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Tracker schematics

Wemos D1 Mini

  • IMU
    • - Great but expensive $$$.
    • - Cheap but drifts quite a bit.
    • - Good but plagued with fakes.
    • - Cheap and good performance.
    • - Experimental cheaper MPU9250 equivalent.
  • - Allows for a second motion sensor to be connected.
  • - The device is able to sense the battery life remaining using a 180k resistor.
  • - Allows for usage even when charging, and is a recommended safety measure.

diode direction Note: If you are using the charge diodes the grey band goes on the side representated by the tip of the arrows in the diagram above.

Label GPIO Input Output Description
A0 ADC0 Analog Input No For analog input from 0 to 3.3v and no output.
RX GPIO3 Yes RX pin only High at Boot.
TX GPIO1 Tx pin only Yes High at Boot.
D0 GPIO16 No interrupt No I2C, PWM Used to wake up chip from deep sleep, High at Boot.
D1 GPIO5 Yes Yes Often used as SCL
D2 GPIO4 Yes Yes Often used as SDA
D3 GPIO0 Pulled up Yes Connected to Flash button
D4 GPIO2 Pulled up Yes Connected to built-in LED, High at Boot.
D5 GPIO14 Yes Yes SCLK pin for SPI interface
D6 GPIO12 Yes Yes MISO pin for SPI interface
D7 GPIO13 Yes Yes MOSI pin for SPI interface
D8 GPIO15 Pulled to ground Yes CS pin for SPI interface

Cable layout recommendation for auxiliary tracker

Note that while schematics show SDA and SCL running adjacent to each other, make sure that they are not physically adjacent when running in the auxiliary tracker cable. This is to avoid crosstalk and ensure stable operation of both trackers when cable and allows the extension to safely reach more than 80cm.

Distance for each setup

If you are using a ribbon cable or similar layout, use the following cable layout as a reference:

Ribbon cable I2C layout

If you are using a twisted pair cable or similar layout, use the following cable layout as a reference:

Twisted pair cable I2C layout

Code put together by Carl (, with images made by Lune#0241, NWB#5135, and Reclusious#2022 thanks to the help of the whole DIY community. Doc page integration by Emojikage#3095. Edited by CalliePepper#0666. Thanks to Snapchat_Hotdog#6124 for the testing on the extension lengths.