Before you get into the fun, I'd recommend doing a quick firmware update. All you need for that is a Windows or Linux PC with any Chromium based browser. Do the update here.
Your Td-Free should light up in white first, then switch to yellow and finally to purple. The purple means that it has opened a hotspot named, you guessed it, "Td-Free". Connect to it with any device and open http://192.168.71.1 in your browser. Make sure it's http, not https! Once you got that site opened up, insert some filament and you should see the td displayed on your screen!
You can connect your Td-Free to your wifi network so that you don't have to connect to the hotspot manually. To do that, open the website of your Td-Free up and click the small Wi-i config link at the bottom. There, you can enter your wifi credentials. Once you click save, your Td-Free resets. If the LED turns green after startup, it has successfully connected to your wifi, but if it should turn purple, it was unsuccessful and the hotspot is back on. TO access is now over your home network, just find its IP address somewhere in your router.
If you visit http://YOUR_TD_FREES_IP/settings (Or click on "Wifi Config", then "Further Settings"), you can change the equation used to calculate the Td value. But only play around with it if you know what you're doing, otherwise you'll be messing up your measurements beyond usable. But if you do so, the default values can always be seeen and set on the page.
Firstly, this integration has some prerequisites:
1. You have a spoolman server running on HTTP, not HTTPS.
2. Your spoolman server doesn't have any authentication.
3. A custom field set up in spoolman for filaments. Key: "td", Name: Whatever you want ("TD"
makes sense), Type: "Float"
To get started with the Spoolman integration, go to "Wifi Config", then "Further
Settings". You'll get to the settings page where you can enter your spoolman URL, but
there are some limitations at the moment: Authentication and HTTPS aren't supported
(yet). So enter your spoolman url starting with http:// and then your IP and the port,
but no trailing slash!
Once that's done, you go back onto the main page where you can measure the filament. To now
save it automatically to spoolman, you'll have to insert some filament and then click on
"Show averaged data". Once the reading is done, a new button labeled "Save to Spoolman" should
pop up. You can click that button and enter the filament ID. If you now get redirected back
onto the measurement page, it saved the data successfully!