Components in Electronics Circuits

Here, we will briefly discuss the most common components you will encounter in electronics, their symbols in circuit diagrams, and why we use them in electronics. These components are all the small electronics pieces that are attached to a printed circuit board (PCB) or inserted into a breadboard.


If you think of electrical current as water flowing in a channel, resistors would be gates that limit the flow of the water. Resistors limit the flow of electrons in an electrical system. They are often very small and made of carbon or ceramic. Resistance is measured in a unit of Ohms, represented by the symbol Ω (Omega) and is equivalent to Volts per Amp. The resistance value of a resistor is often indicated by the color code show below in the chart generated by Digikey. Resistors are represented by the letter “R” in circuit diagrams with the symbol as indicated below.






Diodes only permit the flow of current in one direction. Picking up from the water analogy used in resistors, diodes would be like a one-way valve or gate, letting water flow through in only in one direction. Due to their nature, it does matter which way these components are oriented in the circuit. Current will only flow through when positive voltage is applied to the anode (or negative terminal) and negative voltage to the cathode (positive terminal). Diodes are indicated using the letter “D” on circuit diagrams and are represented by the symbol below.





Inductors are a coil of wire wrapped around a ferric (iron) core that when placed in a magnetic field generates a current and induces a voltage. In the radio application the inductor’s specific task is to transform the electromagnetic waves of the radio signal into an electrical current. Inductance is measured in units of henry, or H, which is equivalent to a Volt second per Amp. The letter used to represent inductors on a circuit diagram is “L” and the symbol is shown below.





Capacitors can store electric charge temporarily for uses where a large amount of current is needed for a short burst. There are two main types of capacitors. The first is ceramic, they look like little Advil pills; these are not polarized, that is, their orientation does not matter. The second type are electrolytic, these are often blue or back cylinders with two different length terminals. The shorter terminal is the anode, or negative terminal, and the longer terminal is the cathode or positive terminal. Often their polarity is indicated with a +/- sign. Capacitance is measured in farads (F), or more commonly in small electronics projects, microfarads (µF), which are equal to an Amp second per volt. Capacitors are represented by the letter “C” on circuit diagrams and by the symbols below.





A transistor is a simple switch that can either be used as a switch, as digital logic, or as an amplifier. Transistors have three pins, a collector, a base, and an emitter. They are categorized as either a N-type or P-type, where the N-type permits a large current to flow when a small current flows (amplifier), and the P-type acts more like a voltage-gated switch. The transistor used in this radio is a N-type or amplifier. Transistors often have a flat side and a rounded side to help determine their orientation. They are represented by the letter “Q” and the symbol shown below.




There are many different types of buttons, the most common are called momentary push buttons or momentary push switches. When the user presses down on the button, an electrical connection is made briefly during button press, which redirects the flow of current for a short period of time. Depending on the circuit, the button can have many different actions. Buttons are typically represented on a circuit diagram with a few letters or short phrase indicating what the button’s function is; the symbol is shown below.





An LED light bulb is simply a diode that also emits light. It functions in the same was as a regular diode, ensuring current only flows in one direction. An LED is indicated on a circuit diagram by the letters “LED” and the symbol shown below.





Header pins are simply metal pins that are designed to attach to breadboards and PCB’s for easy and temporary connections to other devices or circuits without soldering. A jumper sleeve is a small sleeve that fits over two or more header pins to connect them in a circuit. Header pin locations are often indicated on a circuit diagram by an open terminal with labels for the individual pins, see the image below.






The batteries are held in a battery holder that already has the wiring between individual batteries built in and connects to the circuit on the breadboard PCB with two wires – a red positive voltage wire, and a black negative voltage wire. Battery power supplies are often indicated on circuit diagrams by the letters “PW” or “PWR” or sometimes just by their voltage rating, such as “3V”. The positive and negative terminals are almost always indicated with “+” and “-“ signs. The symbol for a generic supply of power is shown below.



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