Pb Monitor v2

pbMonitor V2 — 48V Battery Back Monitor

A compact, open-source battery monitoring system for 48V battery banks. Built around the ESP32-C6 Mini, it reads four voltage taps, bidirectional current, and up to four temperature sensors — displaying live data on a 0.96" OLED and flagging faults through status LEDs and serial output.

Features

• Voltage monitoring — measures four independent taps (12V, 32V, 48V, 64V) via a 12-bit SPI ADC
• Bidirectional current — charge and discharge detection with configurable sensitivity
• Temperature — up to 4× DS18B20 sensors on a single OneWire bus, fully bit-banged (no external library)
• Live OLED display — two alternating pages: voltages/current and temperatures
• Fault detection — overvoltage, undervoltage, overcurrent, overtemperature with hysteresis to prevent flicker
• Status LEDs — green = healthy, red = any active fault
• Non-blocking firmware — temperature conversion runs asynchronously; no delay() in the main loop
• Hardware watchdog — 5-second timeout reboots the system if any sensor stalls the loop
• Serial debug output — live readings at 115200 baud, all in a single batched line per cycle
• Custom PCB — KiCad hardware design files included

Repository Structure

pbMonitorv2/
├── src/
│   └── pbMonitor/
│       └── pbMonitor.ino       Main firmware (Arduino sketch)
├── hardware/
│   ├── *.kicad_pro             KiCad project file
│   ├── *.kicad_sch             Schematic source
│   ├── *.kicad_pcb             PCB layout source
│   ├── schematic.pdf           Exported schematic (human-readable)
│   └── BOM.csv                 Bill of materials
└── README.md

Hardware

Full component values and footprints are in hardware/BOM.csv. Schematic PDF: hardware/schematic.pdf.

Signal Chain

Battery tap ──► Resistor divider ──► TLV9004 op-amp ──► TLA2518 ADC ──► ESP32-C6

The op-amp buffers the resistor divider output and keeps the ADC input within the 0–3.3V safe range regardless of load on the divider.

Pin Map

ADC Channel Map

Getting Started

Prerequisites

• Arduino IDE 2.x or arduino-cli
• ESP32 board package by Espressif

Add the ESP32 board package URL in Arduino IDE preferences:

https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json

Then install: Boards Manager → esp32 by Espressif Systems

Libraries

Install via Arduino Library Manager:

OneWire and DallasTemperature are not required. The DS18B20 driver is built into the sketch.

Building with arduino-cli

# Compile
arduino-cli compile --fqbn esp32:esp32:esp32c6 src/pbMonitor/pbMonitor.ino

# Upload (replace /dev/ttyUSB0 with your port)
arduino-cli upload --fqbn esp32:esp32:esp32c6 --port /dev/ttyUSB0 src/pbMonitor/pbMonitor.ino

Upload Steps (Arduino IDE)

1. Open src/pbMonitor/pbMonitor.ino
2. Select board: Tools → Board → ESP32C6 Dev Module
3. Set the calibration constants (see below)
4. Click Upload

Calibration

All calibration constants are grouped at the top of pbMonitor.ino. No other changes are needed.

Voltage Divider Ratios

#define RATIO_64V   19.4f
#define RATIO_48V   14.6f
#define RATIO_32V   9.7f
#define RATIO_12V   3.7f

Calculate the ratio from your actual resistor values:

RATIO = (R_top + R_bottom) / R_bottom

Example: 180 kΩ top + 10 kΩ bottom → RATIO = 19.0

Measure the actual battery tap voltage with a multimeter and the corresponding ADC voltage at the op-amp output to verify or fine-tune.

Current Sensor

#define CURRENT_SENSITIVITY  0.066f   // V/A — adjust for your sensor

Common values:

The sensor must output VREF/2 = 1.65V at 0A. Positive current = charging, negative = discharging.

Protection Thresholds

#define PACK_OVERVOLTAGE    58.0f   // V  (~14.5V/cell × 4)
#define PACK_UNDERVOLTAGE   42.0f   // V  (~10.5V/cell × 4)
#define PACK_CONNECTED_MIN  5.0f    // V  below this = pack disconnected, no UV fault
#define OVERCURRENT_A       50.0f   // A  peak discharge limit
#define OVERTEMP_C          55.0f   // °C battery thermal limit

Fault thresholds include a built-in hysteresis deadband (FAULT_HYSTERESIS_V = 0.5V, FAULT_HYSTERESIS_A = 1A) so fault flags do not oscillate when a measurement hovers near a trip point.

OLED Display

The display alternates between two pages every 2 seconds.

Page 1 — Voltages & Current

┌──────────────────────────────┐
│ pbMonitor v2        [ OK  ] │
├──────────────────────────────┤
│ 64V: 54.2V  48V: 48.1V     │
│ 32V: 32.1V  12V: 12.8V     │
├──────────────────────────────┤
│ I:  +12.50 A                │
│ ▲ CHARGING                  │
├──────────────────────────────┤
│ System Normal               │
└──────────────────────────────┘

Page 2 — Temperatures

┌──────────────────────────────┐
│ pbMonitor v2   Temps        │
├──────────────────────────────┤
│ T1:  32.5C   T2:  33.1C    │
│ T3:  31.8C   T4:  34.0C    │
├──────────────────────────────┤
│ Max:  34.0C                 │
└──────────────────────────────┘

Serial Monitor

Connect at 115200 baud. One line is printed per ADC cycle (500ms), followed by temperature lines when sensors are present:

64V:54.20 48V:48.10 32V:32.05 12V:12.80  I:+12.50A [CHARGING]
  T1: 32.5C
  T2: 33.1C

Active faults are appended inline:

64V:59.10 48V:52.30 32V:35.00 12V:13.10  I:+0.20A [IDLE]  !!OV

Fault Conditions

When any fault is active, the red LED turns on and the green LED turns off. The OLED status bar shows the active fault codes (e.g. OV OT). All faults clear automatically once the measured value recovers past the threshold plus the hysteresis deadband.

Firmware Architecture

The main loop is fully non-blocking and timer-driven:

The DS18B20 conversion window (750ms) runs concurrently with ADC reads and display updates — there is no delay() in the main loop.

Hardware Design Files

The hardware/ directory contains the complete KiCad project for the pbMonitor V2 PCB:

Designed in KiCad 7. Open the .kicad_pro file to load the full project.

License

MIT License — free to use, modify, and distribute with attribution. See LICENSE for full text.