If you've read the previous page, you know by now that handheld calculators need single-chip microprocessors to function. But how do you activate the microprocessor? It all starts with what's on the outside of the device.
Many modern calculators have a durable plastic casing, with simple openings in the front that allow rubber to push through, just like a television remote. By pressing a button, you complete a circuit underneath the rubber, which sends electrical impulses through a circuit board below. Those impulses are routed through the microprocessor, which interprets the information and sends a readout to the calculator's display screen.
The displays of most early electronic calculators were made up of LEDs, or light-emitting diodes. Newer models that use less power incorporate the liquid crystal display, or LCD. Rather than producing light, LCDs rearrange light molecules to create a pattern on the display and ultimately don't require as much electricity.
Early calculators also had to be plugged in or used bulky battery power. But by the late 1970s, solar cell technology had become cheap and efficient enough to use in consumer electronics. A solar cell creates electricity when the photons of sunlight are absorbed by semiconductors, such as silicon, in the cell. This knocks loose electrons, and the electric field of the solar cell keeps them all traveling in the same direction, thus creating an electric current. (Something like an LCD calculator would only need a low-level current, which explains why their solar cells are so small.) By the 1980s, most manufacturers of simple calculators were taking advantage of solar cell technology. More powerful scientific and graphing calculators, however, still use battery power.
In the next section, we'll look more closely into binary code and how the calculator actually does its job.