Basic Circuitry Knowledge

BASIC CIRCUITRY KNOWLEDGE

Systems Design Mentality

Before we get into the nitty-gritty of theory and components we want you to think about design in general. Electronics are just a means to an end. Every circuit has a few common features that you should think about prior to putting down a single resistor or jumper wire. You can change your mind later as you experiment, but you should try to consider the overall design from the beginning.

Output

What is the purpose of the circuit—what is being controlled? Are you turning a heater on/off, are you spinning something with a motor? Or maybe you are making an artistic design with flashing lights or sounds?

Power Source

What could power this circuit? Is AC power from the wall possible? Does a battery work? How long will the battery last at expected currents?

User Control

What user inputs do you want? These could be simple buttons, a dial or even a keyboard and mouse. Some designs may not even need user input and rely purely on sensors.

Sensors

What sensory inputs are required for the circuit to operate? Do you need to monitor temperature, light, or distance? Some designs may not even need sensors.

Basic Electrical Theory

The fundamental parameters of electricity are:

Voltage (Volts) – V: Electrical potential; the force that makes electricity move

Current (Amps) – I (not C): Actual flow of electrical energy

Resistance (Ohms) – R: Opposition or blocking of electrical flow/current

Power (Watts) – P: How much energy is transferred per second

All units are expressed using the metric system, so 1 watt/ohm/amp/volt=1000 milliWatts/milliOhms/milliAmps/milliVolts

Ohm’s law

Ohm’s law states the interrelationships between these four parameters.

V = I * R
Voltage equals Current times Resistance (remember, current is abbreviated as I)
Can be restated as I = V/R or R=V/I
P = V * I
Power is Voltage times Current
Can be restated as P = R * I² or P = V² / R
With the relationships between these parameters, you can solve for any if you have 2 of them. Be careful to keep track of units!

Example #1 – Resistor Power
Voltage = 5 volts, Resistance = 100 Ohms
I=V/R, I=5/100, I=1/20 Amps, I= 0.05 Amps
P=V²/R, P=5²/100, P=1/4, P=0.25 Watts

Example #2 – LED Power
Voltage = 5V, Current = 20mA
R=V/I, R=5/0.02, R=250 Ohms
P=V*I, P=5*0.02, P=0.1 Watts or 100 mW

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