user-1: Yesterday I review several years old question with zero answers, voting to close them, which started a debate with perl1234 and gre_gor.
I voted with this explanation:

I'm voting to close this question as off-topic because it's a year old
  question with no answers.

And perl1234 commented:

not being answered is not a valid reason to close a question. I've
  answered questions that were years old. Just because nobody had an
  answer at the time the question was asked doesn't mean it should be
  closed. The sad thing is that if you would just make a little effort
  to look at these questions you're trying to close you would have found
  valid reasons for closing many of them

Well, I'm really wanting to close them because they are low quality post, but that is subjetive criteria, and I thought better to backup that with a objective parameter. Hence, "one year old, no answer".
Of course, not every year old, no answer question is a low quality post. That's why I read everyone one of them and vote to close the most evident culprits. 
I think this a best place to explain what I'm doing and reach a community consensus about how to proceed.
Rationality
The problem with Arduino SE is too many low quality posts, which is evident when you also visit other sites, like Electrical SE or Bicycle SE (long time member there).
There are several markers that identify a low quality post:

First post by a newly create user.
From user that never returns to Arduino SE for a year or more.
No answers, no comments.
No sketch, no schematic, no product identification, poorly written question.
No effort in finding a solution (Arduino SE, Google).
Obvious lack of minimal training in electricity and/or programming.
Demands for complete solution (sketch and/or schematic).

If a question has had no answer for a year or more, it will never have it. There is no point in keeping that question in the site, because even the OP has no interest in the answer.
How to deal with it
The problem is that low quality post isn't one of the reason for closing post, and the other reasons are not fit for the purpose.
A too broad question can be restricted. An unclear what you are asking can be clarified. An off topic can be migrated, and low quality post generally are not duplicated, nor opinion-based. 
A low quality post is beyond redemption. There is noting you can do to improve it. They aren't even wrong.
And the question is: What we do to filter out low quality post?

user10794: If you want to work together on this, you can make crafted searches (in the search box at the top of the page). For example:
answers:0 closed:0  isanswered:no votes:0

That shows a whole lot of unclosed questions with no answers and no votes. They might be candidates for:

Trying to answer them
Down-voting
Improving the question
Asking for clarification
Voting to close

You can also add a date range, eg.
created:..2017-01-01 

That shows questions created earlier than 2017.

user612: You can't close a question because it doesn't have answers, but you can and should vote to close a question if it has been long abandoned by the asker in a state which makes it unanswerable - and especially if they've failed to respond to comments requesting clarification.
Naturally not having answers (or having only terrible ones) often follows from being unanswerable.  But the closing has to follow from the rule violation of posting and then failing to correct an unanswerable question, not from the community's disinterest in answering.

user972: What perl1234 meant was, that you should not close question just because they are old and with no answers, because it doesn't mean it's low quality.
Unless they are actually low quality (no effort, too broad, unclear, gimme the codez, etc.), there is nothing wrong with them being left open.
I am not against closing old low quality question, if they are actually bad, just use a valid reason for the close vote.


First post by a newly create user.  
From user that never returns to Arduino SE for a year or more.  
No answers, no comments.


These by itself are not valid reasons to close it.


No sketch, no schematic, no product identification, poorly written question.


This can be closed as unclear.


No effort in finding a solution (Arduino SE, Google).


This can be closed as too broad.


Obvious lack of minimal training in electricity and/or programming.


This can be closed as unclear or too broad, depending if he can't explain what he wants or he expect from us too much.


Demands for complete solution (sketch and/or schematic).


This can be closed as too broad.

You also seem to have been a little bit sloppy in seeing what is a question without an answer.
This question had an answer by OP edited into the question. I edited that one out of the question and into an answer.
And this question doesn't look like low quality to me. The problem could be replicated with the provided code (assuming it actually does what he says) and a solution could be posted.
Also, if you want to discourage low quality questions, you should not answer them. If you give them what they want, they might come back with another low quality question, even if their previous question was closed.

user10794: How about voting the question down? That is what voting is for. You could also attach a comment explaining why you did it. That might encourage others to vote it down. With enough downvotes it will be closed.

If you feel strongly enough about it you can flag it for moderator attention, as a very low quality post. Then we can close it.


If I flag this post ... will you close it?

Let's not double the work moderators have to do by first asking if we will close something if you flag it, and then waiting for a reply, and then flagging it. :) If you feel strongly enough just flag it and see what happens. 
In that particular question's case the question isn't really all that low quality, and in any case you can't flag questions as very low quality (only answers). (Low quality is for gibberish answers, not just ones that don't answer the question).
The design of Stack Exchange is that it should be self-moderating. That is you, the users, can moderate to a large extent by voting to close, or voting a question down (something you can do without a rep penalty). Moderators are there for extreme cases like insults, spam or things that need to be dealt with quickly.
If only one person down-votes a question, it can't be too bad, right? But if 5 down-vote it then it gets closed. (Caveat: I can't find a reference that proves that particular point, but I think enough down-votes will close a question).
See https://stackoverflow.com/help/privileges/vote-down
Another alternative for you is to edit the question and improve it.

I am sympathetic to what you are trying to achieve here. A while back I went through old questions and voted-to-close or downvoted them. If we don't do that we end up with a lot of junk questions with no answers. I think what will happen is, if you down-vote, and comment, the question gets bumped to the home page, and then others may look at it and also down-vote it, so you can get community consensus on them. :)

-1: <p>Yesterday I review several years old question with zero answers, voting to close them, which started a debate with perl1234 and gre_gor.</p>

<p>I voted with this explanation:</p>

<blockquote>
  <p>I'm voting to close this question as off-topic because it's a year old
  question with no answers.</p>
</blockquote>

<p>And perl1234 commented:</p>

<blockquote>
  <p>not being answered is not a valid reason to close a question. I've
  answered questions that were years old. Just because nobody had an
  answer at the time the question was asked doesn't mean it should be
  closed. The sad thing is that if you would just make a little effort
  to look at these questions you're trying to close you would have found
  valid reasons for closing many of them</p>
</blockquote>

<p>Well, I'm really wanting to close them because they are <em>low quality post</em>, but that is subjetive criteria, and I thought better to backup that with a objective parameter. Hence, "one year old, no answer".</p>

<p>Of course, not every year old, no answer question is a low quality post. That's why I read everyone one of them and vote to close the most evident culprits. </p>

<p>I think this a best place to explain what I'm doing and reach a community consensus about how to proceed.</p>

<p><strong>Rationality</strong></p>

<p>The problem with Arduino SE is too many low quality posts, which is evident when you also visit other sites, like Electrical SE or Bicycle SE (long time member there).</p>

<p>There are several markers that identify a low quality post:</p>

<ul>
<li>First post by a newly create user.</li>
<li>From user that never returns to Arduino SE for a year or more.</li>
<li>No answers, no comments.</li>
<li>No sketch, no schematic, no product identification, poorly written question.</li>
<li>No effort in finding a solution (Arduino SE, Google).</li>
<li>Obvious lack of minimal training in electricity and/or programming.</li>
<li>Demands for complete solution (sketch and/or schematic).</li>
</ul>

<p>If a question has had no answer for a year or more, it will never have it. There is no point in keeping that question in the site, because even the OP has no interest in the answer.</p>

<p><strong>How to deal with it</strong></p>

<p>The problem is that <em>low quality post</em> isn't one of the reason for closing post, and the other reasons are not fit for the purpose.</p>

<p>A too broad question can be restricted. An unclear what you are asking can be clarified. An off topic can be migrated, and low quality post generally are not duplicated, nor opinion-based. </p>

<p>A low quality post is beyond redemption. There is noting you can do to improve it. They aren't even wrong.</p>

<p>And the question is: What we do to filter out low quality post?</p>
 10794: <p>If you want to work together on this, you can make crafted searches (in the search box at the top of the page). For example:</p>

<pre><code>answers:0 closed:0  isanswered:no votes:0
</code></pre>

<p>That shows a whole lot of unclosed questions with no answers and no votes. They might be candidates for:</p>

<ul>
<li>Trying to answer them</li>
<li>Down-voting</li>
<li>Improving the question</li>
<li>Asking for clarification</li>
<li>Voting to close</li>
</ul>

<p>You can also add a date range, eg.</p>

<pre><code>created:..2017-01-01 
</code></pre>

<p>That shows questions created earlier than 2017.</p>
 612: <p>You can't close a question because it doesn't have answers, but you can <strong>and should</strong> vote to close a question if it has been long abandoned by the asker in a state which makes it <strong>unanswerable</strong> - and especially if they've failed to respond to comments requesting clarification.</p>

<p>Naturally not having answers (or having only terrible ones) often follows from being unanswerable.  But the closing has to follow from the rule violation of posting and then failing to correct an unanswerable question, not from the community's disinterest in answering.</p>
 972: <p>What perl1234 meant was, that you should not close question just because they are old and with no answers, because it doesn't mean it's low quality.</p>

<p>Unless they are actually low quality (no effort, too broad, unclear, gimme the codez, etc.), there is nothing wrong with them being left open.</p>

<p>I am not against closing old low quality question, if they are actually bad, just use a valid reason for the close vote.</p>

<blockquote>
  <ul>
  <li>First post by a newly create user.  </li>
  <li>From user that never returns to Arduino SE for a year or more.  </li>
  <li>No answers, no comments.</li>
  </ul>
</blockquote>

<p>These by itself are not valid reasons to close it.</p>

<blockquote>
  <ul>
  <li>No sketch, no schematic, no product identification, poorly written question.</li>
  </ul>
</blockquote>

<p>This can be closed as unclear.</p>

<blockquote>
  <ul>
  <li>No effort in finding a solution (Arduino SE, Google).</li>
  </ul>
</blockquote>

<p>This can be closed as too broad.</p>

<blockquote>
  <ul>
  <li>Obvious lack of minimal training in electricity and/or programming.</li>
  </ul>
</blockquote>

<p>This can be closed as unclear or too broad, depending if he can't explain what he wants or he expect from us too much.</p>

<blockquote>
  <ul>
  <li>Demands for complete solution (sketch and/or schematic).</li>
  </ul>
</blockquote>

<p>This can be closed as too broad.</p>

<hr>

<p>You also seem to have been a little bit sloppy in seeing what is a question without an answer.<br>
<a href="https://arduino.stackexchange.com/q/24470">This question</a> had an answer by OP edited into the question. I edited that one out of the question and into an answer.<br>
And <a href="https://arduino.stackexchange.com/q/31365">this question</a> doesn't look like low quality to me. The problem could be replicated with the provided code (assuming it actually does what he says) and a solution could be posted.</p>

<p>Also, if you want to discourage low quality questions, you should not answer them. If you give them what they want, they might come back with another low quality question, even if their previous question was closed.</p>
 10794: <p>How about voting the question down? That is what voting is for. You could also attach a comment explaining why you did it. That might encourage others to vote it down. With enough downvotes it will be closed.</p>

<hr>

<p>If you feel strongly enough about it you can flag it for moderator attention, as a very low quality post. Then we can close it.</p>

<hr>

<blockquote>
  <p>If I flag this post ... will you close it?</p>
</blockquote>

<p>Let's not double the work moderators have to do by first asking if we will close something if you flag it, and then waiting for a reply, and then flagging it. :) If you feel strongly enough just flag it and see what happens. </p>

<p>In that particular question's case the question isn't really all that low quality, and in any case you can't flag <em>questions</em> as very low quality (only answers). (Low quality is for gibberish answers, not just ones that don't answer the question).</p>

<p>The design of Stack Exchange is that it should be self-moderating. That is you, the users, can moderate to a large extent by voting to close, or voting a question down (something you can do without a rep penalty). Moderators are there for extreme cases like insults, spam or things that need to be dealt with quickly.</p>

<p>If only one person down-votes a question, it can't be too bad, right? But if 5 down-vote it then it gets closed. (Caveat: I can't find a reference that proves that particular point, but I think enough down-votes will close a question).</p>

<p>See <a href="https://stackoverflow.com/help/privileges/vote-down">https://stackoverflow.com/help/privileges/vote-down</a></p>

<p>Another alternative for you is to edit the question and improve it.</p>

<hr>

<p>I am sympathetic to what you are trying to achieve here. A while back I went through old questions and voted-to-close or downvoted them. If we don't do that we end up with a lot of junk questions with no answers. I think what will happen is, if you down-vote, and comment, the question gets bumped to the home page, and then others may look at it and also down-vote it, so you can get community consensus on them. :)</p>
