2. April 2017

Custom font for OLED display connected to ESP8266 via SPI

Small OLED displays can easily extend the functionality of ESP8266.

I made an experiment with 128×64 OLED display from Com-Four.

The first challenge was how to connect the display to ESP8266. The recommended way for high performance is to use Serial Peripheral Interface Bus (SPI). The advantage of this approach is the speed, the disadvantage is that it will take more pins.

The display could be connected in following way (also described in the example of ESP8266_SD1306 library):

ESP8266 - SD1306
GND     - GND
3V      - VDD
D5      - SCK (also known as CLK)
D7      - SDA (also known as MOSI/DOUT)
D0      - RES
D2      - DC
D8      - CS

If you’re using PlatformIO, just add ESP8266_SD1306 library to dependencies in platfromio.ini:

lib_deps =

Now you can run any example from Squix78 library. The library contains 3 sizes of Arial font: 10, 16 and 24px.

My goal was to display temperature from Observatory in Brno. Retrieving temperature and sending it to MQTT for ESP8266 was quite easy.

#!/usr/bin/env python3

import paho.mqtt.publish as publish

import urllib.request
f = urllib.request.urlopen('http://www.hvezdarna.cz/meteo/lastmeteodata')
content = f.read().decode('utf-8')

items = content.split(' ')

publish.single('/home/monitor/display/0', items[4], hostname='localhost')

I used default Arial 24 font. The problem was that the number was too small and barely readable from a distance. Luckily Daniel Eichhorn published great online tool which is able to generate font of any size for OLED display: http://oleddisplay.squix.ch.

My first attempt was to generate Roboto Light 54px font. It was working, just number 4 was not visible. I discovered a bug in the generator, that too big font will overflow default size of char in the jump table.

After several attempts I’ve found the right font for me DejaVu Sans 52px. This font was far more readable.

The last touch to make the font more readable was to tune down contrast little bit by the command:


I can definitely recommend this type of OLED display. It has good readability even during a sunny day. The code is available at GitHub in LampESP project.

1. December 2016

ESP8266 WiFiManager gotchas

Thanks to PlatformIO it is very easy to add further functionality from libraries to the code for ESP8266. When you need to install library, just start Library Manager from ide and type:

pio lib install WiFiManager

PlatformIO will resolve dependencies and download all necessary stuff. Even better option is to add dependency to platformio.ini file:

platform = espressif8266
board = d1_mini
framework = arduino
lib_deps =

PlatformIO will manage the installation after you save the file. That is very neat.

Then new problems occurred when I started with integration of WiFiManager. Do not take me wrong. WiFiManager is very handy library, but you may experience some tricky issues.

The first problem that I hit was that WiFiManager interface was not visible at port 80. ESP was apparently running in AP mode for configuration, but there was no web interface. This issue was caused by this line in my code:

ESP8266WebServer server(80);

I had web server in the main code before I merged the code from WiFiManager. Web server was serving simple REST API for controlling relay. Unfortunately this construct blocked the port so the AutoConnect web server. The server was not able to bind the port. Solution was simple. It was sufficient to instantiate web server after WiFi was working.

The second problem was that AutoConnect from WiFiManager was always turning in AP mode. I was hunting the problem for several hours without any result. One idea was that WiFiManager is not saving the password. That was not true. Other idea was that the memory is corrupted and reformat would help. Unfortunately it didn’t. I gave up.

That solved the problem. Seriously. I gave up and that solved the problem. I let the device running and then ding. It was online. For some strange reason ESP8266 was not able to establish connection with particular WiFi router at first shot. Then it turned on AP mode and after timeout of Config Portal it connected to the WiFi network. Remedy? Just shorten ConfigPortalTimeout:


The third problem was that Config Portal was not displaying information stored as extra custom parameters. I stored there host name of MQTT broker and other options so they won’t be hardcoded. The problem was caused by WiFiManagerParameter constructed in global scope. Issue was similar the first problem with web server.

Solution was to move construction of WiFiManagerParameter to the method after loading configuration values from file config.json stored on file system.

File configFile = SPIFFS.open("/config.json", "r");
WiFiManagerParameter custom_mqtt_host("mqtt_host", "MQTT host", configMqttHost, 40);

After resolving these issues WiFiManager is working and it is possible to set values for configuration via Config Portal and there is no need to hardcode them anymore.

Original code is stored at GitHub – LampESP branch v0.1. The new version is at Github – LampESP branch master. I made also small refactoring and the functionality was divided into smaller files which resembles modules for better code maintenance.

1. October 2016

Siriel 03 – Instantiate Prefab from C# in Unity

I was playing with idea to extend the game functionality by adding multi-player support early on. There is very nice tutorial Unite 2014 – New Unity Networking in 5.x., but I was missing one detail. How was Sean Riley able to instantiate game object from prefab. I always ended with some kind of exception or failure.

After several attempts to determine the root cause of my problem I stumbled upon this video “28.Unity Prefabs, Instantiate – Unity C# Scripting Tutorial Beginners” – from Charger Games. I was watching very closely and replayed the sequence several times to find the trick.

Here is whole process in slow motion.

1. Create Prefab from some game object. In my case I will focus on instantiating a pear.


2. Create Empty Game Object and add component Script in C#.


3. Open the script in editor.

using UnityEngine;
using System.Collections;

public class LevelControllerScript : MonoBehaviour {

    void Start () {
    void Update () {


4. Define public GameObject, save the code.

using UnityEngine;
using System.Collections;

public class LevelControllerScript : MonoBehaviour {

    public GameObject pear;

    void Start () {
    void Update () {


5. Go back to Unity Editor and watch the magic. 🙂


6. Unity parsed the code and updated fields in Inspector panel. Drag you prefab and drop it into the new slot.


7. Go back to the code and instantiate it.

using UnityEngine;
using System.Collections;

public class LevelControllerScript : MonoBehaviour {

    public GameObject pear;

    void Start () {

    void Update () {
        if (Input.GetKeyDown(KeyCode.Space))

That’s all. It reminds me of Xcode when you had to drag some stuff into sockets to bind it with code.

Here you can test updated version of Siriel.

During publishing this post I discovered issue with Unity that some assets are not properly loaded when switching between build for Desktop and WebGL. Read more at Unity forum about workaround.

14. December 2015

Slides from talk at FI MUNI: C++ and Software Engineering 2015

Slides available in formats: PDFSlideShare

Source code: GitHub/ysoftdevs/cpp-examples

5. May 2015

C language in our world 2015 – slides

Slides available in formats: PDFSlideShare

Source code: GitHub/ysoftdevs/cpp-examples