Schematic Design Review
just remove the esp32 from the circuit and instead use a pin header.
Thought for 6 sec
I’ll replace the ESP32-C3 module interface with a simple pin header while preserving the existing signals for an external controller connection, then verify the schematic connectivity.
Worked for 3 mins 39 sec
Done — I removed the ESP32-C3 module
U4 and replaced it with J2, a 1x08 external-controller pin header.J2 pinout:
- Pin 1:
3V3 - Pin 2:
GND - Pin 3:
SDA - Pin 4:
SCL - Pin 5:
ALT - Pin 6:
ADR - Pin 7:
DQ - Pin 8:
GND
Verification passed: the new header nets are connected and ERC checks showed no open schematic issues. I also updated Concise BOM - Part Name, Value, Designators and Circuit and Documentation Reverification.
Fix issues and verify
Add ALRT pull-up
Make pull-ups populated
Update all documentation
Run full review
Explain header wiring
Refine this doc
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ESP32 and Arduino Uno Datasheet Summary
Scope and Assumptions
This is a practical, datasheet-style engineering summary for comparing and using:
- ESP32 target: ESP32-WROOM-32 / ESP32 DevKit style boards, based on Espressif ESP32 series modules.
- Arduino target: Arduino Uno Rev3, based on ATmega328P at 16 MHz.
Exact ESP32 pin availability depends on the specific development board. Always check the pinout of the exact ESP32 board you buy.
Quick Comparison
Table
| Feature | Arduino Uno Rev3 | ESP32-WROOM-32 / DevKit |
|---|---|---|
| Main MCU | ATmega328P | ESP32 dual-core Xtensa LX6 |
| Logic voltage | 5 V | 3.3 V only |
| Typical board supply | USB 5 V or barrel/VIN | USB 5 V to onboard 3.3 V regulator |
| Recommended external input | 7-12 V via VIN/barrel on Uno | Board-dependent; usually 5 V pin/VIN or USB |
| Clock | 16 MHz | Up to 240 MHz |
| Digital GPIO | 14 Uno digital pins | Board-dependent, many GPIOs |
| PWM | 6 Uno PWM pins | LEDC PWM on many GPIOs |
| ADC | 10-bit ADC, 6 analog inputs on Uno | 12-bit SAR ADC, many channels but non-linear without calibration |
| DAC | None | 2 DAC outputs on GPIO25/GPIO26 on classic ESP32 |
| I2C | A4 SDA, A5 SCL | Flexible GPIO assignment, common SDA=21, SCL=22 |
| SPI | D10-D13 / ICSP | Flexible; common VSPI pins GPIO23/19/18/5 |
| UART | 1 hardware UART exposed on D0/D1 | Multiple UARTs |
| Wireless | None | 2.4 GHz Wi-Fi + Bluetooth/BLE |
| USB native | USB-serial bridge only | Usually USB-serial bridge; not native USB on classic ESP32 |
Arduino Uno Rev3 Key Datasheet-Style Specs
Core
- Microcontroller: ATmega328P.
- Architecture: 8-bit AVR.
- Clock: 16 MHz on Arduino Uno Rev3.
- Flash memory: 32 KB, with bootloader space used on Arduino boards.
- SRAM: 2 KB.
- EEPROM: 1 KB.
Power
- Operating logic voltage: 5 V.
- Recommended input voltage through barrel/VIN: 7-12 V.
- Input voltage limit commonly specified for Uno-class boards: 6-20 V, but using high input voltage increases regulator heating.
- 3.3 V output exists on the board but is for small external loads only.
- Supplying regulated power directly into 5V or 3.3V pins bypasses onboard protection/regulation and should be done carefully.
Digital I/O
- 14 digital I/O pins: D0-D13.
- 6 PWM-capable pins: D3, D5, D6, D9, D10, D11.
- Logic high is 5 V.
- Common design recommendation: keep GPIO current modest; Arduino documentation commonly recommends 20 mA per I/O pin as a practical limit.
Analog Input
- 6 analog inputs: A0-A5.
- ADC resolution: 10-bit.
- ADC code range: 0-1023.
- Default ADC reference: AVCC, normally 5 V.
- Approximate ADC step at 5 V reference: 4.88 mV/count.
- For pH measurement, the Uno ADC alone is much less sensitive than ADS1115.
Communication Interfaces
- UART: D0 RX, D1 TX.
- I2C: A4 SDA, A5 SCL.
- SPI: D10 SS, D11 MOSI, D12 MISO, D13 SCK; also on ICSP header.
pH Sensor Interface Notes for This Project
- Uno is compatible with the current 5 V design.
- Connect VCC_5V to Uno 5V, GND to Uno GND, SDA to A4, SCL to A5.
- DS18B20_DATA can connect to a digital pin such as D2 or D3.
- The ADS1115 provides much finer pH voltage resolution than the Uno ADC.
ESP32-WROOM-32 / ESP32 DevKit Key Datasheet-Style Specs
Core
- MCU: ESP32 dual-core 32-bit Xtensa LX6.
- Clock: commonly up to 240 MHz.
- Wireless: 2.4 GHz Wi-Fi plus Bluetooth/BLE.
- Module clock: common ESP32-WROOM-32 modules use a 40 MHz crystal.
- Flash: module-dependent; common ESP32-WROOM-32 modules often include 4 MB SPI flash.
Power
- ESP32 chip/module operating voltage: 3.0 V to 3.6 V, nominal 3.3 V.
- ESP32 GPIO are not 5 V tolerant.
- DevKit boards usually accept 5 V on USB/VIN and regulate it to 3.3 V.
- Power supply must handle Wi-Fi current peaks; use a regulator capable of at least several hundred mA. Many references recommend designing for around 500 mA available to the module/board.
Digital I/O and Boot-Strap Warnings
ESP32 has many GPIOs, but not all are safe as general-purpose external I/O.
Important caution pins:
- GPIO0: boot mode strap; affects flashing/boot.
- GPIO2, GPIO4, GPIO5, GPIO12, GPIO15: strap or boot-sensitive pins depending on module/board.
- GPIO6-GPIO11: commonly connected to SPI flash; do not use on WROOM modules.
- GPIO34-GPIO39: input-only on classic ESP32.
For beginner-friendly external sensors, prefer board-recommended GPIOs such as GPIO21/22 for I2C and GPIO25/26/27/32/33 for general I/O/ADC where available.
Analog Input
- ESP32 includes SAR ADC channels, commonly referred to as ADC1 and ADC2.
- ADC nominal resolution is up to 12-bit.
- ADC accuracy is not as linear as a precision external ADC; calibration is recommended.
- ADC2 has restrictions when Wi-Fi is active on classic ESP32, so prefer ADC1 pins for analog sensing.
Communication Interfaces
- I2C: flexible pin assignment. Common defaults are SDA=GPIO21 and SCL=GPIO22.
- SPI: flexible pin assignment. Common VSPI defaults are MOSI=GPIO23, MISO=GPIO19, SCK=GPIO18, CS=GPIO5.
- UART: multiple UARTs available; default programming UART usually uses GPIO1 TX0 and GPIO3 RX0.
- PWM: LEDC peripheral can generate PWM on many output-capable GPIOs.
pH Sensor Interface Notes for This Project
If using ESP32 instead of Arduino Uno:
- Power the ADS1115 module, DS18B20 pull-up, I2C pull-ups, and VBIAS divider from 3.3 V, not 5 V.
- Do not feed 5 V I2C or 5 V DS18B20 data into ESP32 GPIO.
- pH accuracy is not inherently worse at 3.3 V if the ADS1115 PGA range is configured correctly.
- Recommended ADS1115 pH setting remains differential AIN0-AIN1 with a suitable PGA such as +/-1.024 V.
- Bias midpoint becomes approximately 1.65 V instead of 2.5 V.
Compatibility With Current ADS1115 pH Project
ADS1115 Wiring Notes
ADS1115 Pin Functions Used in This pH Project
Table
| ADS1115 Module Pin | Project Net | Function |
|---|---|---|
| VCC | VCC_5V or 3V3 | ADC module supply. Use 5 V for Arduino Uno, 3.3 V for ESP32. |
| GND | GND | Common ground with the microcontroller and sensor board. |
| SDA | I2C_SDA | I2C data line. Needs pull-up to the microcontroller logic voltage. |
| SCL | I2C_SCL | I2C clock line. Needs pull-up to the microcontroller logic voltage. |
| ADDR | ADS_ADDR | Address select. Tie to GND, VCC, SDA, or SCL to choose the I2C address. |
| ALRT/RDY | ADS_ALERT | Optional alert/ready output. Can be left unused or connected to an interrupt-capable GPIO. |
| A0 | ADC_PH_PLUS | Buffered pH probe signal. |
| A1 | ADC_PH_MINUS | Buffered VBIAS reference. pH is measured differentially as A0 - A1. |
| A2 | ADS_AIN2 | Spare auxiliary analog input. |
| A3 | ADS_AIN3 | Spare auxiliary analog input. |
Arduino Uno Wiring
Use this wiring when using Arduino Uno, Nano, or Mega style 5 V Arduino boards:
Table
| Project Signal | Arduino Uno Pin | Notes |
|---|---|---|
| VCC_5V | 5V | Powers ADS1115 module, op amp, bias network, and pull-ups. |
| GND | GND | Common ground. |
| I2C_SDA | A4 / SDA | Arduino Uno I2C data. |
| I2C_SCL | A5 / SCL | Arduino Uno I2C clock. |
| ADS_ALERT | Optional D2 or D3 | Only needed if using ALERT/RDY interrupt mode. Otherwise leave unconnected. |
| ADS_ADDR | GND recommended | Gives the default ADS1115 address 0x48 on most ADS1115 libraries. |
| DS18B20_DATA | D2 or D3 | Uses R11 = 4.7 kohm pull-up to 5 V in the current design. |
| AUX_SENSOR_AIN2_IN | External analog sensor output | Must stay between 0 V and 5 V. |
| AUX_SENSOR_AIN3_IN | External analog sensor output | Must stay between 0 V and 5 V. |
Recommended Arduino Uno ADS1115 firmware settings:
- Use I2C address 0x48 if ADS_ADDR is tied to GND.
- Read pH in differential mode: A0 - A1.
- Start with PGA = +/-1.024 V for pH because the pH signal is small.
- Use a slow data rate such as 8 SPS or 16 SPS and average readings.
- Do not read the pH probe with the Arduino Uno analog input; use the ADS1115 result.
ESP32 Wiring
Use this wiring when using ESP32-WROOM-32 / ESP32 DevKit style 3.3 V boards:
Table
| Project Signal | ESP32 DevKit Pin | Notes |
|---|---|---|
| 3V3 rail | 3V3 | The design must be converted from VCC_5V to 3.3 V for ESP32 use. |
| GND | GND | Common ground. |
| I2C_SDA | GPIO21 typical | I2C data. Pull up to 3.3 V only. |
| I2C_SCL | GPIO22 typical | I2C clock. Pull up to 3.3 V only. |
| ADS_ALERT | Optional GPIO25, GPIO26, GPIO27, GPIO32, or GPIO33 | Use only if ALERT/RDY interrupt is required. Avoid boot-strap pins. |
| ADS_ADDR | GND recommended | Gives default ADS1115 address 0x48. Tie to 3.3 V/SDA/SCL only if another address is needed. |
| DS18B20_DATA | GPIO25, GPIO26, GPIO27, GPIO32, or GPIO33 typical | Pull up to 3.3 V only. Avoid 5 V pull-up. |
| AUX_SENSOR_AIN2_IN | 0-3.3 V sensor output | Must never exceed 3.3 V unless level shifted/divided. |
| AUX_SENSOR_AIN3_IN | 0-3.3 V sensor output | Must never exceed 3.3 V unless level shifted/divided. |
ESP32 safety requirements:
- ESP32 GPIO are not 5 V tolerant.
- Do not connect the current 5 V I2C pull-ups directly to ESP32.
- Do not connect DS18B20_DATA with a 5 V pull-up to ESP32.
- If reusing this exact board with an ESP32, either revise the board to 3.3 V or add proper level shifting on I2C and DS18B20 data.
- Avoid ESP32 GPIO6-GPIO11, which are usually connected to internal flash.
- Avoid GPIO0 and other boot-strap pins for external sensor wiring unless you understand the boot requirements.
Recommended ESP32 ADS1115 firmware settings:
- Use Wire.begin(21, 22) for common ESP32 SDA/SCL wiring, unless your board uses different pins.
- Use I2C address 0x48 if ADS_ADDR is tied to GND.
- Read pH in differential mode: A0 - A1.
- PGA = +/-1.024 V is still suitable for pH at 3.3 V.
- The pH bias midpoint should be approximately 1.65 V in a 3.3 V version.
- Prefer ADS1115 over ESP32 internal ADC for pH because ESP32 ADC is not precision-linear without calibration.
Best for Arduino Uno/Nano/Mega
Use the current 5 V configuration:
- VCC_5V -> Arduino 5V.
- GND -> Arduino GND.
- SDA/SCL -> Arduino I2C pins.
- DS18B20_DATA -> any Arduino digital GPIO with R11 = 4.7 kohm pull-up to 5 V.
- ADS1115 reads pH differentially on A0-A1.
Best for ESP32 / 3.3 V Arduino
Revise the project rails to 3.3 V:
- Rename or treat VCC_5V as 3V3.
- Pull I2C SDA/SCL to 3.3 V.
- Pull DS18B20_DATA to 3.3 V.
- Use VBIAS = 1.65 V from equal divider resistors.
- Confirm the ADS1115 module supports 3.3 V operation.
- Ensure any auxiliary AIN2/AIN3 sensors output 0-3.3 V only.
Practical Design Recommendation
For a beginner Arduino pH project, Arduino Uno + ADS1115 is simpler and safer because it matches the current 5 V through-hole design. If you want Wi-Fi/Bluetooth logging, ESP32 is better, but the board should be revised to a 3.3 V-safe version so no ESP32 GPIO ever sees 5 V.
Source Notes
Primary references used for this summary:
- Espressif ESP32-WROOM-32 and ESP32 series datasheet information.
- Arduino Uno Rev3 technical specifications / datasheet.
- Microchip ATmega328P datasheet information.
Scope and Assumptions
Quick Comparison
Arduino Uno Rev3 Key Datasheet-Style Specs
Core
Power
Digital I/O
Analog Input
Communication Interfaces
pH Sensor Interface Notes for This Project
ESP32-WROOM-32 / ESP32 DevKit Key Datasheet-Style Specs
Core
Power
Digital I/O and Boot-Strap Warnings
Analog Input
Communication Interfaces
pH Sensor Interface Notes for This Project
Compatibility With Current ADS1115 pH Project
ADS1115 Wiring Notes
ADS1115 Pin Functions Used in This pH Project
Arduino Uno Wiring
ESP32 Wiring
Best for Arduino Uno/Nano/Mega
Best for ESP32 / 3.3 V Arduino
Practical Design Recommendation
Source Notes
