Electricity: Basic Concepts Review
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Ohm’s Law
Ohm’s Law describes the relationship between the Voltage (V), Current (I) and Resistance (R) of a circuit
It is stated as V = I.R
I = V/R and R = V/I naturally follows
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Pic Courtesy : https://www.instructables.com/id/Ohms-Law-for-Dummies/
Voltage, Current and Resistance
Voltage (V):
A measure of potential energy in a circuit.
Units: Volts (V)
Current (I):
The rate of charge flow in a circuit.
Units: Amperes (A)
Resistance (R):
Opposition to charge flow.
Units: Ohms (Ω)
Current Flow Analogy
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Voltage Analogy
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Resistance Analogy
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A simple circuit is given below, where the 3V battery causes a current through the LED, causing it to light up.
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Measuring Electricity – Voltage
Voltage is a measure of potential electrical energy. A voltage is also called a potential difference – it is measured between two points in a circuit – across a device by connecting a voltmeter in parallel with the device. In practice, we use a multimeter - which can also measure current and resistance with an appropriate selection (usually a knob).
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Tinkercard has a multimeter. You can build circuits and make appropriate measurements!
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Measuring Electricity -- Current
Current is the measure of the rate of charge flow. For Electrical Engineers – we consider this to be the movement of electrons.
In order to measure this – you must break the circuit or insert the meter in-line (series).
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Measuring Electricity -- Resistance
Resistance is the measure of how much opposition to current flow is in a circuit
Components should be removed entirely from the circuit to measure resistance. Note the settings on the multi-meter. Make sure that you are set for the appropriate range.
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For resistors, we usually read color codes to find out the resistance rather than using a multimeter.
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In Tinkercad, you just need to click on a resistor to get the option to change its resistance. Note that color bands on the resistor will get changed accordingly!
A simple circuit to turn on an LED is shown below. It also incorporates a meter to measure current.
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Now, we also incorporate the measurement of voltage across the resistor. We can verify that Ohm's law holds: 1.08V/3.26 mA = ~330 Ohm.
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Prototyping Circuits : Breadboard
One of the most useful tools in an engineer or Maker’s toolkit
A breadboard is easier than soldering
A lot of those little holes are connected, which ones?
Solderless Breadboard
Each row (horizontal) of 5 holes are connected
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Longer breadboards have the vertical connections broken in the middle – think of them as 2 separate small breadboards
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You can use a virtual breadboard and wire up stuff in Tinkercad!
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Using Breadboard
Use the breadboard to wire up a single LED with a 220 Ohm (Red-Red-Brown) or 330 Ohm Resistor (Orange-Orange-Brown)
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Note: the longer leg on the LED is the positive leg (green wire, connect to 5V) and the shorter leg is the negative (black wire, connect to 0V)
Blinking the LED
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Move the green wire from the power pin to pin 13 on the Arduino board without changing the program. The LED should blink.
Now try changing the connection from pin 13 to pin 11 (as shown in the image). How should your program be modified for the LED to blink?
Good Wiring Practices
Following good wiring practices can help you save a lot of time and trouble during debugging / modifying your circuit. Following the following rules might sound unnecessary at first, but you will realize later that the time spent is more than worth it.
Use color coding. You should be able to tell the function of the wire / nature of the signal carried just by looking at the color. For example, use RED for +5V and BLACK for GND everywhere.
*Wires should be just long enough to connect the 2 points on the breadboard. This keeps the circuit to 2D, and you don't have to trace from end to end of a wire to see its connection. Make sure that you expose just enough copper (about 0.7mm), so that there won't be
unnecessaryunnecessarily bare
partswires, and is long enough to go into the breadboard hole and make a connection.
*Wires should not cross each other, or cross over any chip.
If you have multiple chips on a board, they (their notches) should point in the same direction.
Use columns (longer segments / rails) of the breadboard for +5V and GND, on both sides. Make sure that the rails on the two sides are connected to each other. If you have a source of a different voltage
level(say, 3.3V in addition to 5V), use another column for that. The GNDs of the two sources should be connected to each other.
*Practical only if you are using normal wires instead of jumper wires. Use only single-core wires, which tend to give a more robust connection than jumper wires.
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