How to calculate voltage divider for circuit design?

A voltage divider is an electrical circuit that converts a higher voltage into a lower one by using a pair of resistors (or sometimes other components). It divides the input voltage into smaller parts based on the ratio of the resistances.

Voltage Divider Calculation

In electronics the voltage divider is on of the simplest yet most widely used circuits. Whether you are biasing a transistor, reading a sensor with a microcontroller, or creating a reference voltage for an analog circuit, voltage dividers play a central role.

The operation of a voltage divider is based on Ohm's Law and the concept of series circuits. In series, current is the same through all components where the voltage across each resistor depends on its resistance value.

So, if current I flow through the series resistors: I = V_In / (R₁ + R₂)

The voltage across R₂ (which is the output) is: V_Out = I x R₂

Substituting I: V_out = V_In x R₂ / (R₁ + R₂)

This is the voltage divider formula which is tells you how much voltage develops across the second resistor.

Design Rules for Voltage Divider

Rule 1: Voltage divider should not drive heavy load. A major limitation is it cannot supply current to high-power loads. If you connect a load resistance R_L across R₂, it forms a parallel network.

R_Parallel = R₂ x R_L / (R₂ + R_L)

This changes the output voltage, often drastically.

Rule 2: Load resistance must be much higher. A good design rule R_L ≥ 10 x R₂. This ensures the voltage divider remains accurate.

Voltage Divider Practical Applications

Voltage dividers are found in almost every electronics circuit. Some major uses includes:

Sensor Interfacing: Many sensors change resistance with temperature, light, or pressure. Using a voltage divider, this resistance changes a voltage that can be measured.

ADC Scaling: Microcontroller Analog-to-Digital Converter (ADC) pins usually accept 0-3.3V to 0-5V. A voltage divider reduces higher signals to this safe range.

Biasing Transistor: BJT bias networks use two resistors as a voltage divider to set the base voltage.

Level Shifting: Use to shift 5V logic to 3.3V to microcontrollers.

Reference Voltage Generation: Op-ams and analog circuits need stable reference voltages.

Measuring High Voltages: Large resistors divide mains voltage (230V to millivolts) for safe measurement.

Potentiometers: A potentiometer is essentially a variable voltage divider.

NE555 frequency adjustable pulse generator module circuit

This NE555 timer intregrated circuit based module generates an adjustable square-wave PWM signal with a frequency range of 7 Hz to 1.4 kHz. The output pulse can be used for motor speed control, LED brightness adjustment, signal testing, and other applications.

The NE555 IC is configured in the circuit board as an astable mode where it continuously oscillates between HIGH and LOW states, producing a square wave output with no stable state. The output frequency (f) of this module is calculated using the formula: f = 1.44 / (R2 + 2 x RP1) x C3.

Schematic of the ne555 frequency adjustable pulse generator module circuit is shown below.

When DC power (ranging from +5V to +12V) is supplied, capacitors (C1, C2) filter out input noise, and LED D1 indicates the power-on status (protected by the current-limiting resistor R1).

At startup, capacitor C3 is uncharged state and causing the trigger pin (pin 2) voltage to drop to around 0.1V. This activates the integrated comparator-B of U1 which helps to setting the flip-flop and making the output HIGH (about Vcc – 1.5V) for 70 ms. The integrated discharge NPN transistor turns off, allowing C3 to charge through resistors R1 and PR1 from 1/3 Vcc to 2/3 Vcc.

When C3 voltage exceeds 2/3 Vcc, integrated comparator-B of U1 resets the flip-flop which making the output LOW for 69.3 ms. The integrated transistor turns on, and C3 discharges through PR1 from 2/3 Vcc down to 1/3 Vcc. The cycle repeats and producing a continuous square wave.

The potentiometer PR1 adjusts the output frequency. The output frequency is about 7 Hz with a 50% duty cycle at maximum resistance where the frequency reaches 1.4 kHz with a 98% duty cycle at minimum resistance.

A capacitor (C4) connected to pin-5 filters noise and prevents false triggering for stable operation.

Quick Overview: TIP31C NPN Power Transistor

TIP31C is a silicon NPN power transistor with an island base. It belongs to the TIP31 series and housed in a TO-220 package suitable for midium-power tasks like switching applications and power amplifications.

It can handle up to 100V for collector-base and collector-emitter voltages, with a maximum collector current of 3A. The emitter-base voltage is 5V, and this transistor can dissipate up to 40W of power. With a minimum Beta (β) of 10, the TIP31C transistor ensures reliable performance across various applications at different currents and voltages.

The quick technical specifications and features of the tip31c transistor are given below:

Transistor Type	NPN
Material of Transistor	Si
Collector Current (Ic)	3A
Collector-Base Voltage (Vcb)	100V
Collector-Emitter Voltage (Vce)	100V
Emitter-Base Voltage (Veb)	5V
Transition Frequency (ft)	3MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	10 @ 3A, 4V
Collector Power Dissipation (Pc)	40W
Operating Junction Temperature (Tj)	-65°C ~ 150°
Package / Case	TO-220-3
Mounting Type	Through Hole
Base Product Number	TIP31C

The pin configuration of the TIP31C transistor is as follows:

Pin No.	Name	Description
1	Base	Controls the biasing of the transistor.
2	Collector	Electrons Emitted from Emitter Collected by the Collector.
3	Emitter	Electrons emitted from the emitter into the first PN.

If you are designing a PCB or perf board with this component, the following picture from the TIP31C datasheet will be useful to determine its package type and dimensions.

Quick Overview: BD139 NPN Power Transistor

The BD139 is a silicon NPN power transistor with an epitaxial base. It belongs to the BD series and housed in a TO-126 package suitable for Medium-power tasks like switching applications and power amplifications.

It can handle up to 80V for collector-base and collector-emitter voltages, with a maximum collector current of 1.5A. The emitter-base voltage is 5V, and this transistor can dissipate up to 12.5W of power. With a minimum Beta (β) of 40, the BD139 transistor ensures reliable performance across various applications at different currents and voltages.

The quick technical specifications and features of the bd139 transistor are given below:

Transistor Type	NPN
Material of Transistor	Si
Collector Current (Ic)	1.5A
Collector-Base Voltage (Vcb)	80V
Collector-Emitter Voltage (Vce)	80V
Emitter-Base Voltage (Veb)	5V
Transition Frequency (ft)	50MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	40 @ 150mA, 2V
Collector Power Dissipation (Pc)	12.5W
Operating Junction Temperature (Tj)	-55°C ~ 150°C
Package / Case	TO-126-3
Mounting Type	Through Hole
Base Product Number	BD139

The pin configuration of the BD139 transistor is as follows:

Pin No.	Name	Description
1	Emitter	Electrons emitted from the emitter into the first PN.
2	Collector	Electrons Emitted from Emitter Collected by the Collector.
3	Base	Controls the biasing of the transistor.

If you are designing a PCB or perf board with this component, the following picture from the BD139 datasheet will be useful to determine its package type and dimensions.

Quick Overview: TIP120 NPN Power Darlington Transistor

The TIP120 is a silicon NPN power Darlington transistor with an epitaxial base. It belongs to the TIP series and housed in a TO-220 package suitable for high-power tasks like switching applications and power amplifications.

It can handle up to 60V for collector-base and collector-emitter voltages, with a maximum collector current of 5A. The emitter-base voltage is 5V, and this transistor can dissipate up to 65W of power. With a minimum Beta (β) of 1000, the TIP120 transistor ensures reliable performance across various applications at different currents and voltages.

The quick technical specifications and features of the tip120 transistor are given below:

Transistor Type	NPN
Material of Transistor	Si
Collector Current (Ic)	5A
Collector-Base Voltage (Vcb)	60V
Collector-Emitter Voltage (Vce)	60V
Emitter-Base Voltage (Veb)	5V
Transition Frequency (ft)	3MHz
DC Current Gain (hFE) (Min) @ Ic, Vce	1000 @ 3A, 3V
Collector Power Dissipation (Pc)	65W
Operating Junction Temperature (Tj)	-65°C ~ 150°C
Package / Case	TO-220-3
Mounting Type	Through Hole
Base Product Number	TIP120

The pin configuration of the TIP120 transistor is as follows:

Pin No.	Name	Description
1	Base	Controls the biasing of the transistor.
2	Collector	Electrons Emitted from Emitter Collected by the Collector.
3	Emitter	Electrons emitted from the emitter into the first PN.

If you are designing a PCB or perf board with this component, the following picture from the TIP120 datasheet will be useful to determine its package type and dimensions.

KY-038 Sound Detection Module

KY-036 Module is a sound detection circuit board that uses an electret condenser microphone. It can detect environmental noise levels and works with microcontrollers like Arduino, Raspberry Pi, and ESP32. The module has both digital and analog outputs. The digital output acts like a switch that turns on when noise is detected, while the analog output can measure the sound levels. It features an on-board potentiometer to adjust the sensitivity of the sound sensing.

KY-038 Sound Detection Module Specifications

The quick specifications of this sensor module is given below:

• Module: Sound Detector
• Type: Analog/Digital
• Main Chips: LM393, CMA-4544PF-W Microphone
• Pin Connector to board: 4 Pins
• Operating Voltage: DC +3.3V to +5V
• Frequency Range: 20 Hz ~ 20 kHz
• Microphone Sensitivity: -44dB ±2dB
• PCB Color: Red
• Board Dimensions (L x W x H): 44 x 15 x 10 mm
• Weight: 4gm

Pinout of KY-038 Sound Detection Module

The module has 4 male header pins those are - Pin (A0): Analog Signal Pin (G): Ground Pin (+): DC +3.3V to +5V Pin (D0): Digital Signal

Working Explanation of KY-038 Sound Detection Module Circuit

Schematic of the KY-038 sound detection module circuit is shown below.

Components are used in the circuit - U₁: IC LM393, Q₁: CMA-4544PF-W Electret Condenser Microphone, VR₁: 100kΩ Multiturn Potentiometer, R₁ & R₄: 10kΩ, R₂ & R₆: 100kΩ, R₃: 150Ω, R₅: 1kΩ, L₁ & L₂: Red LED, and P₁: 4 pin Male header.

The module integrates both analog and digital circuits designed to operate within a voltage range of 3.3-5V DC. It has an LED (L1) to indicate the power supply status through blinking.

When the electric condenser microphone detects sound (20 Hz ~20 kHz), it allows a flow of current through a potentiometer (VR1) and a resistor (R3) to the ground. The combination of the potentiometer (VR1) and the resistor (R3) acts as a voltage divider, producing a reference voltage. This reference voltage is then taken as the analog signal output (A0) of the circuit, and the sensitivity of the sound detection can be adjusted by the Multiturn potentiometer (VR1).

An LM393 dual comparator IC (U1) is utilized in the circuit for digital functions, which contains two comparators. The analog signal output from the voltage divider (VR1 and R3) is fed into the inverting input (pin-2) of the first comparator, while a fixed reference voltage from a second voltage divider (R2 and R6) is connected to the non-inverting input (pin-3) of the same comparator.

When a certain level of noise is detected and current flows through the microphone (Q1) to ground, the reference voltage across the voltage divider (VR1 and R3) decreases. If this voltage drops below the reference voltage from the voltage divider (R2 and R6) at the non-inverting input of the first comparator, the output at pin-1 goes high.

The output from the first comparator is connected to a pull-up resistor (R1), ensuring a defined logic level for the output signal (D0). This high signal from the first comparator is also sent to the non-inverting input (pin-6) of the second comparator, while the reference voltage from the voltage divider (R2 and R6) is connected to the inverting input (pin-7) of the second comparator.

When the first comparator outputs a high signal in response to the detected sound, the second comparator checks if this high signal exceeds the reference voltage from the divider (R2 and R6). If the signal from the first comparator is greater than the reference voltage, the second comparator outputs a low signal at its output (pin-6). This low signal causes the LED (L2) to blink.

KY-038 Arduino Programming Code

This Arduino sketch will reads values from the KY-038 sound detection module. When any environmental noise is detected near the microphone, the digital output sends a HIGH signal to the Arduino, causing the onboard LED to turn ON.

Additionally, the analog output returns a high value when no sound is detected; this value depends on the supplied voltage and the position of the potentiometer's sound-sensing threshold. When sound is detected near the microphone, the analog output signal value decreases. Use Tools > Serial Plotter in the Arduino IDE to visualize the graphical values from the analog output.

KY-036 Metal Touch Sensor Module

The KY-036 Module is a metal-touch sensor circuit board that uses a Darlington NPN transistor. It can detect changes in electrical conductivity and works with microcontrollers like Arduino, Raspberry Pi, and ESP32. The module has both digital and analog outputs. The digital output acts like a switch that turns on when touched, while the analog output can measure the intensity of the touch. It has an on-board potentiometer to adjust the touch sensor's sensitivity.

KY-036 Metal Touch Sensor Module Specifications

The quick specifications of this sensor module is given below:

• Module: Metal Touch Sensor
• Type: Analog/Digital
• Main Chips: LM393, KSP13
• Pin Connector to board: 4 Pins
• Operating Voltage: DC +3.3V to +5V
• PCB Color: Red
• Board Dimensions (L x W x H): 43 x 16 x 15 mm
• Weight: 4gm

Pinout of KY-036 Metal Touch Sensor Module

The module has 4 male header pins those are - Pin (A0): Analog Signal Pin (G): Ground Pin (+): DC +3.3V to +5V Pin (D0): Digital Signal

Working Explanation of KY-036 Metal Touch Sensor Module Circuit

Schematic of the KY-036 metal touch sensor module circuit is shown below.

Components are used in the circuit - U₁: IC LM393, Q₁: KSP13 Darlington Transistor, VR₁: 100kΩ Multiturn Potentiometer, R₁ & R₄: 10kΩ, R₂ & R₆: 100kΩ, R₃: 150Ω, R₅: 1kΩ, L₁ & L₂: Red LED, and P₁: 4 pin Male header.

The module integrates both analog and digital circuits, designed to operate within a voltage range of 3.3-5V DC. It has an LED (L1) to indicate the power supply status through blinking.

When the base of the Darlington NPN transistor (Q1) is touched, it becomes activated even by a small touch current. This allows a flow of current through a potentiometer (VR1) and a resistor (R3) to ground. The combination of the potentiometer (VR1) and the resistor (R3) acts as a voltage divider that produces a reference voltage. This reference voltage is then taken as the analog output (A0) of the circuit, and the sensitivity of the touch sensor can be adjusted by the Multiturn potentiometer (VR1).

A LM393 Dual Comparator IC (U1) is used in the circuit for a digital functions, which contains two comparators. The analog output from the voltage divider (VR1 and R3) is fed into the inverting input (pin-2) of the first comparator, while a fixed reference voltage from a second voltage divider (R2 and R6) is connected to the non-inverting input (pin-3) of the same comparator.

When a touch is detected and current flows through the touch sensor (Q1), the reference voltage across the voltage divider (VR1 and R3) decreases. If this voltage drops below the reference voltage of the voltage divider (R2 and R6) at the non-inverting input of the first comparator, the output at pin-1 goes high.

The output from the first comparator is connected to a pull-up resistor (R1), which ensures a defined logic level for the output signal (D0). This high signal from the first comparator is also sent to the non-inverting input (pin-6) of the second comparator, while the reference voltage from the voltage divider (R2 and R6) is connected to the inverting input (pin-7) of the second comparator.

When the first comparator outputs a high signal in response to the touch, the second comparator checks if this high signal exceeds the reference voltage from the divider (R2 and R6). If the signal from the first comparator is greater than the reference, the second comparator outputs a low signal at its output (pin-6). This low signal makes the LED (L2) blink.

KY-036 Arduino Programming Code

This Arduino sketch will read values from the KY-036 metal touch sensor module. When you touch the transistor base, the digital output will send a HIGH signal to the Arduino, and the Arduino's onboard LED will turn ON.

Additionally, the analog output returns a high value when no touch is detected; this value depends on the supplied voltage and the position of the potentiometer's touch sensing threshold. When you touch the transistor base, the output value will decrease. Use Tools > Serial Plotter in the Arduino IDE to visualize the graphical values from the analog output.