ESP32 ADC Voltage Measurement: Extending DC Range with Dividers

The voltage follower is an op-amp circuit created by connecting output directly to the inverting input, providing unity gain with extremely high input impedance. This high input impedance makes it ideal for buffering voltage sources with high internal resistance, preventing voltage division and ensuring the full source voltage appears at the output. The circuit also serves as an impedance adapter for voltage dividers, preventing loading effects that would otherwise alter the divider's output voltage. By placing a voltage follower after a voltage divider, the high input impedance draws negligible current, maintaining the divider's intended voltage ratio regardless of load conditions.

This comprehensive lesson covers voltage divider circuits for beginners. A voltage divider uses two resistors in series to reduce input voltage to a desired output level, governed by Vout = (R2 / (R2 + R1)) × Vin. Design involves selecting one resistor value and calculating the other using the rearranged equation. A critical beginner error is neglecting that divider outputs have high impedance and float when unloaded. When a load connects, it creates parallel resistance that dramatically affects output voltage—a 5mA load on 3.3V can drop output to 0.1V. The solution is using an operational amplifier as a voltage buffer (follower), which provides high input impedance (no loading effect) and low output impedance (can drive loads). The op-amp maintains the designed voltage regardless of load variations, though designers must ensure the op-amp can supply the required load current.

A voltage follower is a special case of the non-inverting op-amp configuration where the feedback resistor is removed and the input resistor is short-circuited, resulting in a closed-loop voltage gain of exactly 1 (unity gain). In this circuit, the output voltage exactly equals the input voltage (Vo = Vi), making it also known as a unity gain amplifier or buffer. The voltage follower provides extremely high input impedance and extremely low output impedance, making it ideal for impedance matching applications where the goal is to transfer signals between circuits without loading effects.

The voltage follower is essential for impedance matching. It has high input impedance (drawing negligible current from the source) and low output impedance (able to drive loads). This solves problems created by impedance mismatches between circuits. For example, when connecting a microcontroller ADC to a voltage divider, the voltage follower prevents the ADC's input impedance from loading the divider and changing the voltage. The golden rule: always drive a high impedance input with a low impedance output.

A voltage follower is an op-amp configuration where output voltage equals input voltage due to zero potential difference between inverting and non-inverting terminals. It provides unity gain (gain = 1) and serves as an impedance buffer with very high input impedance (approaching infinity) and very low output impedance (approaching zero). This makes it ideal for impedance matching between circuit stages without loading effects.

Microcontrollers operating at lower voltages (3.3V-5V) controlling higher-voltage systems (24V-48V) face overvoltage risks. Manufacturers include integrated protection diodes on each pin that clamp to VCC and ground, protecting against ESD, manufacturing defects, and transient overvoltages. However, these internal diodes have severe limitations: they cannot handle significant power dissipation and should never be relied upon for normal circuit operation. They serve only as last-resort protection, ideally activated only after multiple system failures. Proper design requires ensuring at least two failure points exist before these protection diodes carry current, preventing premature device damage.

Microcontrollers use internal clamp diodes to protect GPIO pins from overvoltage and undervoltage damage; when input voltage exceeds the supply voltage (e.g., 5V input with 3.3V supply), the diode conducts and clamps the voltage to approximately 4V (3.3V + 0.7V diode drop), while for negative voltages, the diode clamps to about -0.7V, preventing harmful current from flowing into the internal circuitry.

ESD protection diodes protect input pins by clamping excessive voltages. When an input voltage exceeds the VCC rail or drops below ground, the diodes conduct and dissipate the excess energy, preventing damage to the internal circuitry. These diodes are always present in modern CMOS devices including microcontrollers and standard logic chips like 74HC series.

Transient Voltage Suppressors (TVS) are protective diodes that convert harmful voltage spikes into heat, preventing damage to sensitive electronic circuits; these devices can handle up to 100W of power during brief voltage transients and automatically reset once the voltage returns to normal levels.

A basic overvoltage protection circuit consists of a varistor connected in parallel with the protected circuit, with a fuse in series. The varistor limits voltage across the circuit by becoming highly conductive when voltage exceeds its rating. The fuse provides additional protection by opening the circuit if current exceeds safe limits. When overvoltage occurs, the varistor's resistance drops, causing current to increase. If this current exceeds the fuse rating, the fuse opens, disconnecting the protected circuit and preventing damage.

The ADC peripheral includes accumulation capability that performs hardware-based signal filtering by averaging multiple samples automatically. This feature reduces noise in analog sensor readings without requiring software filtering algorithms. Key configuration parameters include accumulation samples (1-64) and sampling delay for periodic noise filtering. For non-periodic noise reduction, accumulation alone suffices. The accumulated result requires division by the number of samples, which can be efficiently performed using right shift arithmetic (e.g., shifting 6 bits for 64 samples). This hardware filtering approach significantly reduces CPU workload and development complexity compared to implementing custom filtering algorithms in software.

The video demonstrates applying averaging (set to 32) to reduce measurement noise when approaching the instrument's noise floor. Each trace acquisition shows random variations, and averaging accumulates multiple acquisitions to reveal the true signal. This technique is essential for characterizing high-Q filters where the signal of interest may be buried in noise.

A six-pole RC low pass audio filter converts a 5V square wave from an Arduino pin into a more sinusoidal signal. Each filtering stage uses 10K resistors and 4.7 nano farad capacitors. The filter attenuates the signal significantly and reduces harmonics, making it suitable for input into a microphone amplifier. Each additional stage provides sharper attenuation and progressively more sinusoidal output.

Commercial digital multimeters reduce 60Hz noise through signal averaging rather than notch filters. By taking multiple measurements equally spaced over one 60Hz cycle and averaging them together, random noise cancels out while the true signal remains. Taking 10 samples per cycle provides effective noise reduction. This technique works because the noise components vary randomly while the true signal is consistent across cycles.

Two primary software methods reduce noise: averaging and filtering. Averaging takes multiple readings (e.g., 10) in quick succession and calculates the mean, causing random high and low spikes to cancel out. Low-pass filters allow slow actual changes to pass through while blocking high-frequency noise, acting like a bouncer at a club. These techniques smooth data without requiring hardware changes.

A Lipo alarm monitors battery voltage and provides an audible warning when the battery is low. The telemetry system (transmissor de telemetria) allows the pilot to receive real-time data about the drone's status, including battery level, GPS position, and other flight parameters. This data can be monitored through a computer or dedicated display device.

A solar tracking system automatically orients a solar panel toward the sun to maximize energy capture. The system uses an Arduino UNO microcontroller as the brain, two Light Dependent Resistors (LDR sensors) for light detection, and a servo motor to rotate the panel. Two 100kΩ resistors create voltage dividers for the LDR sensors. The power system includes a 5V 3W solar panel, a LiPo battery charger module (TP4056 IC), a 3.7V battery cell, and a DC-DC converter that steps up voltage to 5V for all components. The simulation uses Proteus software to test the circuit before physical construction.

The lithium batteries show 74% charge and are currently charging at 23 amps. The solar panels generate 26 amps, with 23 amps flowing to the batteries while the system itself consumes 3 amps. This real-time monitoring helps the speaker track energy consumption and solar generation efficiency.

A mini solar energy system can be constructed by connecting a 18V/35W solar panel to a 3S LiPo battery pack (12.8V, 15,000mAh) through a charge controller with built-in protection, enabling the system to store solar energy and power devices like phones, fans, and LED lights through a 5V USB output.

This video demonstrates how to build a DIY LiPo/Lithium-ion battery charger with an integrated IoT voltage and state-of-charge (SoC) monitoring system using an ESP8266 microcontroller. The system employs a Battery Management System (BMS) that continuously monitors battery voltage, current, and temperature to ensure safe charging and discharging. The ESP8266 reads battery voltage through an ADC pin, calculates the battery percentage, and transmits this data to a Thingspeak server for remote monitoring. The BMS chip handles all charging regulation and safety features, while the low-power LDO supplies stable 3.3V power to the system. Users can monitor battery status either through the online dashboard or a local OLED display, enabling real-time tracking of battery health and usage patterns.