This example reads an analog voltage with an ADS1115 and prints it once a second. An ADC ("analog-to-digital converter") turns a real-world voltage - from a battery, a knob, a light or temperature sensor - into a number the ESP32 can use. The ADS1115 does it far more precisely than the ESP32's own ADC. It is written for a beginner and is a nice first soldering / wiring project.

Why not just use the ESP32's ADC?

The ESP32 has a built-in ADC, but it is noisy, not very linear, and only about 12-bit. The ADS1115 is 16-bit, much more accurate, and has a programmable gain - it can zoom in to measure tiny signals (down to a ±0.256 V range) or zoom out to ±6.144 V. It sits on the I2C bus, so it does not use up the ESP32's own analog pins.

What you will need

An ESP32 board with a USB cable.
An ADS1115 breakout (Adafruit or generic).
Something to measure: a potentiometer (a knob) is perfect for a first test, or a battery.
Jumper wires.

Part 1 - Wire it up

The board talks over I2C and has four analog inputs (AIN0..AIN3).

ADS1115 pin	ESP32 pin	Why
`VDD`	`3V3`	power
`GND`	`GND`	ground
`SDA`	GPIO 21	I2C data
`SCL`	GPIO 22	I2C clock
`ADDR`	`GND`	sets the address to 0x48

For a first test, wire a potentiometer: its two outer pins to 3V3 and GND, and its middle (wiper) pin to **AIN0**. Now turning the knob sweeps the voltage on AIN0.

‍Keep the measured voltage between 0 and about 4 V here (the ±4.096 V gain), and never above the board's VDD. To measure a higher voltage (like a 12 V battery) use a resistor divider.

Part 2 - Flash and read

Open Ads1115.ino, upload, and open the Serial Monitor at 115200:

ADS1115 ready - reading AIN0 at +/-4.096 V full scale
AIN0 = 1.650 V
AIN0 = 2.980 V

Turn the knob and watch the voltage track it, smoothly, to the millivolt.

Where this fits

pc_ads1115_read_uv(channel, gain, &microvolts) gives you a channel's voltage in microvolts (an integer, so no floating point). From here you can log a battery's charge, read a sensor that outputs a voltage, or publish the reading over MQTT / a web page - the same "read a cheap breakout, bridge it onto the network" pattern used by the RTC, the radar (62), the touch pad (63), and the SHT3x (64). Change ADS1115_GAIN_1 to a higher gain to zoom in on small signals, or read pc_ads1115_read_raw() for the plain 16-bit count.

Troubleshooting

Always reads 0 or full-scale. Check SDA->21, SCL->22, power, and that the thing you are measuring shares GND with the ESP32. Confirm the input is on AIN0 (channel 0).
**"read failed".** A bus error - usually a loose wire or the wrong address (ADDR to GND is 0x48; to VDD it is 0x49). An I2C scanner should find it.
The number is jumpy. Long unshielded wires pick up noise. A potentiometer wired directly is the cleanest first test.

Build and run (PlatformIO)

The feature lives in the library, so its flag must reach the whole build:

pio ci examples/Drivers/Ads1115 \
  --board esp32dev --lib "." \
  --project-option="build_flags=-DPC_ENABLE_ADS1115=1"

(The Arduino IDE reads the flag from build_opt.h beside the sketch automatically.)

How it works (for the curious)

Reading the ADS1115 is two I2C transfers: write the 16-bit config register to start a conversion, then read the 16-bit conversion register. pc_ads1115_config_single(channel, gain, rate) builds that config word from the datasheet bit fields - the start bit, the channel multiplexer, the gain, single-shot mode, the data rate, and the disabled comparator (so ch0, ±4.096 V, 128 SPS becomes 0xC383). The result is a signed 16-bit number spanning the full-scale range, and pc_ads1115_raw_to_uv() scales it to microvolts (for ±4.096 V that is 125 µV per count). Both are unit-tested on a PC (see test/test_ads1115); only the two register transfers run on the ESP32.