Heartbeat is an Arduino / NodeMCU program that does a periodic web inquiry to execute some HTML/PHP based task. Typically a timer is set for any time between one minute to one day. The Wi-Fi version requires hard-coded SSID and password. An Ethernet version requires a cable.
It can be the basis for DDNS services by getting the web program to compare the calling external IP address to the previously stored address. If it differs the program can the update the DDNS service with the new address.
It can awaken a web program to retrieve a current status and store it on a file for a web query program to process.
