Design a schematic for a wearable pressure sensing unit with the following components and connections:
Power Supply
JST-PH 2-pin connector (J1) for 3.7V LiPo battery input
TP4056 USB-C LiPo charger module: BAT+ and BAT- connect to J1, OUT+ and OUT- provide regulated output
SPDT slide switch (SW1) between TP4056 OUT+ and the 3.3V power rail (VCC)
TP4056 OUT- connects to GND rail
Add 10µF decoupling capacitor between VCC and GND
Microcontroller
ESP32-S3-Mini module (U1)
VCC (3.3V) to pin 3V3
GND to pin GND
GPIO8 is SDA (I2C data bus)
GPIO9 is SCL (I2C clock bus)
USB-C connector directly on the ESP32 module for programming and serial debug
0.1µF bypass capacitor between 3V3 and GND, placed close to the module
ADC #1
ADS1115 16-bit I2C ADC (U2), I2C address 0x48
VDD to VCC (3.3V)
GND to GND
SCL to I2C SCL bus (ESP32 GPIO9)
SDA to I2C SDA bus (ESP32 GPIO8)
ADDR pin to GND (sets address 0x48)
ALRT pin: no connect
0.1µF bypass capacitor between VDD and GND close to U2
Inputs A0, A1, A2, A3 each connect to a voltage divider junction (see below)
ADC #2
ADS1115 16-bit I2C ADC (U3), I2C address 0x49
VDD to VCC (3.3V)
GND to GND
SCL to I2C SCL bus (ESP32 GPIO9)
SDA to I2C SDA bus (ESP32 GPIO8)
ADDR pin to VCC (sets address 0x49)
ALRT pin: no connect
0.1µF bypass capacitor between VDD and GND close to U3
Inputs A0, A1, A2, A3 each connect to a voltage divider junction (see below)
I2C Bus
4.7kΩ pull-up resistor from SDA bus to VCC (R_PU1)
4.7kΩ pull-up resistor from SCL bus to VCC (R_PU2)
Bus connects: ESP32 GPIO8 — ADS1115 #1 SDA — ADS1115 #2 SDA
Bus connects: ESP32 GPIO9 — ADS1115 #1 SCL — ADS1115 #2 SCL
FSR Voltage Dividers (8 identical circuits)
Each FSR channel has this circuit:
2-pin connector (J_FSRn) for the force sensitive resistor
FSR pin 1 connects to VCC (3.3V)
FSR pin 2 connects to the voltage divider junction node
1kΩ resistor (R_n) from the junction node to GND
Junction node connects to the corresponding ADS1115 analog input
Channel assignments:
J_FSR1 junction → U2 (ADS#1) A0 — Zone Z1 medial heel
J_FSR2 junction → U2 (ADS#1) A1 — Zone Z2 lateral heel
J_FSR3 junction → U2 (ADS#1) A2 — Zone Z3 medial arch
J_FSR4 junction → U2 (ADS#1) A3 — Zone Z4 lateral midfoot
J_FSR5 junction → U3 (ADS#2) A0 — Zone Z5 1st metatarsal
J_FSR6 junction → U3 (ADS#2) A1 — Zone Z6 3rd metatarsal
J_FSR7 junction → U3 (ADS#2) A2 — Zone Z7 5th metatarsal
J_FSR8 junction → U3 (ADS#2) A3 — Zone Z8 hallux
Resistor values: R1 through R8 are all 1kΩ (1000 ohm)
FSR Connector
10-pin female header (J2) that bundles all FSR connections:
Pins 1-8: FSR signal lines (junction nodes for Z1-Z8)
Pin 9: VCC (3.3V supply to FSR array)
Pin 10: GND
Status LED
LED (D1) with 330Ω series resistor from ESP32 GPIO2 to GND for BLE connection status indicator
Board Specifications
2-layer PCB, 50mm x 70mm
All SMD components where possible except connectors and module headers
USB-C port accessible from board edge
Slide switch accessible from board edge
JST battery connector accessible from board edge
10-pin FSR header along one edge for cable exit
Mounting holes at corners (M2)