Server Charms Workshop

This is the code and documentation of a workshop we did for the first time at the CFC25 Conference in Hamburg. In our workshop, we create a tiny, portable microcontroller setups (Server Charms), which create their own Wi-Fi network. This network shows up in the Wi-Fi list of nearby devices, inviting curious people to connect with their devices. Once they do, a captive portal opens, leadingto a small webpage – displaying our server charm manifesto. We are running the microcontrollers on recycled vape batteries which means that the code is optimzed for small power source.

Repository Structure

├── sketch
│   ├── sketch.ino
│   └── html.h
│   └── index.html
├── README.md
└── documentation-zine-[date].pdf

documentation-zine-[date].pdf contains a work-in-progress documentation of how to build a server charm, our server charm manifsto as well as a small glossary. It also links to this repository. We will update the zine in the future. sketch.ino contains the code that is flashed onto the microcontroller to open an access point, host a website and to publish it in a captive portal. html.h contains the html code of the website. It is imported into sketch.ino. index.html is an example template for a website. This file is not actually necessary to upload the sketch. You can use it to edit the website but the code need to be copied to html.h to be included.

The Code

Generally, it opens an access point that redirects traffic to a local server at 192.168.4.1 when phones check captive portal URLs. Since this code is optimized for an ESP32 running on small recycled vape batteries, it allows only 4 clients and is set to use low transmission power to prevent high energy spikes.

Changing the SSID

To change the name of the WiFi, change the *ssid value to a name of your choice.

Adding Password Protection

if (WiFi.softAP(ssid, nullptr, 6, false, maxClients))

To:

if (WiFi.softAP(ssid, "your_password", 6, false, maxClients))

Increasing WiFi Range

Change the transmission power from WIFI_POWER_19_5dBm to lower values to save power:

WiFi.setTxPower(WIFI_POWER_11dBm);  // Maximum range

Available power levels: WIFI_POWER_19_5dBm, WIFI_POWER_18_5dBm, WIFI_POWER_17dBm, WIFI_POWER_15dBm, WIFI_POWER_13dBm, WIFI_POWER_11dBm, WIFI_POWER_8_5dBm, WIFI_POWER_7dBm, WIFI_POWER_5dBm, WIFI_POWER_2dBm

Allowing More Clients

Change the maxClients value e.g. to

const int maxClients = 5;  // Allow up to 5 clients

Note that more clients require more energy! So far, the ESP can handle around 5 clients.

Switching Website content

look_around

Simple click-through html site. The index.html page is just to have an page that you can view in the browser. You can edit the website here and afterwards copy the content to html.h before flashing.

const char index_html[] PROGMEM = R"rawliteral(
// Your HTML content here
)rawliteral";

guestbook

Guestbook template with no styling. Here you can play around with the html Strings in the sketch.ino.