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LeoPhi A USB Enabled pH Sensor Interphase on an Arduino Leonardo

Want pH sensing on your project? Check this pH sensor interphase from sparky's widget. It can work with a computer through USB and by itself (stand alone).


It's built on an Atmega32u4 with a modified Arduino Leonardo (thus the leo in the name?) bootloader. Environmental parameters are gathered through a pH sensor, an LM335A temperature sensor and an analog humidity sensor. The analog signal from the pH sensor goes through an offset introducing fixed gain op-amp circuit that centers the signal into the range of the Atmega32u4's Analog to Digital Converter (ADC) Pins. The parameters are then printed out into a four liner Liquid crystal display (LCD).

This project also has calibration routine and when used with a computer you can send commands to set the LeoPhi into specific modes. Click on the read more below to see the command list.



  • C – Continous Read Mode: Dump readings and data every second

  • R – Single pH reading: response “pH: XX.XX” where XX.XX is the pH

  • E – Exit continuous read mode

  • S – set pH7 Calibration point

  • F – set pH4 Calibration point: also recalcs probe slope and saves settings to EEPROM

  • T – set pH10 Calibration point: also recalcs probe slope and saves settings to EEPROM

  • X – restore settings to default and ideal probe conditions

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