GTEM ESP32 ATM90E26 SDK v1 – Interfacing


GTEM ESP32 ATM90E26 Energy Monitoring Energy Monitor

ESP32 Interfacing

The ESP 32 interfaces to the ATM90E26 via either:

  • SPI
  • UART (connected to ESP32 UART2)

This is user selectable using the pads on the bottom of the GTEM board. By default, SPI is selected.

The ESP32 interfaces to the AT24C64 EEPROM via I2C. It has an address of 0x50

Flashing and Debugging connection to the ESP32, is via the USB UART (CH340).


The GTEM board has a number of solder pads on the bottom.

Default settings:

  • SPI ATM Interface Enabled
  • Metering Mode L+N
  • CT Clamp Burden Resistor Enabled
  • OLED Pin 1 Ground – Pin 2 3V3
  • SPI CS Open
  • OPTO Pull up Disabled Open
  • User Jumper GP25 Disabled Open

The defaults are shown with a line above the pads to short.


  • 21 SDA I2C. Pulled High via 10K
  • 22 SCL I2C. Pulled High via 10K

  • 12 User GP12 GPIO Strapping Pin. Boot fail if pulled HIGH
  • 13 ATM_IRQ
  • 14 User GP14 GPIO Note: ESP outputs PWM at boot
  • 15 LED BLUE Strapping Pin. Outputs PWM at boot

  • 19 MISO V-SPI
  • 23 MOSI V-SPI
  • 18 SCK V-SPI
  • 5 CS V-SPI. Strapping Pin. Outputs PWM at boot

  • 1 TX0 USB_TXD Debug output at boot
  • 3 RX0 USB_RXD HIGH at boot

  • 17 TX2 TTL_TXD
  • 16 RX2 TTL_RXD

  • 0 GP0 Strapping Pin. Outputs PWM at boot
  • 2 LED LED RED Strapping Pin. Connected to on-board ESP LED
  • 4 ADC 2 CH0 LED GREEN Strapping Pin. Ignore 0 – 0.1V and 3.2 – 3.3V

  • 27 ADC 2 CH7 ATM_WO Ignore 0 – 0.1V and 3.2 – 3.3V
  • 32 ADC 1 CH4 ATM_ZX Ignore 0 – 0.1V and 3.2 – 3.3V
  • 33 ADC 1 CH5 OPTO Ignore 0 – 0.1V and 3.2 – 3.3V
  • 34 ADC 1 CH6 ATM_CF1 input only. Ignore 0 – 0.1V and 3.2 – 3.3V
  • 35 ADC 1 CH7 ATM_CF2 input only. Ignore 0 – 0.1V and 3.2 – 3.3V

  • 36 VP / ADC 1 CH0 PCA DC Supply DCV_IN input only
  • 39 VN / ADC 1 CH3 NTC-10K input only

  • 25 DAC1 User_Jumper With pullup and decoupling cap
  • 26 DAC2 User_Button With pullup and decoupling cap

The below GPIO must be in the following states when ESP32 boots, or it will fail to boot.

  • GP0 High
  • GP3 High
  • GP5 High
  • GP12 Low
  • GP15 High


Important Foot Note.

These Wiki pages are MOVING to the GitHub Wiki.   Simply select a repository pertaining to the board and click Wiki.


Other Details

Further information on this product may be found in our downloads and Wiki pages.  Other technical information and code examples are also shared in our GitHub Pages.  Project information may also be found on

We value our customers and should you have any other questions, please feel free to contact us.

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