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:


Hustle Time said…
Good job man, although that sounds scary as hell!
Nissy said…
I didnt know those sprinkler solenoid valves worked with air. Where did you get the whistle from? You could use an old LPG gas cylinder for extra air reserve.
Pete said…
Hi Nissy, Yeah they can work with air. I got the whistle as a present from an ex girlfriend; she purchased it from ebay. it was somewhere around $300.
macona said…
Do you realize how incredibly bad of an idea it is to weld on pressure vessels? That thing is a death trap unless you have it hydro tested. If that tank let loose under pressure it would kill you.
John said…

oh, you're no fun. anyhoo, pete, excellent setup, well done. keep up the good work
Mark said…
"oh, you're no fun"

Look, genius - plenty of people have been killed by damaged pressure vessels. You're right, it is no fun. Neither is dealing with people who are absolutely convinced of their own infallibility - and given how quickly you dismissed macona's comment, I suspect that you are dangerously close to that.

If you knew anything about welding, you would realize that the tank has been weakened. It needs to be stress relieved and then tested at a far greater pressure than the compressor can attain.

Cool project, but please be careful! If nothing else, put it in your basement where there are concrete block walls. Point the welded end into a corner, and bolt the tank down to the concrete so that it can't take off like a rocket.
Pete said…
The tank was welded by a certified aircraft welder friend of mine. In general, I am very safety conscience and did not have any fear of failure after pressure testing the tank. I also wear my seat belt when driving.
jgarland79 said…
I'm working on a project to make my doorbell send me a text message when it's rung. I have easy access to the doorbell transformer and I made a circuit using a bridge rectifier, 5v regulator, 1000uf cap, and a 5v relay that gets triggered when the bell is rung. I would have used an opto isoloator, but Rat Shack didn't have any.
dbeierl said…
Did you do your pressure testing of the completed tank with water or air? What pressure did you test to?
Pete said…
Pressure tested with air, under water to 130 PSI. I would have gone higher but that is all I had available. And this compressor will never get that high so it should be fine.
dbeierl said…
Water to retain the pieces if it blew, you mean?
Pete said…
No, water to see air bubbles escaping mainly, but you are right, the water will slow down any shrapnel that may arise. And hot water too to raise the temperature, thus the pressure just a bit too.
dbeierl said…
My father used to do hydrostatic testing of quarter-scale models for submarine parts.

The point of using water to test with is that when the device begins to yield you simply stop adding water. Since the water doesn't have any significant energy stored up on compression, the part failure doesn't proceed to completion.

Situation is entirely different with a compressive medium such as air (or in the case of submarines, the failure of the ocean to stop trying after the Thresher began to collapse). The device will violently explode or implode.

I'd seriously suggest you re-think your testing strategy -- hydrostatic testing to I believe twice working pressure is the normal way. Pressure vessels are considerably more dangerous than car springs or garage-door springs, both energy-storage devices which have killed their share of people.

I'm also leery of welding on a pressure vessel without at the very least first consulting the regulatory body that approved it originally. Fatigue resistance is one of the factors that may have changed, and a simple hydro test won't find that. In my youth a number of large airliners fell out of the sky because the fatigue-inducing character of the compression/decompression cycles wasn't sufficiently understood, and the aircraft that turned into a convertible in Maui a few years ago had the same problem -- because its flights were so short it racked up far more than the usual number of cycles. My sister rode on that a/c the previous day incidentally, though she wasn't in first class which was the area that lost its roof.
Pete said…

I get what you are saying but I don't think the level of concern is warranted here.

Two other notes: A: water is a highly compressible fluid. This is why non-compressible fluids ie brake fluid has foil film under the cap - to keep humidity in the air out.

B: we engineers use a factor of safety of 1.5 which I am pretty close to.

Also, meh.
Mr said…
Water is NOT compressable!!!
There is no water in brakefluid because it would start boiling from hot brakes (if you make a fullstop from let's say 50 mph your brakes will almost glow). And if it boils you have air in the system: bad idea!
Pete said…

Water IS compressible however, I doubt I would be able to convince you of this scientific fact. I suggest googling it up and letting them convince you of this widely known physical property of h20 instead.
Mekon said…

>Water IS compressible...

I've checked Google for that scientific fact and as far as I can see, it's going to exhibit negligible compression under the test procedure outlined by dbeierl.

As far as I can tell, for practical purposes, Mr is right in saying that water is not compressible. It certainly seems very far from a 'highly compressible fluid'.

I'm happy to be proven wrong, and if you can post up references that support your opinion, I'll be rather less worried for your safety.
Pete said…

I'm having a pretty hard time understanding your refusal to admit to the physical properties of water. What you call my "opinion" is actually scientifically based observations.

I do not care to indulge your fantasies. You can read any book that I can. Or don't, I'm really not that worried what you do.
dbeierl said…
@Pete --

> water is a highly compressible fluid.

Certainly it is. However speaking approximately an increase of ten bar (~150 psi) will reduce the volume of fifty liters of water by about 11.5 ml, every single one of which will come rampaging out when the tank fails. [/sarcasm]

> This is why non-compressible fluids ie brake fluid has foil film under the cap - to keep humidity in the air out.

Ermm...DOT 3 or DOT 4 brake fluid is extremely hygroscopic. It must be kept dry not because a small volume of water has any great physical effect but because it increases the vapor pressure i.e. lowers the boiling point of the brake fluid. Brake fluid works better when it's not boiling for exactly the same reason that I'm recommending hydrostatic rather than pneumostatic testing.

> we engineers use a factor of safety of 1.5 which I am pretty close to.

I'm curious what your engineering discipline is exactly?

>Also, meh.

Lad, in all seriousness you should go to sea. It will either teach you humility or kill you, whichever comes first. If you are a professional (licensed) engineer this might save you from killing a bunch of people later by.
dbeierl said…
@Mr -- right church, wrong pew. :-)

It truly is compressible, but volume change per increment of pressure is quite small. As pressure is increased to extremely high levels, nine (IIRC) different forms of ice can be produced -- check it out. I seem to recall that Ice IX has a melting point of around 450F but don't quote me on that.

And when brake fluid boils, what you get is brake fluid vapor, the brake fluid equivalent of steam.
dbeierl said…
@Pete --

>I'm having a pretty hard time understanding your refusal to admit to the physical properties of water. What you call my "opinion" is actually scientifically based observations.

Yes, it is. However I'm having an equally hard time understanding your refusal to admit to the existence of powers of ten. Very uncharacteristic behavior for an engineer.

Smiling, but not fooling...
dbeierl said…
@Pete --

In case you're a software engineer, you might want to check out the history of the Therac-25 radiation treatment machine. Here's a place to begin, with a teaser quote below.

>Reprinted with permission, IEEE Computer, Vol. 26, No. 7, July 1993, pp. 18-41.

>Computers are increasingly being introduced into safety-critical systems and, as a consequence, have been involved in accidents. Some of the most widely cited software-related accidents in safety-critical systems involved a computerized radiation therapy machine called the Therac-25. Between June 1985 and January 1987, six known accidents involved massive overdoses by the Therac-25 -- with resultant deaths and serious injuries. They have been described as the worst series of radiation accidents in the 35-year history of medical accelerators.[1]
Nelson said…
Holy cow you guys, this is turning into a super-nerd feeding frenzy. How about "calculated risk" and the fact it's not in any of y'all's basements? The dangers expressed here are very real, I think we all know that, but so is getting out of bed in the morning. Good job Pete, looks like a fun concept and project.
dbeierl said…
@Nelson --

>looks like a fun concept and project.

Hey, it's a great hack, no question about that. Although running on compressed air is a bit whimpy, they don't sound the same as on steam. ;-)

My personal preference would be for an actual fog signal (compressed air by design) or ship's horn, but that's just me. If I did *any* of those things where I live the neighbors would get pretty excited.

Darn -- now you've got me thinking about one using a whistle buoy as the output device. That would be lots safer, have all sorts of cool mechanical interface, make a great lawn ornament and have a volume control. (As a sailor, I really admire whistle buoys. They'll sound in a flat calm if there's the slightest bit of swell, they get louder and louder as the weather kicks up and will shriek like a lost soul in heavy weather as the whistle overblows and goes up an octave. And they depend on impedance mismatch to work. See the whistling buoy section at .)
Pete said…

I can't really argue with anything you said there. but I think @nelson is right, calculated risk should be considered. I also think we are saying the same things I am just more confident in the welds than you are. Hence the previous "meh"
dbeierl said…
@Pete --

>I can't really argue with anything you said there. but I think @nelson is right, calculated risk should be considered. I also think we are saying the same things I am just more confident in the welds than you are. Hence the previous "meh"

Spoken like a gentleman. I don't agree with you but I definitely respect your calm answer.

And as I said to @Nelson, it's a great hack. One thing I'm curious about -- does the Ty-rap on the whistle bell affect the sound noticeably?
Pete said…

The ty-wrap may affect the sound. I was concerned about that in the beginning but it sounds fine, the tywrap is pretty far up the bell so I am sure that helps. Also if you were curious, I tywraped it and put a bit of tape on the plunger because I took the spring and valve out of the whistle.
Mekon said…

>I do not care to indulge your fantasies.

I'd ask for clarification on what these were - but I suppose you don't want to play.
Mr said…
It is barely compressable, especially not at the pressures used in this project:
@40MPa you will only see a decrease of volume of less than 2 %

So stop patronizing me; you are worst than Dilbert.
Mr said…

But when you have water in the brakefluid...well it's boiling point is much lower than the fluid.
That's the reason why it should be changed regularely.
Pete said…

I dont know who "Dilbert" is unless you are referring to the cartoon.

You also need to remember you typed:
>Water is NOT compressable!!!

And you have to know this is wrong. Your point about

>It is barely compressable, especially not at the pressures used in this project

Is not really right; I know what you meant to say but, water is just as compressible at 100 psi as it is at 1000 psi.

Also, just as a blanket statement, as dbeierl correctly pointed out, hydrostatic testing with fluids 'less' compressible than air have an inherent safety advantage if something ruptured. Pressure is pressure if it is air or another fluid, the concerns about safety on my tank testing after wit was welded by a professional welder can be laid to rest as I tested it under water in a stainless steel basin with me around the corner. I'm not sure what else to say at this point.
jgarland79 said…
I just wrote a blog entry about how I made my twittering doorbell.
Mr said…
Well, I do need to say I was wrong about the "not" part and I am sorry if I haven't admited that before. I just had to say something against the statement that it is highly compressible.
But I don't mind to be proven wrong.

And forgot to say: cool project anyhow. If I have time to do it I would love to use the whistle from a steamboat ;-)
Pete said…

I'm glad you like the project; it was just a quick afternoon project to blow off a little steam, hiyo!!
jgarland79 said…

I'm using some javascript I found online to post code on my blog. Take a look at the source code on my blog.
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