Tuesday, March 17, 2009

Master caution button complete!

It took me something around four months for designing and building but the button is now complete. It seems a lot of time but you have to think that:
  1. I don't have a CNC machine (and I don't want to buy one because is very expansive)
  2. I wanted to spend as few as possible (what I have found on the net was around 30EUR)
  3. I wanted to use only COTS
I spent most of the time finding the right components to use and made a design. The initial design was published in a post in december. When the project was ready, I bought the two aluminum squared pipes and started building the button with my dremel. A picture was shown in another post in february.

The button at this stage looked very ugly with the 2 big springs and it was also very hard to press because the springs were very hard. But it did its wok. You have to keep in mind that the only visible part is the upper side.
However, at the moment I had to put the leds I discover that there were not enough room in the upper side. Initially I wanted to put the LEDs in the little pipe while the moving pipe is only the big one. This solution was not suitable because the light would have passed from the holes between the pipe making a very noisy reflection. I had no other choice then rework the bigger pipe leaving more room for the LEDs:

As you can see the upper side is now longer. I have also mounted the switch: when the user presses the button, the bigger pipe shift down and presses the switch closing the contact. At this point I made an extraordinary discover: the switch is enough to move the biggest pipe in the original position when I don't press over the big pipe so the two springs are not needed anymore. The movement of the big pipe is very smoot and when the switched is cliked it emits a very nice sound. Unbelievable but is much better then I expected.
I have put screws in the upper side to hold the support for the LEDs. The support is composed of a shape piece of wood divided in 2 horizonthal lines each of which contains an array of 2 LEDs. The red line is at the top and the red at the bottom. After some investigation I have discovered that an output line of the master card can feed 2 LEDs connected in serial without resistance:

The handles in the upper side will hold the button against the frame in the cockpit.
For covering the LEDs, I have bought some white slides to print with my inkjet printer. I have printed the label in dark black leaving the written to appear in negative :

The written has been covered by a piece of plexiglas that protects the label agains my fingers.

I have finally connected the electronics to the master card and made some test to be sure that everything is working. At this point I have mounted the button in the cockpit. This is the view from the rear (internal) side of the cockpit:

And this is how the button appear in my cockpit:
In my opinion the final result is quite good. The movement is very smooth and the sound when I click the button is wonderful. The yellow LEDs are perfect but I would prefer the red ones to be stronger. However the final result is much better then expected.

Finally the cost. I think it cost a total of 12EUR more or less. I still have along piece of the sqaured pipes that I can use for other button. For example the 767 annunciator as a very similar button for the G/S Inhibit button. The same strategy could be used for korry switches but this implementation nedds a lot of space in the back side of the cockpit so it could be difficult to put two of this button enough close one to the other.

There are a lot of technical issues that I did not talk about in this post of course. If you are interested in the project, want the exact measurement or any other clarification feel free to send me an email or post a comment in the blog.

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