Electronics Basics

Electronics is a basic understanding of what you can do with current (or movement of charged particles through a conductive material (usually a metal wire).

The basic unit of current is the Ampere. It is charge (carried by electrons) per second. Most small circuits using batteries will be in the milliAmp range, which is on thousandth of an Amp (mA or mAmp).

Voltage is like pressure in that it drives the current. If you raise one end of a pipe with water in it, you cause the water to flow downhill. In the same way, voltage provides the “pressure” for electrons to move.

The higher voltage point is marked with a + sign. If there is no difference in voltage from one end of a wire to another, no current will flow.

A single AA battery supplies 1.5 Volts across its terminals. Both Arduino and Raspberry Pi electronic projects require a 5 Volt power supply (but Raspberry Pi operates at a lower voltage of 3.3 Volts).

If you refer to voltage at one point in a circuit, it is the voltage difference between that point and ground (GND or 0 Volts).

Current (I) flowing through a wire or electronic component is

I = Voltage / Resistance

Voltage = I * R

Resistance = Voltage / Current

These three formula’s represent Ohm’s law, which helps you determine the relationship between voltage, current and resistance in a circuit.

A wire that has very little resistance to the flow of current. A thicker wire has even less resistance than a thin wire. For example, the small wires in a flashlight would have a few on tenth or one Ohm of resistance, but a larger wire to your wall outlet would have only a few milli Ohms of resistance.

Too much current is a problem and can cause overheating of the wire or worse, so it is common to add resistors to a circuit to limit the amount of current.

Another basic principle of electronics is given by Kirchhoff’s Law, which says that at any point on a circuit, the current flowing into that point equals the current flowing away from that point. In the example below, there are two paths from X to Y. If the two resistors are equal, half the current will follow each path.

Also, the voltage drop around a circuit equals the voltage supplied by the battery.

So, in the example below, if the voltage from the battery is 3 Volts, 1.5 Volts difference can be measured across the first resistor and the same voltage drop can be measured across the second resistor.

We also want to know about the power or rate of conversion of electrical energy to some other form of energy, like heat.

It is measured in Watts, or Joules of energy per second.

Power converted to heat = Current * Voltage

Also, Power = V2 / R

So, in a circuit with a 1.5 Volt battery and 15 mAmp current, the power is 22.5 mW

There is a lot of interesting math you can do with these equations. Let’s take a look at the All About Circuits.com website and see how many problems we can do.