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/!\ Vorläufig / Preliminary, work in progress /!\




STM32F103 Boards

From company STMicroelectronics there is a powerful low cost ARM®-based 32-bit MCU with 64 or 128 KB Flash, USB, CAN, 7 timers, 2 ADCs, 9 com. interfaces, named STM32F103x8 (64 KByte Flash ROM) and STM32F103xB (128 KByte Flash ROM).

It is interesting that some (most?) STM32F103x8 also have a 128 KByte Flash ROM, explained later.

There are 2 popular boards (3 - 5 EUR) on the market (Ebay, banggood.com, etc.):

  • STM32F103C8T6 Small System Board Microcontroller, nick name Blue Pill.

  • STM32F103RCBT6 ARM Cortesx-M3 Leaf Maple Mini Module.

Unfortunately boards delivered from China have usually very little documentation for the usage.

I like to explain the usage with the Arduino IDE (version 1.8.5).

  • Benefits:

    • Low cost (about 24 EUR, if more than one is build)
    • Small size (3D printed housing)
    • Battery powered (LiPo 18650 cell)

      • Integrated charge circuit
    • Development under Arduino IDE
  • Drawbacks:

    • If you allow a push signal in a MQTT App on a Smartphone, it empties quickly your battery.

    • If you want to have a small housing, you need a 3D printer
    • You need a lot of background knowledge about software

/!\ A mouse click on a picture will expand the picture for better viewing.

/!\ A mouse click on a source program will show the listing in a new window with colour coding.

ESP32 Breakout Board


  • CPU clock: Standard 80 MHz
  • RAM: 520 KB RAM
  • Flash: external 4 MB
  • I/O: 26 pins
  • Temperature sensor: range of -40°C to 125°C
  • Hall sensor

/!\ The pinout of the ESP32Dev Board and the Wemos LoLin32 are different.


Let's come to the details:

  • Supply voltage, analog: 3.3 V

  • Reference voltage: nominal 1.1 V, span: 1.0 - 1.2 Volt, see here

  • Offset: the ADC has an offset voltage of 0.1 V.

  • Voltage Scaling: Espressif tell about attenuation. The highest usable attenuation is 6 dB = divider factor 2. The maximum attenuation is 11 dB (software default), but it is not linear, and needs a lookup table for using it.

See on the right side the picture. The jumper can be replaced with an mA meter for measuring the standby current.

Links #1. Then you need the Hardware Extension ESP32, which can be installed with:

Parts List

  1. WeMos® LOLIN32 V1.0.0 WiFi + Bluetooth Board, https://www.banggood.com Product ID: 1164252, or https://de.aliexpress.com

  2. 100Pcs Mini Micro JST 2.0 PH 2Pin Connector Plug With 120mm Wires Cables, 3 EUR, https://www.banggood.com Product ID: 1147298

  1. Arduino Software IDE download (Integrated Development Environment), actual version 1.8.5.

  2. Hackaday - Wemos LoLin32 ESP32 module review

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-- RudolfReuter 2018-05-03 18:02:24

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STM32F103Board (last edited 2018-05-23 12:53:25 by RudolfReuter)