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• Pin 1 (Pin_1): This pin is connected to the VBAT net, which typically supplies power to components.
• Pin 2 (Pin_2): This pin is connected to the ground (GND) net.

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• CFG_GPS0/SCK: Pin 16
• EXTINT0: Pin 4
• GND: Pins 10, 12, 13, and 24
• MISO/CFG_COM1: Pin 15
• MOSI/CFG_COM0: Pin 14
• RF_IN: Pin 11
• RSVD_17: Pin 17
• RSVD_8: Pin 8
• RXD1: Pin 21
• SCL2: Pin 19
• SDA2: Pin 18
• SS_N: Pin 2
• TIMEPULSE: Pin 3
• TXD1: Pin 20
• USB_DM: Pin 5
• USB_DP: Pin 6
• V_BCKP: Pin 22
• VCC: Pin 23
• VCC_RF: Pin 9
• VDDUSB: Pin 7

1. GPS Signal Reception:
   • RF_IN (Pin 11): This pin is connected to the GPS antenna to receive signals from GPS satellites.
   • VCC_RF (Pin 9): Provides power for the RF signal processing internal to the module.
2. Power Pins:
   • VCC (Pin 23): Main power input for the module.
   • GND (Pins 10, 12, 13, and 24): Ground connections.
   • VDDUSB (Pin 7): Power input for USB connectivity.
   • V_BCKP (Pin 22): Backup power supply for RTC and module configuration retention.
3. Communication Interfaces:
   • UART:
     • TXD1 (Pin 20): Transmits data to a microcontroller $e.g., location data$.
     • RXD1 (Pin 21): Receives configuration commands from a microcontroller.
   • I2C:
     • SDA2 (Pin 18): Serial data line.
     • SCL2 (Pin 19): Serial clock line.
   • SPI:
     • SCK (Pin 16): Serial clock.
     • MISO (Pin 15): Master In Slave Out.
     • MOSI (Pin 14): Master Out Slave In.
     • SS_N (Pin 2): Slave select.
4. USB Interface:
   • USB_DM (Pin 5): Negative USB data line.
   • USB_DP (Pin 6): Positive USB data line.
5. Control and Status Pins:
   • EXTINT0 (Pin 4): External interrupt input, used for waking up the module.
   • TIMEPULSE (Pin 3): Provides a time pulse output $e.g., 1PPS - 1 pulse per second$.
   • CFG_GPS0/SCK (Pin 16): Configuration and clock pin.

1. Location Tracking: U2 is responsible for receiving GPS signals and determining the current location of the pet.
2. Data Communication: It communicates the location data to the STM32 $U4$ via UART $TXD1 and RXD1 pins$. This data might then be processed or forwarded to the SIM800L $U1$ to be sent over a network.

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• GPS Reception: The NEO-6M-GPS is a GPS receiver module that provides location data to the microcontroller by receiving signals from GPS satellites.
• UART Communication: It communicates with the STM32L4 microcontroller via a UART interface.
• Integrated Antenna: The module can support an external antenna through the RF_IN pin for improved signal reception.
• Backup Power: It can use a backup battery to maintain the time and satellite data, allowing for quicker fixes.

• VCC (Pin 23): Main power supply input.
• GND (Pins 10, 12, 13, 24): Ground connections.
• TXD1 (Pin 20): Transmit Data for UART communication.
• RXD1 (Pin 21): Receive Data for UART communication.
• RF_IN (Pin 11): Input for the external antenna.
• VBCKP (Pin 22): Backup battery input for faster acquisition.

• Power Supply:
  • Connect /design/U2 to [Net 25](@design 25) (3.3V rail).
  • Connect /design/U2 to @design net.
• UART Communication with STM32L4:
  • Connect /design/U2 to /design/U4 via [Net 13](@design 13) (GPS_TX).
  • Connect /design/U2 to /design/U4 via [Net 5](@design 5) (GPS_RX).
• Backup Battery:
  • Connect /design/U2 to /design/BT1, and make sure it also has the proper ground connection.

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• PA0 – PA15: Ensure no floating pins, as they can cause erratic behavior.
• PB0 – PB7: Same considerations as PA pins.
• PC14, PC15: Typically used for oscillator; ensure they're handled appropriately.
• PH3: General-purpose I/O pin.

• PA2, PA3, PA9, PA10, PA13, PA14: Connected as GPS_RX, GPS_TX, SIM_RX, SIM_TX, SWDIO, SWCLK (no pull-up or pull-down needed as they are connected to other components).

• NEO-6M GPS: Check for any configuration pins that might need pull-up/pull-down.
• SIM800L: Ensure pins like RST, TXD, RXD are managed correctly.
• 24AA32A-I/ST: EEPROM, check SDA and SCL lines.

1. Unconnected pins on STM32L4: Verify no floating input pins. Add pull-ups or pull-downs if necessary.
2. GPS Module: Ensure no configuration pins like CFG_GPS0/SCK are left floating.
3. SIM800L: Check RST, TXD, RXD, and other control pins.
4. EEPROM (SDA, SCL): Typically, I²C lines need pull-up resistors.

1. STM32L4:
   • PA0 through PA15 and PB0 through PB7: Unused GPIOs should either be configured as analog mode or have pull-up/down resistors in place.
   • NRST: Already managed.
2. GPS Module (NEO-6M):
   • CFG_GPS0/SCK: Needs to be checked.
   • Other pins seem connected as per the schematic.
3. SIM800L:
   • RST: Needs to confirm proper handling (connected to SIM_RST net).
4. EEPROM (24AA32A-I/ST):
   • SDA and SCL: Typically require 10k pull-up resistors for proper operation.

• PA0, PA1, PA4-PA8, PA11-PA12, PA15, PB0-PB7: Consider configuring as analog mode or with pull-up/pull-down resistors if left unused.

• Connect CFG_GPS0/SCK to GND or VCC (based on configuration).

• RST (Reset pin): Connected properly to SIM_RST net.

• Connect SDA to 3V3 via 10k pull-up resistor.
• Connect SCL to 3V3 via 10k pull-up resistor.

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• Microcontroller (U4: STM32L442KCU6): This is the brain of the tracker, responsible for processing and controlling all functions. It interfaces with the GPS and cellular modules.
• GPS Module (U2: NEO-6M-GPS): Provides location data to the microcontroller via a UART interface.
• SIM Module (U1: SIM800L): Enables cellular communication, allowing the pet tracker's location data to be sent to a server.
• Power Regulation (U5: AP2112K-3.3TRG1): Provides 3.3V to the rest of the circuit from the main power source.
• Battery Management (IC1: MCP73831T-2ACI/OT): Manages the charging of the battery $BT1$.

• Power Supply:
  • The system can be powered via USB $J3$ or from a battery $BT1$.
  • The 3.3V regulator provides a stable voltage supply to components that require it.
• Communication:
  • The STM32 MCU communicates with the GPS module using UART. Connect $U4$ (PA2) to $U2$ (RXD1) and $U4$ (PA3) to $U2$ (TXD1).
  • The SIM800L module is connected to the STM32 via UART for communication. Connect $U4$ (PA10) to $U1$ (TXD) (Net 15) and $U4$ (PA9) to $U1$ (RXD).
• Peripherals:
  • An EEPROM (U3: 24AA32A-I/ST) is connected to store data, interfaced via I2C with the STM32.
  • LEDs (LED1 and LED2) are used for indicating the status of the system. They are connected to suitable GPIO pins on the STM32.

• Ground (GND): Common ground connections for the entire circuit to ensure all components are at the same reference voltage.
• There are some nets used for connections, such as the reset line for the MCU and SIM module, provided there are appropriate lines like Net 16 (for SIM_RST).

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• Input Voltage $V_{IN}$: The input voltage range typically needs to be higher than the regulated output voltage, considering the dropout voltage. For the AP2112, the dropout voltage is quite low, allowing for efficient regulation.
• Output Voltage $V_{OUT}$: Provides a steady 3.3V output, which is used in your project to power various 3.3V components.
• Enable Pin $EN$: The regulator will only output 3.3V when this pin is driven high. It allows the regulator to be enabled or disabled to save power when regulation is not needed.
• Ground $GND$: Provides a reference point for the regulator and relates to the system ground.

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1. SIM800L: $8.29
2. NEO-6M-GPS: (Price not listed)
3. TYPE-C-31-M-12: $0.16
4. AP2112K-3.3TRG1: $0.08 (average)
5. 24AA32A-I/ST: $0.50 (average)
6. FTSH-105-01-L-DV-007-K: $2.68
7. ML414H IV01E: $1.43 (average)
8. STM32L442KCU6: $5.97 (average)
9. MCP73831T-2ACI/OT: $0.71 (average)

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Diagram

sher516362

ystar

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• GPS Module: U2 $\text{(NEO-6M-GPS)}$
• GSM Module: U1 $\text{(SIM800L)}$
• MCU: U4 $\text{(STM32L442KCU6)}$
• EEPROM: U3 $\text{(24AA32A-I/ST)}$
• Voltage Regulator: U5 $\text{(AP2112K-3.3TRG1)}$
• Battery Charger: IC1 $\text{(MCP73831T-2ACI/OT)}$
• Inductor: L1 $\text{(22 µH)}$
• Capacitors:
  • C1 $\text{(10 µF)}$
  • C2 $\text{(10 µF)}$
  • C3 $\text{(4.7 µF)}$
  • C4 $\text{(4.7 µF)}$
  • C5 $\text{(1 µF)}$
• Resistors:
  • R1 $\text{(1 kΩ)}$
  • R2 $\text{(1 kΩ)}$
  • R3 $\text{(22 Ω)}$
  • R4 $\text{(5 kΩ)}$
  • R5 $\text{(5 kΩ)}$
  • R6 $\text{(2 kΩ)}$
  • R7 $\text{(1 kΩ)}$
  • R8 $\text{(10 kΩ)}$
• LEDs:
  • LED1
  • LED2
• Diode: D1
• Battery: [BT1](ML414H IV01E) $\text{(ML414H IV01E)}$
• Connectors:
  • [J1](JST Sales America Inc.)
  • J2
  • J3 $\text{(TYPE-C-31-M-12)}$
  • J4 $\text{(FTSH-105-01-L-DV-007-K)}$

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