You can Validate your idea with free and paid method:

Free Method
- Post your landing page to forum that related with your product category example:Product Hunt ,Hackers News is ok i think

Paid Method
-You can run ads on Facebook ,Twitter and google Ads with your Coming Soon landing page

or you can run your project on indiegogo and kickstarter to validate your idea plus get your financing if reach your goals

I love landing pages and LaunchRock is one of the best. The beauty of a landing page is there's almost no wrong answer. In other words, use landing pages as a means to gauge how people might respond to you. They enable you to A/B test which basically means you can experiment with slightly different versions of the same landing page to see which gets more traction.

The first question I'd ask you is who is your intended audience? You obviously built a prototype of some sort. If I were to assume you've solved a problem, who did you solve it for? When those people are out searching for a solution to their problem, what are they searching for? How does the conversion sound? How can you use your landing page to insert yourself into that search?

There's not enough room here, but a using a landing page as part of a user onboarding, education, lead gen..... (whatever) strategy is a very good idea. You also may not know some of these answers, so using a landing page will inform you of who is actually interested in what you're offering. You may find it's a different market altogether.

Anyway, just a quick handful of thoughts.

Start promoting on social networks, this could be done for free. You will also need paid adverts on Google (AdWords) and Facebook. Go for CPC/CPM campaigns.

If you need more guidance, then setup a call with me.