The pH FeatherWing V0.2 is a pH electrode amplifier which is designed to be compatible with the Feather/FeatherWing system. It fits in a standard FeatherWing doubler or tripler base and is compatible with any Feather Development board which adheres to Adafruit's Feather specification.
The pH FeatherWing is sold as a kit including the FeatherWing v0.2 board plus through-hole components (1 x BNC, 1 x screw terminal connector and 2 x headers). Instructions for assembly can be found here: Assembly of the pH FeatherWing.
The pH electrode amplifier on this FeatherWing is based on the Microchip MCP6002 dual operational amplifier which has a low input bias current of 1pA. A standard BNC connector is used to connect to the pH electrode making the pH FeatherWing compatible with most common pH probes. In addition to the pH electrode amplifier the pH FeatherWing includes a 3-position screw terminal connector for attaching a water proof DS18B20 temperature sensor. This enables simultaneous pH and temperature measurements and gives the user the the capability to compensate the pH readings for changes in temperature.
The pH Feather wing has two buttons labeled "pH7" and "pH4/10" which are connected to digital pins D12 and D13 on the Feather development board. These buttons can be used to initiate calibration procedures in the Feather firmware (see blog post Creating a pH meter using the pH FeatherWing).
Additional information can be found at the links below:
- pH FeatherWing V0.2 schematic
- KiCad Design files
- pH Meter firmware example (CircuitPython)
Note, the previous version of this design, pH FeatherWing V0.1, was based on is based on Texas Instruments ultra low input bias current (3 fA) LMP7721 precision operational amplifier. The two designs are functionally the same. The schematic for the V0.1 design can be found here.
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