Easy and open source
Measure the Transmission Distance of your filament for HueForge in a free and open source manner
Don't want to tinker and solder around? Buy a prebuilt one!
Buy, plug in and go!
Easier isn't possible: Order, wait for the Td-Free to arrive and just plug it in. But as the Td-Free isn't any kind of proprietary BS, you can do anything with it: Modify the firmware, the case or whatever you want!
Buy the PCB, print your case and go!
Buy the PCB with everything soldered on in the store and just print your own case. Assmeble it and you're ready! You only need black filament for the inner parts (2-3 gramms). Choose any color you like for the outer shell or even go fancy with some cool combination between lid and case color!
Tinker the heck out of it!
Buy, plug in and go!
To build the Td-Free, you'll have to get yourself the parts for the PCB or hot glue/duct tape your own stuff together. If you still plan to go with the PCB, getting it in the store is cheaper than self-sourcing the components and the PCB as there's bulk pricing. The schematics and the PCB design can be found in the GitHub repo in form of KiCad files.
Buy the PCB, print your case and go!
You'll probably design your own case when you use your own electronics. But printing it is quite easy when you already got a 3d printer.
Red: Sensor communication error
Yellow: Starting up
Pink: WiFi hotspot activated
Green: Connected to WiFi AP
Aqua: Filament is inserted and being measured
White: Firmware not properly loaded
Assuming you've got the Td-Free built, you can just plug it into normal USB power. At first, the LED should be yellow and should turn pink afterwards. Now, it opens a WiFi-hotspot called "Td-Free". Connect to it and open http://192.167.71.1 in your browser (Make sure it starts with http, without the "s"). Now, you can measure some filament or connect it to your home wifi.
Readings could be off because of multiple reasons:
1. Filament was inserted during startup (don't do that)
2. Assembly is incorrect
3. Sensor part wasn't printed with black filament
4. Filament is too thin (made for 1.75mm)