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Electricity is briefly defined as the flow of electric charge, but there's much more to it. When dealing with electronics, you will be dealing mainly with current electricity. However, you may find yourself asking, "Where do the charges come from? How do we move them? Where do they move to? How does an electric charge cause mechanical motion or make things light up?" To begin to explain electricity, we need to zoom way in, beyond the matter and molecules, to the atoms that make up everything we interact with in life. Dive in or get a quick refresher with our tutorial on the natural phenomenon we call electricity.
In general, more power means more energy. We can calculate power using the various SI units from above. Energy is measured in terms of joules, and power is a measure of energy over a set amount of time; therefore, we can measure energy as joules per second, which is also known as the "watt."
For example, the power adapter from the wall outlet that charges your phone is a common type of connector. If it plugs into another connector, then it is said to be a male connector, if it gets plugged into by another connector then it is a female connector. Most connectors have a polarity; for example, modern wall plugs have two different widths for the plug blades. This connector is polarized because it will only plug into the wall one way. If you want to learn more basic connector terminology, identify polarized connectors and learn which connectors are best suited for certain applications, you can follow along with our tutorial.
If no load is present in the circuit, it's a short circuit. This is dangerous, because there is nothing to restrict the current flow, and you can end up with burned wires, damage to the voltage source or a quickly-drained (or exploded!) battery.
With a constant voltage source, we can see how current and resistance change. With a high resistance, there will be very low current flowing through the load. With a low resistance, we will see the opposite. We can use Ohm's law in conjunction with the power equation to determine any electrical characteristic (power, voltage, current, or resistance) as long as we know 2 of the other quantities. To get a full understanding of the relationship between voltage, current and resistance, view our tutorial on Ohm's Law.
The trusty o-scope is very versatile, and is useful in a variety of troubleshooting and research situations, including:
- Determining the frequency and amplitude of a signal, which can be critical in debugging a circuit's input, output, or internal systems. From this, you can tell if a component in your circuit has malfunctioned.
- Identifying how much noise is in your circuit.
- Identifying the shape of a wave -- sine, square, triangle, sawtooth, complex, etc.
- Quantifying phase differences between two different signals.
Analog signals are a smooth continuous plot, with voltage on the y-axis and time (usually in seconds) on the x-axis. An example of an analog signal can be seen in figure 6. Some of the most common analog components are resistors, capacitors, inductors, diodes and transistors.
Digital signals must have a finite set of possible values. Most digital signals oscillate between two fixed values. An example of an analog signal can be seen in figure 7. Most communication between integrated circuits is digital, such as serial communication, I2C, and SPI, which we will go over in more detail later.
Digital signals are easier to work with because they consist of only two fixed values. For example, if the digital signal outputs 5V, we can convert that into a 1 in binary, which would portray an active pin (high pin). If 0V is the output, we can convert that into a 0 in binary, which would show the pin is off.
When current flows into a capacitor, the charge gets stuck on the plates when it can't get past the insulating dielectric. Because the electrons are stuck to one of the plates, the capacitor becomes negatively charged. The negative charge on one plate pushes away similar charges on the opposite plate, making it positively charged. The stationary charges on these plates create an electric field that influences voltage, resulting in the capacitor becoming charged. You can calculate the charge in a capacitor with the following equation.
Here, dv/dt is the derivative of voltage. If the voltage is constant, then the current going through the capacitor is 0 because the derivative of a constant number is 0. This is why current cannot flow through a capacitor holding a steady voltage.
To get a better understanding of how inductors work, imagine putting an inductor in parallel with a lightbulb that is in series with a voltage source and a switch. As the switch is closed, the bulb will light up but the intensity of the lightbulb will decrease. When the switch is turned off, the brightness of the bulb will gradually decrease. You can attribute this behaviour to the inductor placed in parallel with the bulb. When you close the switch, current flows from the voltage source through the bulb, causing it to light up. At the same time, current flows through the inductor coil. This generates a magnetic field in the space surrounding the coil. The magnetic field varies in the short time the current builds up. The changing magnetic field induces a current to flow through the coil. However, according to the rules of electricity, this current is opposite to the original current sent by the voltage source, so the effective current through the coil increases with time while decreasing the current passing through the bulb. This causes the bulb to reduce its glow from bright to dim.
When you open the switch, the magnetic field falls. During the fall of the field, the induced current causes the voltage across the inductor to rise for a moment. This causes the bulb to brighten up briefly. When the current reduces to zero, the bulb turns off.
Current trying to flow the reverse direction is blocked. If the voltage across a diode is negative, no current can flow and the resulting circuit acts as an open circuit; in this situation the diode is said to be reverse-biased. A diode has two terminals: the anode (positive terminal) and the cathode (negative terminal). Below is a chart regarding diode characteristics.
There is a third characteristic of a diode called breakdown. When the voltage applied across the diode is very large and negative, a lot of current will be able to flow in the reverse direction, from cathode to anode.
Using just two series resistors and an input voltage, we can create an output voltage that is a fraction of the input. Voltage dividers are one of the most fundamental circuits in electronics. You may see them drawn a few different ways, but they should always essentially be the same circuit. And remember, any part of your system that pulls current is kind of like adding another resistor to the network, so don't forget to include all potential loads on any nodes!
One side (parallel) consists of data lines, and the other side (serial) has the transmit (TX) and receive (RX) lines. Never connect TX to TX and RX to RX! The wires should cross, TX should be connected to RX, and RX should be connected to TX between the separate serial communication devices. UARTs do exist as stand-alone ICs, but they're more commonly found inside microcontrollers.
SPI works in a slightly different manner than serial communication - it uses a synchronous data bus rather than an asynchronous data bus. With this in mind, it uses separate lines for data and a clock that keeps both the receiving and transmitting side in perfect sync with one another. The clock is an oscillating signal that tells the receiver exactly when to sample the bits on the data line. This is either the rising or falling edge of the clock signal. When the receiver detects that edge, it will immediately look at the data line to read the next bit. One reason SPI is popular is that the receiving hardware can be a simple shift register - simpler and cheaper than the UART, which is required by asynchronous serial communication.
Like SPI, it is only intended for short distance communications within a single device. Like ASIs (such as RS-232 or UART), it only requires two signal wires to exchange information. SparkFun's Qwiic Connect System takes advantage of the benefits of I2C to allow different sensors, actuators, displays and more to be daisy-chained together with a polarized cable.
Getting started with basic electronics is easier than you might think. This Instructable will hopefully demystify the basics of electronics so that anyone with an interest in building circuits can hit the ground running. This is a quick overview into practical electronics and it is not my goal to delve deeply into the science of electrical engineering. If you are interested in learning more about the science of basic electronics, Wikipedia is a good place to start your search.
With alternating current, the direction electricity flows throughout the circuit is constantly reversing. You may even say that it is alternating direction. The rate of reversal is measured in Hertz, which is the number of reversals per second. So, when they say that the US power supply is 60 Hz, what they mean is that it is reversing 120 times per second (twice per cycle).
With Direct Current, electricity flows in one direction between power and ground. In this arrangement there is always a positive source of voltage and ground (0V) source of voltage. You can test this by reading a battery with a multimeter. For great instructions on how to do this, check out Ladyada's multimeter page (you will want to measure voltage in particular).
Speaking of voltage, electricity is typically defined as having a voltage and a current rating. Voltage is obviously rated in Volts and current is rated in Amps. For instance, a brand new 9V battery would have a voltage of 9V and a current of around 500mA (500 milliamps).
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