Electronic Components & Circuits
A broad reference to parts, instruments and circuit functions, explained in everyday language with labeled illustrations, examples and specification checks.
How to use this list
Open an entry to see its illustration, what it does, an example and the specifications that matter. Tap any image to enlarge it. Images are original representative illustrations, not photographs, exact pinouts or guarantees of physical identification. Component families and circuit arrangements are distinct: a capacitor is a part; a filter is a circuit that may use several parts. This reference covers common and important families, rather than every manufacturer part number or specialized circuit ever made.
Examples explain function; they are not universal replacement or wiring instructions. Appearance, package size and a matching nominal value do not establish compatibility. Stored charge, mains, vehicle batteries and high-voltage equipment require appropriate precautions and qualified procedures.
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Cable, shielding and twisted pairSwitches, Relays and Connectors
What it does
Conductors and their arrangement carry power or signals; shielding and pairing can influence interference behavior.
Example
Audio, data or sensor connections.
Important distinction
The cable and grounding arrangement should match the intended interface.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Connector, terminal and headerSwitches, Relays and Connectors
What it does
Provides a removable electrical or mechanical interface.
Example
Board-to-board, wire-to-board or panel connections.
Important distinction
Pin assignment, keying and current rating must be confirmed; a fitting plug is not proof of compatibility.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
DPDT and rotary switchSwitches, Relays and Connectors
What it does
A DPDT provides two coordinated changeover poles; rotary switches can select among multiple positions.
Example
Polarity selection in an approved trainer or source selection.
Important distinction
Mechanical position alone does not establish the internal contact arrangement.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Electromechanical relaySwitches, Relays and Connectors
What it does
Uses a coil-operated mechanism to control contacts.
Example
Switching a separate load from a control circuit.
Important distinction
Coil and contact specifications are independent requirements.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Pushbutton and reed switchSwitches, Relays and Connectors
What it does
A pushbutton changes contacts through manual movement; a reed switch responds to magnetic influence.
Example
A user control or position detector.
Important distinction
Normally open/closed and momentary/latching behavior must be specified.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Rotary encoder versus rotary switchSwitches, Relays and Connectors
What it does
An encoder reports movement or position as encoded information; a rotary switch selects contact paths.
Example
A menu knob or source selector.
Important distinction
Similar mechanical movement does not imply the same interface.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Socket, jumper and test pointSwitches, Relays and Connectors
What it does
A socket holds a removable component, a jumper selects a connection, and a test point provides access to a defined node.
Example
Service access or configuration.
Important distinction
An accessible node is not automatically a safe reference or an authorized connection.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Solid-state relaySwitches, Relays and Connectors
What it does
Uses semiconductor switching controlled through an input arrangement, often with isolation features.
Example
A suitable automated-load circuit.
Important distinction
Output technology, leakage, heat and AC/DC suitability vary.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
SPST and SPDT switchSwitches, Relays and Connectors
What it does
SPST provides a single switched path; SPDT selects between two paths from a common pole.
Example
On/off control or signal selection.
Important distinction
Contact rating, load type and required isolation matter.
Specifications to read
Contact or interface assignment, voltage/current, load type, keying, mechanical requirements and insulation.
A rating is a limit or condition, not a guarantee of suitability. Use the manufacturer's data sheet for the exact component and the equipment's schematic for its intended role.
Visual comparison guides
Compare representative physical forms, then read the entries for their different functions. Many parts share package shapes. Appearance alone cannot identify ratings, internal construction or terminal assignments.
Units and worked examples
| Quantity | Unit | Meaning |
|---|---|---|
| Voltage | V, volts | Potential difference between two points. |
| Current | A, amperes | Rate of charge flow. |
| Resistance | Ω, ohms | Resistance to current flow. |
| Power | W, watts | Rate of energy transfer or dissipation. |
| Capacitance | F, farads | Charge change per voltage change. |
| Inductance | H, henries | Relationship between current change and induced voltage. |
| Frequency | Hz, hertz | Cycles per second. |
Prefixes: k = 1,000; M = 1,000,000; m = 0.001; μ = 0.000001; n = 0.000000001; p = 0.000000000001. Case matters: M and m are different.
Resistor example
For an ideal 1 kΩ resistor with 5 V across it: I = V/R = 5/1,000 = 0.005 A = 5 mA. Dissipation is P = V²/R = 25/1,000 = 0.025 W. This arithmetic does not select a real part without its temperature, voltage and application requirements.
Tolerance example
A 1 kΩ resistor with ±5% nominal tolerance spans 950 Ω to 1,050 Ω at the specified conditions. Tolerance is different from drift with temperature or aging.
Capacitance and timing example
10 μF = 10,000 nF. An ideal first-order RC network with R = 1 kΩ and C = 10 μF has τ = RC = 0.01 s = 10 ms. A time constant is not automatically the delay of every timer using those parts.
Stored energy
Ideal capacitor charge is Q = CV; stored energy is E = ½CV². Doubling voltage at the same capacitance quadruples the stored energy. These are learning equations, not a discharge procedure.
Schematic symbols, labels and markings
Reference letters identify components in a drawing; conventions vary by manufacturer and standard. Always read the drawing's legend.
| Common label | Often used for |
|---|---|
| R | Resistor |
| C | Capacitor |
| L | Inductor |
| D | Diode |
| Q | Transistor |
| U / IC | Integrated circuit |
| T | Transformer |
| K / RL | Relay |
| SW / S | Switch |
| J / P / CN | Connector |
| F | Fuse |
| Y / X | Crystal or resonator |
| TP | Test point |
| V / VT | Tube in some historical documentation |
R17 identifies a component location, not a resistance value. A marking such as 4R7 may mean 4.7 Ω in an applicable resistor convention. Three-digit markings such as 104 often represent 100,000 base units: 100 kΩ for a resistor or 100,000 pF = 100 nF for an applicable capacitor code. Confirm the component family and marking system; short codes can be ambiguous.
Common questions
Can I replace a part with any higher-rated one?
No. A higher headline rating does not ensure suitable function, polarity, frequency behavior, package, protective approval or circuit stability.
Does a part that looks normal have to be good?
No. Visual observations can help, but many electrical changes leave no obvious external sign.
Are capacitance, ESR and leakage the same?
No. They describe different properties. A single test cannot establish every capacitor failure mode.
Can I measure every component while it remains connected?
Other paths can affect an in-circuit result. Interpretation depends on the circuit and instrument. Internal work also requires a suitable qualified safety procedure.
Does a matching package establish a transistor or IC replacement?
No. Pinout, function, voltage, drive, timing, heat and application requirements must match.
Is a component the same thing as a circuit?
A component is a building block. A circuit connects building blocks to perform a function. The same component family can serve many circuit roles.
How do I begin learning?
Start with units, schematic labels, resistor/capacitor/inductor functions and signal-versus-power paths. Use disconnected parts or an instructor-approved low-voltage trainer before considering customer equipment.
Is this reference free?
Yes. Every entry, example and reference on this page is public. The separate repair masterclasses have their own free previews and paid lessons.
Manufacturer references
Original plain-language summaries and educational examples. These references support further study; exact product data sheets and equipment manuals remain authoritative for a real application.
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