The development board

In this course we will use the ESP32 microcontroller from Expressif. As described before the particularly interesting features of this chip are the integrated WIFI and Bluetooth interfaces (and it's modest price especially when bought directly from Chinese sources).

We use a development board with the Microcontroller on it. Development boards are produced by chip producers to show off the features of the chip they want to sell. The chip is connected to some essential external components and the pins of the chip are accessible via pin rows with a standard pitch of 2.54mm which allows the use of the development board on multi purpose bread-boards as we use them during this course. The board also provides USB to Serial Communication conversion which is convenient since PCs/Laptops do not have serial ports anymore.

The ESP32-WROOM module is the silver module on the development board. You see the PCB antenna sticking out at the side of the module. The WROOM module itself contains the Expressif ESP32 processor and some other chips like for example the Flash memory which will hold the programs.

The microcontroller takes its power from the USB interface so that no external powering is needed. USB provides 5V power, however, the ESP32 requires 3.3V as supply voltage. Hence the development board contains the necessary voltage regulator. Since the processor is usually operated with some external electronic components (sensors, actuators, displays, ...) which also need to be powered the development board provides the 5V and 3.3V on some of the board pins so that the voltages can be used to power external components. But only a modest current can be supplied by the on-board power components, hence do not try to pull a lot of current from the power pins (the power converter is designed for the needs of the ESP32 and some small sensors, not to power a stereo amplifier or similar). If the board is not operated with the power coming via the USB cable, these power pins can also be used to provide the corresponding voltage (either 5V or 3.3V BUT NOT BOTH AT THE SAME TIME!!!) to the microcontroller. Of course, if 3.3V is provided there is no 5V coming out of the 5V pin since there is no power converter on the board which can generate 5V out of 3.3V). Care has to be taken when operating components together since some components need 5V powering whereas others need 3.3V. The ESP32 is a 3.3V component, which means that also the Input and Output pins (I/O-pins) are designed for 3.3V logic levels. Applying 5V logic levels to it's input pins might destroy the controller or compromise its lifetime severely. In case 5V and 3.3V components have to be used, so called level shifters have to be used which convert the different voltage level standards from 5V to 3.3V and vice versa. These level shifters exist in the form of small "break-out boards" which also can be used on the bread board. We will not need these in our exercises.

We have 2 different versions of the board. Note that they have different pinouts. Here a picture of the two boards used int the course. The first one features a micro-USB connector:

The second one features a USB-C connector. The power pins are in in different locations. Please double check which board you are using before connecting the wires!

A very important document is the pinout of the microcontroller board. It is shown here for the micro-usb connector version:

And here is the pinout for the version with a USB-C connector:

Please note and remember the following: Not all of the GPIO pins can be used. There are six pins close to the USB connector which are marked with a red exclamation mark. These pins are internally connected to the Flash memory chip (inside the WROOM module, i.e. inside the small silver metal box on the development board). Therefore these pins should not be used. They are only connected to external pins for some expert usage in very special cases. (These pins are not accessible on the board with the USB-C connector)

In addition you should remember that the pins 34,35,36,39 can only be used as input pins. In addition they do not have internal pull-up resistors. (A pull-up resisitor is a resistor with a pretty high value connected to the supply voltage. Such a resistor makes sure that a line is on logic '1' if nothing else is connected. If another device is connected to such a line and drives the line low the line will result in logic '0' since the resistor value is high and the entire supply voltage will drop over the pull-up resistor.)

Please be aware that the location of the power pins are in different positions on both boards! Double check you power connections before you plug in the USB connector

A very good document is the quickstart guide for the EPS32 of the micropython pages [3].

References

[1] The development board
[2] Pinout Diagram DEVKit-C
[3] Pinout Diagram DEVKit-V1
[4] https://docs.micropython.org/en/latest/esp32/quickref.html