Isolated Multi Rail Power Supply Monitor Sensor Board

Multi-Rail Isolated Power Supply Monitoring System

Repository: PS_Monitor
Author: Mike Capotosto

Project Overview

The Multi-Rail Isolated Power Supply Monitoring System measures the voltage and current of up to six floating power-supply rails while preserving galvanic isolation between measurement channels. Each rail is monitored by an LTC2945 power monitor connected through an isolated I²C interface to an Arduino GIGA R1 WiFi. The Arduino firmware performs data acquisition, engineering-unit conversion, alarm evaluation, persistent configuration storage, local display control, HTTP service, and Ethernet communication with an EPICS Input/Output Controller. Measurement and status information is presented locally on the GIGA Display Shield, through a browser-based dashboard, and remotely through a Phoebus Control System Studio operator interface.

The monitored rails are:

• +5VA
• +5VB
• +5V
• -5V
• +15V
• -15V

System Features

• Six isolated voltage and current measurement channels
• LTC2945 voltage, current, and power monitoring
• Independent I²C isolation for each floating rail
• Support for positive and negative supply rails
• Configurable upper and lower voltage limits
• Configurable upper and lower current limits
• Persistent alarm and network settings stored in internal QSPI flash
• Local touchscreen display using the Arduino GIGA Display Shield
• Browser-based monitoring and configuration dashboard
• Ethernet communication through the Arduino Ethernet Shield
• PSC (Portable Streaming Controller) protocol interface for EPICS integration
• EPICS Process Variables for measurements, limits, alarms, and status
• Phoebus OPI for centralized operator monitoring
• I²C communication-error detection
• Text-based alarm states such as OVL, UVL (over/under voltage limit), OCL, and UCL (over/under current limit)

System Architecture

Data Flow

┌──────────────────────────────────────────────┐
│ Floating Power-Supply Rails                  │
│ +5VA, +5VB, +5V, -5V, +15V, and -15V        │
└──────────────────────┬───────────────────────┘
                       │
                       ▼
┌──────────────────────────────────────────────┐
│ LTC2945 Voltage and Current Monitors         │
│ One monitor per power-supply rail            │
└──────────────────────┬───────────────────────┘
                       │
                       ▼
┌──────────────────────────────────────────────┐
│ Isolated I²C Interfaces                      │
│ Maintains isolation between floating rails   │
└──────────────────────┬───────────────────────┘
                       │
                       ▼
┌──────────────────────────────────────────────┐
│ Arduino GIGA R1 WiFi Firmware                │
│                                              │
│ • Sensor acquisition                         │
│ • Engineering-unit conversion                │
│ • Negative-rail sign correction              │

Major Subsystems

Repository Structure

PS_Monitor/
├── README.md
├── hardware/
│   ├── kicad/
│   ├── bom/
│   ├── gerbers/
│   ├── mechanical/
│   └── datasheets/
├── firmware/
│   ├── platformio.ini
│   ├── include/
│   ├── lib/
│   ├── src/
│   └── test/
├── epics-ioc/
│   ├── configure/
│   ├── db/
│   ├── dbd/
│   ├── iocBoot/
│   ├── psuMonitorApp/
│   └── opi/
└── documentation/

Directory Descriptions

• /hardware
  KiCad schematic and PCB files, manufacturing outputs, bill of materials, mechanical drawings, and related.

• /firmware
  PlatformIO project for the Arduino GIGA R1 WiFi. This directory contains the application source code, configuration headers, local libraries, and build configuration.

• /epics-ioc
  EPICS IOC source tree containing database files, record definitions, startup scripts, PSCDriver configuration, device communication settings, and Phoebus Control System Studio displays.

• /documentation
  Assorted Documentation

Hardware

Primary Components

• Arduino GIGA R1 WiFi
• Arduino GIGA Display Shield
• Arduino Ethernet Shield
• LTC2945 voltage, current, and power monitors
• DC1697A LTC2945 demonstration board for prototype testing
• Per-channel I²C digital isolators
• Current-sense shunt resistors
• Custom monitoring and interface PCB
• Six isolated power-supply inputs

Measurement Method

Each LTC2945 measures:

• Supply voltage
• Differential voltage across a current-sense shunt
• Calculated load current
• Calculated electrical power

Because each monitored supply may float at a different potential, every sensor channel communicates through its own isolated I²C interface. Negative rails are monitored within their isolated domains, and the firmware applies the appropriate sign to the reported engineering values.

Firmware

The firmware is built with PlatformIO using the Arduino Mbed OS framework.

Main Firmware Modules

Firmware Configuration

Hardware-specific settings are stored in configuration headers, including:

• I²C addresses
• Shunt-resistance values
• Channel names
• Rail polarity
• Voltage and current scaling
• Default alarm limits
• Static network configuration
• MAC address
• PSC port configuration
• Sensor polling intervals

Persistent Settings

The firmware stores configuration data in the Arduino GIGA internal QSPI flash using LittleFS.

Saved settings include:

• Per-channel voltage-low limit
• Per-channel voltage-high limit
• Per-channel current-low limit
• Per-channel current-high limit
• Static IP address
• Subnet mask
• Gateway address
• DNS server address

Network Interfaces

HTTP Dashboard

The firmware hosts a local web interface for:

• Viewing voltage and current measurements
• Viewing alarm and communication status
• Editing alarm limits
• Editing network parameters
• Saving settings to QSPI

PSC Protocol

The Arduino exposes a PSC protocol service over Ethernet. The EPICS IOC connects to the device using PSCDriver and maps transmitted parameters into EPICS records.

EPICS IOC

Requirements

• EPICS Base
• ASYN
• PSCDriver
• A supported Linux environment
• Phoebus for the operator interface

Build the IOC

From the repository root:

cd epics-ioc
make

Start the IOC

cd iocBoot/iocpsuMonitor
./st.cmd

An equivalent direct launch command may also be used:

../../bin/linux-x86_64/psuMonitor st.cmd

Example IOC Configuration

P=TEST:
R=GIGA
DEVICE=GIGA_PSC
HOST=192.168.1.177
PORT=8765

The final values are defined in the IOC startup script.

EPICS Process Variables

The IOC is intended to provide Process Variables for:

• Channel voltage
• Channel current
• Voltage-low limit
• Voltage-high limit
• Current-low limit
• Current-high limit
• Voltage alarm status
• Current alarm status
• Sensor communication status
• I²C error status
• Arduino connection status
• Network information
• Firmware status

Alarm States

Operator Interface

The Phoebus OPI provides a centralized display for all monitored rails.

Planned or implemented interface elements include:

• Voltage and current readbacks
• Alarm-limit displays
• Text-based alarm indicators
• Connection-status indicator
• I²C error indicator
• Per-channel status cards
• Network and firmware information
• Overall system status

Project Milestones

• Define system requirements and monitored power rails
• Select the Arduino GIGA R1 WiFi as the primary controller
• Establish the PlatformIO firmware project
• Develop the initial six-channel display layout
• Add configurable voltage and current alarm limits
• Establish the Ethernet and PSC communication architecture
• Complete single-channel LTC2945 prototype validation
• Verify current scaling for each shunt-resistor value
• Complete six-channel isolated I²C hardware
• Finalize persistent storage and recovery testing
• Complete browser-based configuration testing
• Finalize EPICS database records
• Complete Phoebus OPI
• Fabricate and assemble the custom PCB
• Calibrate all measurement channels
• Perform end-to-end system validation
• Complete final project documentation