Friday, May 14, 2010

Train Whistle Doorbell

For the people who know me, the title of this project will be read as “well that sounds about right”. For the rest of society it may need some modicum of rationalization. To that end, have you ever missed the doorbell ringing? Perhaps you were in the shower or vacuuming the floor. Well, fear no more; you won't miss hearing this one.
I was given this Lunkenheimer steam train whistle as a birthday gift quite a few years ago. I came up with the idea to make it into a doorbell shortly thereafter for pretty obvious reasons, but I was unsure how I wanted to execute the wireless part of it. As you can see here I ended up using an el-cheapo wireless doorbell. This solved a lot of problems for me, not the least of which is that I can let the bell ring for a bit first before activating the steam whistle so my heart remains firmly in my chest rather than being startled to death every time UPS stops by.

Circuit wise, this doorbell came with an led on the front that blinks when the bell is activated. So, when I was designing the circuit in my head, thinking I would have to tap into the circuit board to get a logic signal; turns out I could just make a simple circuit to 'watch' the led; a photo transistor with a 10k pulldown works a treat. The sprinkler solenoid is rated at 24VAC. I don't know why they are AC and they work fine on DC, but it was easy enough to make a power supply that had the 24VAC and 12VDC so I did. The 5v RadioShack relay annoyed me when I found out it was going to draw 83mA and I would need a transistor amplifier. Yeah, not that big of a deal, but I thought I was being clever instead of using one of the 12v automotive relays from the junk box.

I took the spring and valve out of the steam whistle so that it could be operated solely by the sprinkler solenoid. This allows a massive amount of air to be passed through the whistle so “tuning” it was necessary by screwing the bell part in closer to the air escapement. I was hovering over the whistle when I tried out the circuit for the first time and it literally blasted the eye glasses off of my face.

Ear defenders are necessary.

The doorbell has, I think, 7 different rings to it. I settled on the “fog horn”; it cracks me up. It reminds me of Eeyore for whatever reason. Then the train whistle kicks in so it is like the whole thing goes from depressive to bat shit hyper in 3 seconds. For now it does a toot tooooot as you would imagine. It uses up pretty much all the air in the compressor in that short amount of time.

The video can be seen here; sadly the camera cannot pick up how loud it really is. The fact that the entire assembly wiggles when activated should give you a bit of an idea how much air is being passed through it though.

Here is another vid of the doorbell in action.  The whistle is set inside of the house while I activate it from outside.

I am still trying to find a good way to upload code, but for today here it is:
The schematic:

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