Setting up the Pi
I know that a warm and delicious pie topped with cream springs to mind when you hear the words Raspberry Pi. This however is not the edible kind! The credit card sized computer, which is the current rage in the educational circles, has arrived at Greymouth High School. With the ability to send you a message that your house plant needs to be watered to monitoring your Christmas lights, the Raspberry Pi 3 Model B has the ability to help us explore the world around us.
When Eben Upton set out to create a credit card sized computer he could have not envisaged how it would end up attracting the tinkerers and electronic enthusiasts to adopt and change it to suit all ages and sell like 'hot pies'. A Linux based computer, although slower than a laptop, lends itself to a plethora of activities and a very low power source. Operating an open source software, Raspian, it has a primary silicon chip, which runs many of the components on the main board; the CPU, GPU, memory, USB controllers etc.
The Broadcom System on a Chip (BCM2835) is a microprocessor which contains most of the ARM (Advanced RISC Machine) central processing unit's (CPU) input functions- almost like getting an engine started- and a Videocore 4 graphics processing unit (GPU) which handles the outputs.
The microprocessor is also sometimes called the logic chip, which is a packaged unit of integrated circuitry, usually manufactured from material like silicon present in glass and sand. It is one of the best known semiconductor material in an electronic component because the flow of electrons can be can be controlled. Rather than thinking about materials that conduct electricity; either they do (conductors) or they don't (insulators), it is easier to talk about resistance. This is the ease with which a material will allow electricity to flow through it.
Insulators like silicon can be made to behave like conductors by adding a small amount of impurities in them using a process called doping. If antimony is added, slightly more electron are added than required and it gives it the ability to conduct electricity calling it a N-Type silicon. Add boron instead and some of the electrons of silicon are removed leaving behind 'holes' that work as 'negative electrons' carrying a positive electric current in the opposite way. This is P-Type silicon.
Laying the N-Type and P-Type silicon side by side, almost like a sandwich, makes the electrons behave in interesting ways and helping create electronic, semiconductor-based components like transistors. So what is a transistor? It is a device that acts like a switch or a gate for electronic signals,by regulating current. Made up three layers of semiconductor material, each one is capable of carrying a current. A small change in the current in the inner semiconductor layer ( which acts as the control electrode) produces a large rapid change in the current passing the entire component. A large number are interconnected and baked into a single silicon microchip. Most manufacturers typically integrate these chips. The quad-core processor is a chip with four independent units called cores, that are packaged into a single integrated circuit.
An integrated circuit(IC)is usually categorised by its intended application which is either linear (analog) or digital. Linear IC's have a continuously variable output that depends on the input signal. They are often used in audio and radio frequency amplifiers. Digital IC's operate at only a few levels or states rather than over a continuous range of signal amplitudes. Logic Gates are the fundamental building blocks of a digital IC. Logic gates work with binary data; signals that have only two different states called low (logic 0) and high (logic 1). Binary numbers are base two numbers which increase by the power of two unlike the base 10 numbers. As an elementary building block of a digital circuit, a logic gate, has two inputs and an one output. At any point of time, the terminal is either at a low (0) or high (1) condition represented by the different voltage levels. The low state is usually zero volts (0 V) while the high state is usually five volts positive( +5 V). There are 7 basic logic gates: AND, OR, XOR, NOT, NAND, NOR and XNOR. Using a combination of these logic gates various complex operations can be performed.
The excitement of pulling these out of a box and beginning to set them up was tangible in the Level 1 & 2 Game design and Programming class. As the students explore the logic and programming behind the microchip and the Raspian Jesse (yes, from Toy Story!) operating system, they will look at setting up a moisture sensor to the GPIO and monitor the moisture in the soil of a potted plant. However, this just the first step; the combinations are infinitesimal and I know that the students are eager to get 'baking'.