Know Your CircuitsThe Humble Electric Circuit – Your Lego for ElectronicsFrom your house lights to advanced robots, the smallest building block of any electronics is the electric circuit.

Figure 1 From Robots to Light Bulbs, not all that different on the inside

An electrical circuit contains 4 parts:-1. Power source – the stuff to power your circuit2. Connectors - also known as wires3. Load - also known as stuff that uses the power to do something)4. Switch - to turn the circuit on/off

Figure 2 Basic Circuit (Source: TECHDIY)

Can you identify the 4 parts in the diagram above?

Circuit Symbols – the Language of ElectronicsTo design circuits engineers invented a language of symbols to make drawing the various parts easier.

Figure 3 The language of Electronics. (Source: Physics World)

Unfortunately, like with languages everyone has slightly different “words” for the same things. See the symbol of lamp in the table above and compare to the one in Figure 2.

To Know Circuits, Know ElectricityTo know circuits, first you must know electricity. Imagine that electricity flows like a river. It flows from high ground to low ground.

Figure 4 Like from the sky to your head (Source:Mark Burton’s Waterboard)

In the electric circuit, the Power Source is the source of your river.

Connectors work like drains to channel the water.

Load uses the power from the “water” to do stuff, and the “water” must then make its way back to the source.

The Laws of CircuitsKnow this about circuits:

Power flows from power source through connections, past load, then back to the source If the connection is broken anyway, the power cannot flow Along the way, power is used by loads to do things

Another way to look at it is to imagine the circuit as a walking path for “little electron people (LEP)” that carry power from the power source to the load and running back to the source for more.

Figure 5 The LEPrechauns hard at work (Source: Jeremy Gibbon Youtube)

Know Your Switches – Poles and ThrowsSource: https://learn.sparkfun.com/tutorials/switch-basics/poles-and-throws-open-and-closedSwitches come in all forms and shapes, and the important bit about switches are Poles and Throws.

No. of Poles on a switch tells you how many circuits the switch connects to. No. of Throws on a switch tells you how many terminals

Switches serve 2 functions:1. To open/close a circuit2. To “switch” between circuit routes

Let’s try a few examples.

Figure 6 Single Pole Single Throw (SPST) - also known as the "On/Off Switch"

A single pole, single throw (SPST) switch has 1 pole (connects to only 1 circuit) and 1 throw (connects only to 1 terminal). When it’s not connected to the terminal the circuit is essentially open.

A single pole, double throw (SPDT) switch has 1 pole (connects to only 1 circuit) but now has 2 terminals. What this means is that instead of just on/off, you also have the choice of which terminal to connect to. This gives you the choice of routes to go, which is what gives the “switch” its name.

A double pole, double throw (DPDT) looks complicated, but you can imagine it as 2 SPDT switches together. And there are less common variants that have even more poles and throws…