## Step 3: Check That Everything Fits

There's not much space to play with in this project, so it's important to make sure that you know how you're going to fit everything in.

First of all, check that your LEDs will fit the 3 round tubes on the bottom of one of the 2x4 bricks.  It'll probably be a little too tight at this stage, but almost fit.  That's fine.

Check that your switch and battery holder will fit completely inside the traffic cone - the switch goes in first, and the battery holder will probably need to go in diagonally.

Finally, check that your hose (or other choice of 'pole') fits snugly in the top of the traffic cone.  It might not push all the way in yet - that's OK, so long as it fits the opening.
<p>I made it for my son :)</p>
<p>Hey! I made a modified version for my girlfriends nephew! </p><p>Check it out: <a href="https://www.instructables.com/id/ATtiny85-Traffic-light-toy/" rel="nofollow">https://www.instructables.com/id/ATtiny85-Traffic-l...</a></p>
Can u make me one of these?
Hi,<br><br>why are you not using resistors to limit the current flowing through LED? <br><br>I was searching for ideas how to build traffic lights and that's how I came to your site.<br><br>BR,<br>Tomek
<p>Hi Tomek,</p><p>The coin cell isn't capable of putting out enough current to damage the LED, so a resistor just isn't necessary. You can happily wire an LED directly to a coin cell and it will be fine - do a search for &quot;LED throwies&quot; to see another example that makes use of this fact.</p>
<p>Hi,<br><br>thanks for your reply. So the red LED (with let's say forward voltage @ 1.8V) also doesn't require a current limiting resistor because the battery (3 Volts) is so low current source- correct?<br><br>BR,<br>Tomek</p>
<p>Correct. A typical small LED generally has a max current rating of about 10-15mA. The typical maximum discharge current of a CR2032 is about 4mA - so there's lots of margin.</p>
<p>I've found a great article that explores this topic <a href="http://www.evilmadscientist.com/2009/some-thoughts-on-throwies/" rel="nofollow">http://www.evilmadscientist.com/2009/some-thoughts...</a> <br>it turns out, it's good to use current limiting resistor if you want to have long battery life. Note the current they measured using red LED.</p>
Duplo brings back memories....
Thanks for the praise.<br><br>I knew I wanted to make it as soon as I noticed the perfect pattern of 3 tubes on the bottom of the small bricks, and it was a fun exercise bringing it all together.<br><br>Most important of all, the kids love it!
try a 555 timer not as simple but no programming required
Yeah, I considered a 555, but I happened to have a pile of ATTinies lying around, they're almost as cheap, and their great advantage is the minimal parts count. There's so little space inside the Lego that space was critical.<br><br>The ATTiny is programmed to go into deep sleep when the button hasn't been pressed for a while, to preserve battery life. I think that would also be pretty hard to achieve with a 555-based approach.
Fun idea, I like it!
Very nice!