Author: dwc5496

• Project Overview:
  • This PCB design implements a compact XT60 inline current meter module powered by an ESP-01 microcontroller and the INA219 bi-directional current/power monitor. The board measures voltage and current from 5–26V DC, with a configurable sensing range up to 40A for high-power applications such as LED strips and RC batteries or even 3D Printers.
  • It features full Home Assistant integration via ESPHome, delivering real-time telemetry of voltage, current, shunt voltage, and power, with OTA firmware update capability.

Design Details:

• XT60 In-Line PCB:
  • The board is designed in a panelized layout for multi-channel assembly (up to 4 meters per PCB). Both the input and output are XT60 connectors, providing low-resistance, high-current connections.
  • Wide copper pours and short traces minimize voltage drop and thermal loss even at high currents.

• Current & Voltage Sensing:
  • INA219 monitors both bus voltage and shunt current using precision 20mΩ resistors (configurable for other shunt values). Up to four parallel channels are supported per board for multi-circuit monitoring.
  • Jumper settings allow for easy configuration of sensing channels and measurement range.

• Onboard Power Regulation:
  • An integrated buck converter (U8) steps down input voltage (5–26V) to 3.3V for the ESP-01 and sensor ICs, ensuring stable operation across wide input ranges.

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• MCU & Connectivity:
  • The ESP-01S WiFi microcontroller hosts the ESPHome firmware and handles I2C communication with the INA219 sensors.
  • All sensor values are published to Home Assistant, and the device supports OTA firmware upgrades for easy maintenance and updates.

Module Assembly:

• The module fits directly between any DC power source and load. The final product shown here features XT60 connectors and heat-shrink insulation for safe, robust inline installation.

ESPHome & Home Assistant Integration:

• With default ESPHome YAML, the sensor publishes bus voltage, current, power, and shunt voltage readings. All values are accessible for automations and graphical dashboards in Home Assistant.

Recently I replaced the instrument cluster (combination meter) in my 2005 Nissan Altima. After installing the new one, I noticed two things. First, the mileage is incorrect—which was expected—the old cluster had 190k miles and the new one shows just over 260k. That’s not a huge deal; I’ll just write down the difference and keep it in the glove box. But I also noticed the old meter was a “With NAVI” unit, while the new one is “Without NAVI.” What does NAVI mean? I have no idea, BUT I prefer the new cluster since it displays more information on the dashboard.

The Odometer

There are services that will reprogram your odometer, typically for around $250. When buying a used instrument cluster, many places offer to match the odometer reading if you send yours in. So, it’s possible to alter the reading. However, aside from the $3,000 Nissan Consult II programmer, I haven’t found a scan tool that supports this function.

Now for the Hacking

EEPROM swapping and reprogramming are very common among car modders. However, I couldn’t find any info specific to the Altima combination meter, so let’s crack it open and see what we find.

The two SOIC chips near the main MCU are the AB2C250 CAN transceiver and the 93C66 serial EEPROM. Taking a closer look at the EEPROM, we can verify the pinout—pins 6, 7, and 8 are all shorted and tied to VCC; pin 5 is tied to ground with a bypass capacitor between them.

After wiring into the EEPROM and connecting it to my Saleae Logic 4 analyzer, we can see that at power-up there are seven distinct transactions with the EEPROM.

Verify Our Assumptions

Currently, we’re assuming the mileage is stored in this EEPROM chi, but we don’t have any real evidence yet, other than “it makes sense.” So… What can we do? Remove the chip and see what happens, right?
Well, not exactly. Instead of removing the chip, you can break the communication circuit. The CS pin is connected to the main MCU via a 470 ohm resistor, so you can safely short the EEPROM side of that resistor to ground. This prevents the MCU from “talking” to the EEPROM.

SUCCESS! (Kinda?)

Now, the odometer reads 0 miles, but the display shows DTE, and I can scroll through MPG and MPH. So… looks like this is a “Without NAVI” dashboard now?

Summary

We found the EEPROM chip on the combination meter board, captured the communication between the EEPROM and the MCU, and confirmed that both the odometer value and the “With/Without NAVI” configuration are stored in the EEPROM.

Next, we’ll need to analyze the communication export and try to reconstruct the memory map of the EEPROM chip itself. Then, we’ll need to decode the bitmap for odometer and configuration data.