ESP32 with the Arduino IDE

You need: any ESP32 board, a USB cable, the Arduino IDE 2.x with the esp32 board package, and the PubSubClient library (Library Manager → search "PubSubClient").

In the portal, open My devices → your device and download chertiot_starter.ino. Your token and the broker host are already in it.
Set WIFI_SSID and WIFI_PASSWORD at the top of the file.
Select your board and port, click Upload, then open the Serial Monitor at 115200 baud. You should see WiFi ok, MQTT connecting... ok, and a JSON line every 10 seconds.
Open My dashboard: the Temperature and Humidity charts start moving within a few seconds.

Send real sensor data

The starter publishes random values. Replace the two lines that compute temperature and humidity with a read from your sensor (DHT22, BME280, …) and keep the JSON keys — the dashboard charts are wired to temperature and humidity. Any other key you send appears in Latest telemetry and can be added to a chart.

Troubleshooting

Symptom	Cause	Fix
`MQTT connecting... failed rc=5`	Wrong token	Copy the token again from the device page; it is the MQTT username, password stays empty
`rc=-2`	No route to the broker	Check Wi-Fi; the broker is `chertiot.com` port `8883` (TLS)
Connects, but the dashboard stays empty	Publishing to the wrong topic	The topic must be exactly `v1/devices/me/telemetry`
Data stops after a burst	Rate limit (10 messages/second per device)	Send one reading every few seconds; see Limits