# Series and Parallel Circuits

All hams should have at least a limited understanding of basic circuits, and this means being able to differentiate between series and parallel components.

Besides numerous license exam questions (dozens below in green boxes; knowing helps you pass the exams), some technical discussions in ham radio will throw the terms around so let’s explore the matter here.  In addition to our own presentation, some excellent web references are given at the end for further (and often more interesting) information.

Before jumping into circuits, let’s discuss series and parallel connections.  Visualizing this will help us understand series and parallel circuits.

As the name suggests, series connections are lined up end-to-end.

We’re demonstrating with resistors but the principle applies to any two-terminal component: capacitors,  inductors, diodes, cells/batteries, and light bulbs can all be wired in series with two or more of each (or a mix of different parts).  Lining them up terminal to terminal makes a series connection.

Schematically, 3 parts in series looks like this:

From this simple schematic we intuitively see that the current flowing through a series string has to be the same though the chain; there is nowhere else for electrons to flow (current).

Equal current is one way of defining a series circuit.

Also as the term suggests, parallel connections are side-by-side.

Again, demonstrating with resistors and again, the principle applies to any two terminal component.  Arranging components across each other makes a parallel connection.

Schematically, 3 parts in parallel looks like this:

From this simple schematic we intuitively see that the voltage across parallel components must be the same.

Equal voltage is one way of defining a parallel circuit.

We just learned that current is the same through components in series, and voltage is the same across components in parallel.  What about  the voltage across series components, and current through parallel components? Continue reading

# LEDs

The light emitting diode (LED) comes in a wide variety of sizes, shapes, and colors, and is something every ham should be familiar with.  There are a number of exam questions related to LEDs.

LEDs are more common than you may realize.  Not only used on ham radio equipment, they are typically found on most electronic gadgets, primarily as indicator lights, most often as power or status indicators.

Developed in the early 1960s, visible LEDs became practical replacements for miniature incandescent lamps in the 1980s.  Their main advantage is in efficiency (wasting little power), but they also last many years and illuminate instantly, all compared to incandescent light bulbs.

The above question phased out of the General class exam pool in 2019 but it speaks to the benefits of LEDs over other technology.  This example from the Tech license exam pool shows an LED being used in a traditional power supply circuit as a power indicator:

Useful as more than just on/off indicators, LEDs, when grouped, really open up interesting applications.  When formed as bars in a figure 8 arrangement, the classic seven segment display is created:

This revolutionized electronics to display numbers quickly and inexpensively and were an early use of the technology starting in the 1970s.

Also, when different color LEDs are bunched together their combined light can form a different color, often to achieve white.  This is the principle of LED back lighting for flat panel displays and for the recent adoption for home and general lighting (replacing light bulbs).

White LEDs (or a blend of other colors to make white) weren’t practical until the mid-1990s, and it took years to become economical.  The widespread use of LEDs for display back lighting and general lighting is now less than 15 years old.

For those interested in the technology, we’ll dive into some of the details of LEDs now.  As the name implies, an LED is a form of diode, the simplest possible semiconductor device formed by Continue reading

# Electronic Connector Types

Earlier we reviewed RF connector types commonly used in ham radio applications.

There are also a number of common electronic connectors used in amateur radio that you should be familiar with to have a working knowledge of equipment interconnect and interfacing.

Presented below are eight common non-RF connector types.  Some are for power but most carry audio or control signals between devices and equipment.

D-sub

D-subminiature connector commonly called D-sub.  Name derived from its general “D” shape with one side longer than the other.

Five shell sizes 1-5 (A thru E).  Standard and high density for all five shell sizes.   9-50pins standard, 15-78pins HD.

Ham radio general purpose use such as control interface; also for serial (RS-232) communication plus video between PC and monitor.

Reference here.

RCA

An old, simple, and cheap design still widely used for audio and video signals.  Sometimes called phono plug and jack.

Typically used for L and R stereo audio channels with white and red color coding.

Reference here.

Phone, 1/8″ (3.5mm) and 1/4″ (6.35mm)

Another old and reliable design still widely used for audio signals.

1/4 standard and 1/8 mini plug/jack sizes are the most common.

Two wires for mono signals, three for stereo.  A four pole version is occasionally used with two ring contacts.  In ham radio use this might be a HT with speaker, mic and PTT switch; three functions sharing a common fourth terminal.

Reference here.

Mini-DIN type

DIN is an acronym for Deutsches Institut für Normung, the organization for German national standards.  The DIN standard encompasses a wide variety of electrical and electronic connectors. As used in ham radio the specific subset of Mini-DIN is what we normally encounter.

The Mini-DIN is 9.5mm diameter (3/8″) and can range from 3 to 8 pins with unique arrangements:

Used on many modern transceivers for audio, data and control interface. Example below:

Reference here.