2024

Multiplexed Resistivity Measurement System

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This article describes work around a multiplexed resistivity measurement device, focused on multi-channel acquisition, removable contacts, and USB interfacing.

The design is based on an STM32F030 microcontroller, used to sequence measurements across multiple electrode points, handle basic signal processing, and communicate with a host over USB.

Channel selection is done through I/O expanders and multiplexing, allowing many electrodes to be scanned without manual rewiring. Connections are made using pogo pins to provide repeatable contact while keeping the setup removable and fast to install.

The device uses USB-C for both power and data transfer, supporting a compact and portable form factor.

Overall, the work centers on combining multiplexed routing, reliable contact mechanics, and embedded control to automate multi-point resistivity measurements.

Power Converter with RS485 Telemetry

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This article describes an embedded controller for a few-hundred-watt DC power conversion stage, focused on real-time measurement, MPPT control logic, and protection handling.

The design is based on an STM32F334 (timers/ADC well-suited for power control). The firmware acquires bus voltage and current via synchronized ADC sampling, applies basic filtering, and computes instantaneous power for regulation and monitoring.

A closed-loop control implements MPPT by adjusting the converter operating point through PWM duty cycle updates. The power stage includes a boost converter sized for ~48 V class operation, with control features such as soft-start, duty limiting, and fault-driven shutdown.

For protection, an independent path can engage a dump load to clamp bus overvoltage and absorb excess energy when required. Fault handling covers typical events such as overvoltage/overcurrent and temperature-dependent derating (depending on available sensing).

Telemetry and external control are provided through RS485 (Modbus), exposing measurements, state, and fault codes for supervision.

Wi-Fi Router with AC and Battery Power

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This article describes work around a compact networking device built on an ESP32 (ESP32-D0WDQ6-V3), focused on Wi-Fi connectivity, packet routing, and power management.

The firmware configures the ESP32 to operate with multiple Wi-Fi roles (e.g., uplink + local access), handling link monitoring, reconnection logic, and basic system supervision (watchdog, status reporting).

Power design supports mains operation (230 VAC) through an AC-DC stage, with an integrated Li-Ion backup battery for continuity during interruptions. A battery management section handles safe charging, protection, and voltage monitoring to prevent undervoltage operation and ensure predictable behavior when switching between power sources.

Overall, the work combines Wi-Fi routing, reliability-focused firmware, and dual-source power management in a small standalone platform.