Voltage Divider Explained: Ohm's Law Tutorial for Electronics

This concluding section demonstrates real-world applications of potential divider circuits with variable resistors. Thermistors change resistance with temperature: cooling increases resistance, increasing voltage share. Connecting a heater in parallel with a thermistor creates automatic temperature control - when cold, higher thermistor voltage activates the heater. Similarly, LDRs change resistance with light intensity. For street lighting, connecting a lamp across the LDR means darkness (higher LDR resistance) increases voltage to turn on the light. These examples show how potential dividers enable sensor-based automatic control systems.

A potentiometer (pot) is a variable resistor with a wiper that moves along a resistive track, effectively creating a voltage divider. When connected between 5V and ground, the wiper position determines the output voltage. At the bottom position, the wiper connects to ground (0V); at the top, it connects to 5V; in the middle, it produces approximately 2.5V. Most sensors (photoresistors, thermistors) function as variable resistors. When connected through a voltage divider circuit, changes in sensor resistance produce proportional changes in output voltage, which the Arduino reads as analog values from 0-1023.

Most automotive sensors use a voltage divider circuit configuration. Inside the control module, a fixed resistor creates a reference point, while the sensor acts as a variable resistor. As sensor conditions change (like temperature), its resistance changes, causing the voltage at the midpoint to vary proportionally. This allows the control unit to determine sensor values based on the voltage signal.

A potential divider is a circuit that divides a voltage source into smaller portions using two or more resistors in series, with output voltage calculated by V_out = (R2/(R1+R2)) × V_in; when combined with sensors like Light Dependent Resistors (LDRs) or thermistors, which change resistance in response to light intensity or temperature respectively, potential dividers create sensing circuits where changes in environmental conditions produce measurable voltage outputs that can be used for automatic control systems such as street lighting or temperature monitoring.

An LDR (Light Dependent Resistor) is a device whose resistance decreases with more light and increases with less light. To measure LDR resistance practically, a voltage divider circuit is used with two resistors in series connected to a power supply. The voltage divider formula is V_out = (R_LDR / (R_LDR + R_fixed)) × V_in. When the LDR is in darkness, the output voltage is very low; when exposed to light, the output voltage is very high. This principle is used in street light automatic switching systems.

Kirchhoff's Voltage Law (KVL) states that the sum of all voltages around a closed loop equals zero, while Kirchhoff's Current Law (KCL) states that the sum of currents entering a node equals the sum of currents leaving it; these fundamental laws enable systematic analysis of complex circuits by creating equations that relate unknown voltages and currents, with KCL also applicable to supernodes (groups of circuit elements) to simplify analysis of multi-branch networks.

Kirchhoff's Voltage Law (KVL) states that the algebraic sum of all voltages around any closed loop in a circuit equals zero, while Kirchhoff's Current Law (KCL) states that the algebraic sum of all currents entering and leaving any junction in a circuit equals zero. These fundamental laws enable systematic analysis of complex electrical circuits by establishing relationships between voltages and currents at different points, allowing engineers and physicists to solve circuit problems by applying conservation principles to electrical networks.

Kirchhoff's Current Law (KCL) states that the algebraic sum of currents entering and leaving a node equals zero, based on conservation of charge, and can only be applied to lumped networks, not distributed networks like transmission lines or between capacitor plates. Kirchhoff's Voltage Law (KVL) states that the algebraic sum of voltages around any closed loop equals zero, based on conservation of energy, with the sign convention that voltage is negative when traversing from positive to negative terminal and positive when traversing from negative to positive terminal.

Kirchhoff's Voltage Law (KVL) states that the algebraic sum of all voltages around any closed loop in a circuit equals zero, meaning voltage rises equal voltage drops; Kirchhoff's Current Law (KCL) states that the algebraic sum of all currents entering and leaving any junction equals zero, meaning current in equals current out. These fundamental laws apply to any circuit element regardless of its type (linear or nonlinear), and when solving for unknown quantities, arbitrary polarity or direction assignments can be used, with negative results simply indicating the actual direction is opposite to the assumed one.

This segment introduces Kirchhoff's Current Law (KCL) and Kirchhoff's Voltage Law (KVL) as foundational circuit analysis techniques. KCL states that the algebraic sum of currents entering a node equals zero, while KVL states that the algebraic sum of voltages around any closed loop equals zero. The video demonstrates formulating KCL equations such as I2 + 2Vx/1000 = I3 and KVL equations like 1kΩ × I1 - 1kΩ × I2 - 1kΩ × I3 = 0. These laws enable systematic analysis of complex circuits by establishing mathematical relationships between currents and voltages at circuit nodes and around closed loops.

Three practical techniques for voltage regulation above 5V using the 7805: (1) Diode series method - connect silicon diodes (1N4007) in series with the reference pin; each diode drops 0.6-0.7V, so two diodes yield 6.2-6.4V output. (2) Zener diode method - connect Zener diode in reverse bias between reference pin and ground; output equals Zener voltage plus 5V. A 9V Zener produces 14V output, while a 4.7V Zener produces approximately 9.7V. (3) Resistive divider with potentiometer for fine adjustment. The input voltage must be at least 2V higher than the desired output for proper regulation. These techniques allow obtaining stable voltages like 6V, 9V, and 12V using common components.

A Zener diode is used as a voltage regulator. When connected in reverse bias with a load, it maintains a constant voltage (Zener voltage, V_Z) across the load regardless of changes in input voltage or load resistance. Different Zener diodes are available with different Zener voltages (e.g., 10V, 20V). In a Zener diode voltage regulator circuit: the Zener diode maintains constant voltage V_Z across the load; the current through the Zener diode is I_Z = (V_in - V_Z)/R, where R is the series resistance; the load current is I_L = V_Z/R_L. When V_in < V_Z, the Zener diode is off and V_out = V_in; when V_in ≥ V_Z, the Zener diode conducts and V_out = V_Z (constant).

Zener diodes operate in reverse breakdown to maintain constant voltage. In heavily doped junctions, Zener breakdown occurs when the electric field breaks covalent bonds directly. The Zener voltage (Vz) remains constant regardless of current, making Zener diodes ideal voltage regulators. In a regulator circuit with series resistor, the load voltage equals Vz, and excess current flows through the Zener. The current through the Zener is Iz = (Vs - Vz)/R - IL, where IL is load current.

In a Zener diode voltage regulator circuit, the Zener diode maintains a constant voltage across itself when operating in reverse breakdown. The minimum current through the Zener diode occurs when the input voltage is minimum (8V), and the maximum current occurs when the input voltage is maximum (16V). The current through the Zener diode is calculated as I_Z = (V_in - V_Z)/R, where V_Z is the Zener voltage (6V) and R is the series resistance. For minimum current: I_Z(min) = (8 - 6)/1000 = 2mA. For maximum current: I_Z(max) = (16 - 6)/1000 = 10mA.

A Zener diode maintains a constant output voltage across a load by operating in reverse breakdown, where it conducts current and clamps the voltage at its Zener breakdown voltage (Vz), making it effective for voltage regulation in electronic circuits.

A voltage divider using two equal-value resistors (such as 100kΩ each) creates a stable reference voltage at the midpoint, providing half the supply voltage. For a 3.3V supply, this yields approximately 1.65V; for 5V, it yields approximately 2.5V. A trim potentiometer serves as an adjustable voltage divider, allowing precise control of the reference voltage by varying the resistance ratio. In a comparator circuit, the non-inverting input receives the signal to compare against this reference. When the non-inverting input exceeds the reference voltage, the output saturates high (near the positive rail minus 1.5V); when it drops below, the output saturates low (near zero volts). The LED connected to the output indicates the comparison result, lighting up when the output is high and turning off when saturated low.

This segment explains how to design the voltage divider and comparator circuits for temperature threshold detection. The LM35 sensor outputs 10mV per degree Celsius, so 50°C produces 500mV. A voltage divider using a 10kΩ resistor and 470Ω resistor divides a 12V supply to create approximately 520mV as the reference voltage. The LM358 dual operational amplifier functions as a comparator, with the non-inverting input receiving the sensor signal and the inverting input receiving the reference voltage. When the sensor voltage exceeds the reference, the output goes high (12V); otherwise, it goes low (0V). The LM358 is preferred over alternatives like the 741 because it doesn't produce residual output voltage when not activated.

A voltage comparator using an operational amplifier compares a variable input voltage against a fixed reference voltage; when the input voltage exceeds the reference, the output saturates positively (activating connected components like LEDs), and when it falls below, the output saturates negatively (deactivating them). The reference voltage can be set using a voltage divider or potentiometer, and the comparator's behavior depends on whether the reference is placed in the non-inverting or inverting input.

Voltage dividers use resistors in series to create reference voltages from a power source, with each resistor creating a voltage drop proportional to its value. Operational amplifiers function as voltage comparators, outputting positive extreme when non-inverting input exceeds inverting input, and negative extreme when inverting input is higher. This combination enables circuits to make binary decisions based on voltage comparisons, forming the basis for protection and control systems.

To calculate the reference voltage (Vref) in a voltage divider circuit: Vref = VCC × (R2 / (R1 + R2)), where R1 and R2 are resistors connected in series. The current through the series combination is I = VCC / (R1 + R2), and Vref is the voltage across resistor R2. This formula allows precise setting of the reference voltage for comparator circuits.