OpenOrti hardware

High-frequency-reflectometry soil moisture sensor. A differential ring oscillator drives a transmission line in the soil; soil permittivity shifts the oscillation frequency, which a reciprocal counter measures. Connectivity to the outer world and count storage is handled by an onboard MCU.

Root sheet: openorti.kicad_sch. It wires the blocks below and exposes the board signals on two 10-pin headers (J1, J2).

Folders

Folder	Contents
`power/`	18650 cell, charger, USB-C, 3.3 V booster
`oscillator/`	Ring oscillator, LVDS conditioning, /2 and /4 dividers
`analog/`	Differential pair and current mirror primitives
`measurement/`	Reciprocal frequency counter
`tests/`	Simulation testbenches, aggregated by `tests/tests.kicad_sch`
`experiments/`	Unwired or unfinished sheets
`models/`	Vendor SPICE models, symbols, footprints

Signal chain

power -> 3.3V -> oscillator/differential_ring_oscillator
                     -> oscillator/oscillator_output_conditioning -> clock
                     -> measurement/reciprocal_frequency_measurement

analog/ holds the primitives the oscillator is built from.

Project variables

Values referenced across the schematics, from openorti.kicad_pro:

Variable	Value
`R_diff_amp`	`100`
`R_mirror`	`400`
`R_mirror_diff_amp`	`150`
`R_mirror_offset`	`50`
`R_mix_mirror`	`200`
`R_mix_pair`	`100`
`R_offset`	`800`
`R_pair`	`160`
`R_sum_A`	`1000`
`R_sum_B`	`100`
`Vcc`	`3.3`