ESP32-C3 SuperMini with 0.42 inch OLED display

Monitoring the ESP32-C3 serial port

If you have PlatformIO installed, the monitor function autoselects the port and baud-rate:

(penv) michiel@Delphinus:~/...> pio device monitor
--- Terminal on /dev/ttyACM0 | 115200 8-N-1
--- Available filters and text transformations: debug, default, direct, esp32_exception_decoder, hexlify, log2file, nocontrol, printable, send_on_enter, time
--- More details at https://bit.ly/pio-monitor-filters
--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H
00:00:09.005 WIF: Connect failed as AP cannot be reached
00:00:13.190 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...
00:00:16.471 WIF: Connect failed as AP cannot be reached
00:00:17.494 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...
00:00:20.776 WIF: Connect failed as AP cannot be reached
00:00:22.798 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...

If you have miniterm installed, you have to choose the serial port:

(penv) michiel@Delphinus:~/...> pyserial-miniterm

--- Available ports:
---  1: /dev/ttyACM0         'USB JTAG/serial debug unit'
---  2: /dev/ttyS0           'n/a'
---  3: /dev/ttyS1           'n/a'
---  4: /dev/ttyS2           'n/a'
---  5: /dev/ttyS3           'n/a'
(... many more ...)
--- 32: /dev/ttyS30          'n/a'
--- 33: /dev/ttyS31          'n/a'
--- Enter port index or full name: 1
--- Miniterm on /dev/ttyACM0  9600,8,N,1 ---
--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
00:00:17.494 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...
00:00:20.776 WIF: Connect failed as AP cannot be reached

Setting the correct Wifi properties

You will have to enter a backlog command in the Platformio monitor or miniterm as follows (and concluding by pressing the enter key):

backlog ssid1 Fritz; password1 xxxMySecretPasswordxxx

Problem is, that you do not see anything when typing it. So, it is easier to just copy it from elsewhere and paste it in. Just paste it in the terminal window. The device will answer with a line "CMD: " and your typed text.

(penv) michiel@Delphinus:~/...> pio device monitor -b 115200
--- Terminal on /dev/ttyACM0 | 115200 8-N-1
--- Available filters and text transformations: debug, default, direct, esp32_exception_decoder, hexlify, log2file, nocontrol, printable, send_on_enter, time
--- More details at https://bit.ly/pio-monitor-filters
--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H
00:06:33.410 WIF: Connect failed as AP cannot be reached
00:06:34.434 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...
00:06:39.740 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...
00:06:43.022 WIF: Connect failed as AP cannot be reached
00:06:44.046 WIF: Connecting to AP1 J&E-2.4G in mode HT20 as tasmota-BA0CD4-3284...
00:06:46.928 CMD: backlog ssid1 Fritz; password1 xxxMySecretPasswordxxx
00:06:46.977 RSL: RESULT = {"SSId1":"Fritz"}
00:06:47.177 RSL: RESULT = {"Password1":"xxxMySecretPasswordxxx"}
00:06:47.328 WIF: Connect failed as AP cannot be reached
00:06:49.001 WIF: Connecting to AP1 Fritz in mode HT20 as tasmota-BA0CD4-3284...
00:06:51.183 APP: Restarting
ESP-ROM:esp32c3-api1-20210207
Build:Feb  7 2021
rst:0xc (RTC_SW_CPU_RST),boot:0xc (SPI_FAST_FLASH_BOOT)
Saved PC:0x40381d16
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fcd5820,len:0x98
load:0x403cc710,len:0x824
load:0x403ce710,len:0x2204
entry 0x403cc710

00:00:00.001 CMD: Using USB CDC
00:00:00.001 HDW: ESP32-C3 v0.4
00:00:00.017 UFS: FlashFS mounted with 304 kB free
00:00:00.024 CFG: Loaded from File, Count 23
00:00:00.026 SER: Set to 8N1 115200 bit/s
00:00:00.026 SER: HWCDC supports 115200 bit/s only
00:00:00.030 QPC: Count 1
00:00:00.072 BRY: Berry initialized, RAM used 5667 bytes
00:00:00.084 Project tasmota - Tasmota Version 15.3.0.1(faf9067-lvgl-haspmota)-3.3.7(2026-02-23T16:57:17)
00:00:01.001 WIF: Connecting to AP1 Fritz in mode HT20 as tasmota-BA0CD4-3284...
00:00:03.362 WIF: Connected
00:00:03.616 HTP: Web server active on tasmota-BA0CD4-3284 with IP address 10.0.3.75

So, now we can access the Tasmota UI in a web browser at http://10.0.3.75.

This also means that we can now enter Tasmota commands at the console - no need for a wired connection any more!

Setting a secondary SSID

You can also set a secondary wifi address as follows:

backlog ssid2 Fritz; password1 xxxMySecretPasswordxxx

Timezone

Look up the commands here: https://tasmota.github.io/docs/Timezone-Table/

I live in Europe/Brussels zone, so for me this is:

Backlog0 Timezone 99; TimeStd 0,0,10,1,3,60; TimeDst 0,0,3,1,2,120

The result is:

20:24:43.208 CMD: Backlog0 Timezone 99; TimeStd 0,0,10,1,3,60; TimeDst 0,0,3,1,2,120
20:24:43.211 RSL: RESULT = {"Timezone":99}
20:24:43.214 RSL: RESULT = {"TimeStd":{"Hemisphere":0,"Week":0,"Month":10,"Day":1,"Hour":3,"Offset":60}}
20:24:43.218 RSL: RESULT = {"TimeDst":{"Hemisphere":0,"Week":0,"Month":3,"Day":1,"Hour":2,"Offset":120}}

MQTT

Set the MQTT properties in the Tasmota UI in the browser, and you will see this in the terminal:

20:28:10.531 MQT: Attempting connection...
20:28:10.552 MQT: Connected

Device name

In the console, enter the commands:

FriendlyName1 Hans
Devicename Hans
Hostname hans

You can now access the device at this URL, instead of using the IP-address: http://hans/.

Template

The initial (empty) template is: {"NAME":"ESP32C3","GPIO":[1,1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,1,1,1,1],"FLAG":0,"BASE":1}.

In the Tasmota UI in the browser, go to Configuration -> Module. Configure the GPIOs:

Setting the teleperiod

The console in the Tasmota web-UI shows measurements from sensors as soon as they arrive. Independently, at a certain interval called the “teleperiod”, a Tasmota device reports its status and measured values to other devices or platforms (often via MQTT).

By default, this interval is 300 seconds (5 minutes). You can adjust this interval, but it cannot be less than 10 seconds. For me, 300 seconds is a bit long, so we change to 30s:

20:01:38.067 CMD: teleperiod 30
20:01:38.071 MQT: stat/tasmota_BA0CD4/RESULT = {"TelePeriod":30}

Finding the display

The command to scan the I2C bus finds one device - the OLED display:

21:47:37.101 CMD: I2CScan0
21:47:37.120 MQT: stat/tasmota_BA0CD4/RESULT = {"I2CScan":"Device(s) found on bus1 at 0x3c"}

Setting the driver

Use the universal display driver by entering this command: DisplayModel 17.

We also need a descriptor file SSD1306_70x42_display.ini. Create this file as display.ini in the Tasmota file system.

Show something on the display

If we go to the menu “Tools” and then “Console”, we can enter a command to show a text on the OLED display. First set the mode (mode 0 is default, but anyhow):

19:48:06.225 CMD: displaymode
19:48:06.230 MQT: stat/tasmota_BA0CD4/RESULT = {"DisplayMode":0}

Then try to display some text:

19:54:17.434 CMD: DisplayText Hello world
19:54:17.489 MQT: stat/tasmota_BA0CD4/RESULT = {"DisplayText":"Hello world"}

Show the measured temperature on the display

In this example, we presume we have a DS18B20 temperature sensor connected to the module.

The display should update whenever a new value of the temperature is measured by the DS18B20 sensor. We will implement this in the programming language Berry, by uploading a file named autoexec.be to the Tasmota filesystem. We can use the following function to show the measured temperature value with some Berry code. Add the following to the autoexec.be here:

var oldvalue = 5000
def updatetemp(value)
    if (value != oldvalue)
        tasmota.cmd("DisplayText T=" .. value .. " C")
        oldvalue = value
    end
end
tasmota.add_rule("DS18B20#Temperature", updatetemp)