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Battery Tracking

CD Thread: https://www.chiefdelphi.com/t/rfid-battery-tracking-some-progress/502847

Video demo: https://www.youtube.com/watch?v=rKZOKIWVOAg

Developed with wpilib 2025 and the latest firmware avaliable at the time for REV PDH and CTRE PDP.

For 2026 build season our team will be focusing on Addressable LED + RFID combo firmware. This one might be slightly out dated.

Combo Firmware: https://github.com/sikaxn/FRC-Custom-CAN-Sensor/tree/dev-board/Arduino/BatteryLEDCombo

Getting Started

https://github.com/sikaxn/FRC-Custom-CAN-Sensor/wiki/900.-IronMaple-RFID-Battery-Tracking-Solution

Android Companion APP and roboRIO Driver

(new for preview firmware) https://github.com/sikaxn/FRC-Custom-CAN-Sensor/tree/dev-board/roboRIO/batteryReaderNew

https://github.com/sikaxn/FRC-RFID-Battery-Reader/

roboRIO Driver is only needed if you want to read battery data, or if your Power Distro device can not be connected to CAN (PDP 2.0). Auto energy usage monitoring is only supported with PDP 1.0 or PDH as roboRIO can not provide total current data. Alternatively, you could use roboRIO driver to update energy calculated by yourself.

https://github.com/sikaxn/FRC-Custom-CAN-Sensor/tree/main/roboRIO/batteryReader

To be done

  1. DONE Reading date and time from roboRIO Heartbeat
  2. DONE Auto discovery of CTRE PDP or REV PDH so no more requirement of having roboRIO Driver sending voltage and energy (unless using PDP 2.0)

Arduino IDE Setup

This Library needs to be manually installed to handle NDEF encoding.

https://github.com/Seeed-Studio/Seeed_Arduino_NFC

these can be installed using arduino library manager

https://github.com/OSSLibraries/Arduino_MFRC522v2 https://github.com/bblanchon/ArduinoJson

Example RFID Reader holder

https://makerworld.com/en/models/1504037-frc-battery-tracking-example-rfid-reader-holder#profileId-1573770

Logic

  1. When ESP32 power up, it will scan on both reader (I have 2 reader attached assuming a battery can be installed in any direction), once a card is found, it will lock on with that reader.
  2. once a reader is chosen, it will pull data from battery and send it to CAN. A new usage record is created with voltage, date, etc all 0 because at this time roboRIO isn’t fully booted yet.
  3. once a meaningful date message (roboRIO get its date time after attaching to DS) is received from roboRIO, it will update the date on that record
  4. robot start being driven, tested, etc. ESP32 monitor voltage sent from roboRIO and record the lowest value
  5. robot is disabled. disable will trigger a write. Latest date time, voltage energy is written to battery
  6. robot is re enabled… and disabled. every time robot is disabled, that record is updated.
  7. we are done with robot, battery removed from robot, and data could be pulled by android APP.

Card and data format

Data is stored on Mifare Classic 1K card are NDEF formatted json. Docs

Wiring (legacy)

Please refer to wiki Getting Started for the latest wiring.

image

Peripheral Function ESP32 Pin Notes
RC522 Reader 1 SPI SS (Slave Select) GPIO 5 Connected to ss_pin1
RC522 Reader 2 SPI SS (Slave Select) GPIO 4 Connected to ss_pin2
RC522 Shared RST (Reset) GPIO 22 Used for both readers
SPI (Shared) SCK (Clock) GPIO 18 Used for both readers
MISO (Master In Slave Out) GPIO 19 Used for both readers
MOSI (Master Out Slave In) GPIO 23 Used for both readers
CAN TX Transmit Line GPIO 16 Connected to CAN transceiver TX
CAN RX Receive Line GPIO 17 Connected to CAN transceiver RX

CAN Message Types in Use

Please refer to comments in roboRIO driver for the latest CAN protocol.

https://github.com/sikaxn/FRC-Custom-CAN-Sensor/blob/dev-board/roboRIO/batteryReaderNew/src/main/java/frc/robot/subsystems/batteryCAN.java

Note these is only ESP32 <-> RIO protocol. For PDP / PDH -> ESP32 protocol, refer to wpilib code. ESP32 will not send frame to PDP / PDH. It only listen for it.

CTRE PDP: https://github.com/wpilibsuite/allwpilib/blob/main/hal/src/main/native/athena/CTREPDP.cpp REV PDH: https://github.com/wpilibsuite/allwpilib/blob/main/hal/src/main/native/athena/rev/PDHFrames.h

CAN Message Types in Use (legacy)

1. Heartbeat (robot status) — CAN ID = 0x01011840 rio -> ESP32

  • Fixed ID sent by roboRIO

  • 8-byte payload, where:

    • data[4] & (1 << 4) = robot enabled status (bit 4)

2. BATTERY_STATUS_API_ID_1 (apiID = 0x135) rio -> ESP32

  • ID = calculated by makeCANMsgID(...)

  • 7+ bytes payload:

    Byte 0: year (offset from 2000, e.g., 25 for 2025)
Byte 1: month
Byte 2: day
Byte 3: hour
Byte 4: minute
Byte 5: second
Byte 6: voltage * 10 (e.g., 139 = 13.9V)

3. BATTERY_STATUS_API_ID_2 (apiID = 0x136) rio -> ESP32

  • 2 bytes payload:

    Byte 0–1: Energy (uint16_t)

4. RFID Meta Info

  • API IDs: 0x131, 0x132, 0x133
  • Used to send metadata after tag read
➤ 0x131: Battery Serial (first 8 bytes) ESP32 -> rio
Byte 0–7: ASCII characters of SN
➤ 0x132: Datetime + Voltage Info ESP32 -> rio
Byte 0: Year (offset from 2000, e.g., 25 = 2025)
Byte 1: Month (1–12)
Byte 2: Day of Month (1–31)
Byte 3: Hour (0–23)
Byte 4: Minute (0–59)
Byte 5: Second (0–59)
Byte 6: Voltage × 10 (e.g., 13.9V → 139)
Byte 7: Reserved (set to 0)
➤ 0x133: Cycle count + note ESP32 -> rio
Byte 0–1: Cycle count (uint16_t)
Byte 2: Note type (0 = normal, 1 = practice, 3 = Scrap, 4 = Other)