Can I use Edge 510 as an indoor trainer computer
I'm basing this on my 810 but I assume they're similar.

You can create a new profile for riding on the turbo. For each profile you can select which sensors are used. If you turn off GPS and turn on cadence and speed (and HR if you have it) you can use it indoors. You might need another sensor to pick up wheel speed if you only have a cadence sensor. A combined (speed and cadence) one is around £35 in the UK, not sure what they'd be in Sweden.

I don't have it on me at the moment. If you need more details I'll post instructions based on mine this evening.