Red Comet ESP32

Description

Our first hooray into the ESP32 world! We weren’t convinced with ESP32 (or it’s predecessor ESP8266) until a custom design client forced us to design an ultra low power wireless data logger based on the EPS32. We initially felt that the reset behavior upon waking up from deep sleep were weird and unconventional. But after diving deep while designing the custom board, that was when we thought what we have been missing all this while. There are tonnes of ESp32 boards out there and some are very well designed too. But, we never found one that is ultra low power and can be powered by various type of primary or rechargeable batteries. We believe that certain battery chemistry fit better in certain application and no single battery type could be best for everything.

Specifications:

• Compatible with Arduino IDE using ESP32Arduino core
• Module:
  • ESP32-WROOM-UE (IPEX connector) or ESP32-WROOM-E (integrated PCB antenna)
  • 4 MB SPI flash
  • ESP32-D0WD-V3 embedded, Xtensa® dual-core 32-bit LX6 microprocessor, up to 240 MHz
  • 448 KB ROM for booting and core functions
  • 520 KB SRAM for data and instructions
  • 16 KB SRAM in RTC
• Operating voltage: 3.3 V
• Low quiescent current (0.075 μA) on-board 3.3 V 400 mA buck-boost switching regulator
• Ultra low power:
  • Rechargeable battery version: minimum 13.0 μA in sleep mode with input at 3.6V
  • Non-rechargeable battery version: minimum 10.0 μA in sleep mode with input at 3.6V
• Power source:
  • Auto power switching between power source applied on the VBAT, VIN or USB
  • External DC source range: 1.8 – 6 V
  • Option to use various battery type, cell combination and chemistry such:
    • Rechargeable: 3xAA NiMH, LiFeFO4, Li-Ion/Pol
    • Non-rechargeable: 3xAA (alkaline, lithium), 3V CR123A lithium, lithium-thionyl chloride (Li-SOCl2), lithium-manganese dioxide (Li-MnO2)
• On-board battery charger:
  • CN3082 battery charger IC that supports multi-chemistry battery including Li-Ion/Pol, NiMH, & LiFeFO4
  • Input to charging circuitry is solar panel optimized akin to MPPT (charge current reduces when solar panel voltage reduces to prevent total collapse of input voltage)
  • 195 mA maximum charge current
  • Yellow indicator LED for charging status
  • Battery charger circuitry not mounted for non-rechargeable battery version
• Red indicator LED connected to pin IO2
• USB-serial interface through CH340C with auto-reset to enter bootloading mode
• USB type-C reversible connector for robust and long lasting usage
• JST PH 2.0 mm battery connector
• Battery power monitoring on pin IO35
• 900 mil in between 2 breakout headers – suitable for breadboard usage
• Dimension:
  • IPEX connector: 25.4 mm x 50.8 mm (1.00″ x 2.00″)
  • Integrated PCB antenna: 25.4 mm x 56.54 mm (1.00″ x 2.23″)
• FR-4 1.6 mm 4-layer PCB with ENIG surface finish
• RoHS compliant: Yes!

Documentation:

• Schematic
• Design files on Github
• Getting started guide