has been replaced with a 3.7 V lithium polymer battery, there is no longer enough
voltage to power the LEDs in series. - The white LED headlamps and the sensors are now powered by transistor Q9. This
is the same method of supplying power that the Sandwich motors have always used.
This allows the microcontroller to turn off this circuitry to save power, if desired. - The power and line-following switches have been replaced by pushbuttons. Through
the transistors, microcontroller pins, and microcontroller commands, all power is
now controlled by software. Likewise, light and dark line-following modes can be
detected algorithmically rather than set electrically.