Introduction: Broken Nose Preventer

Picture of Broken Nose Preventer

There are three doors in my house that open outwards, and I have personal experience how easy it is to walk into the edge of one of them in the dark. After doing this a few times, I decided to build a device for providing a flashing LED embedded in the edge of the door to warn you that it is open.

This is really simple to make, and saves getting blood on the bedroom carpet

Step 1: Step 1. Make the Circuit

Picture of Step 1. Make the Circuit

The circuit came from my stash of ancient electronics relics, I have no idea where it originated. It will run off a single AA penlight dry battery, although I used a bigger C size battery. The original unit has been running in my house 24/7 for around 5 years so far with no sign of giving up yet.

I etched the circuit board myself and soldered the parts to it. I used BC107 transistors for TR1 and TR2, and a 2N3906 pnp transistor for TR3, but pretty much any npn transistors will do for the first pair, and any pnp for the third one. The LEDs I used are 5 volt types, but I’m not sure that they need to be, and I suspect any standard LED (and any colour you like) would work just fine.

Step 2: Step 2. Assemble to the Mounting Plate

Picture of Step 2. Assemble to the Mounting Plate

The LED leads are left long and the LED itself is glued into an alloy plate that is recessed into the edge of the door so that the circuit board just hangs off the LED leads. A space chiseled out of the door behind the plate houses the circuit and battery, there is just enough room inside the door to fit the standard C type torch battery.

The power consumption can be reduced even more if the circuit is switched on and off by means of a pin switch (like the ones used on a car hood to trigger the alarm) embedded in the hinge edge of the door so that when the door is closed the flasher is turned off and uses no juice at all.


DisplacedMic (author)2011-11-03

Yeah - you think you're so clever except one of these nights it will be the Terminator looking at you and not your soft little blinky door light. Then you'll all be sorry for laughing at me and my crooked nose.


If this were like Facebook, I would hit the like button. Hey Instructables you should create a LIKE button.

overblast (author)DisplacedMic2011-11-04

We sent John Connor your address so he could ambush it.

You and your crooked nose are safe with us!

The Cylon Support Network

Madrigorne (author)overblast2011-11-09

You make me sooooo happy.
We also like your crooked nose.

johnfrog (author)2011-11-05

Very cool! Back in remote antiquity (c.1980) there used to be a little IC (LM 3909, I think) that did the same sort of thing - would run an LED forever on a 1.5v battery with only a timing/storage capacitor. Good if you're pushed for space or (like me) too lazy to make PCBs. Nice instructable; brings back old memories! :-)

blister75 (author)johnfrog2011-12-09

I believe it's a 555 timer your thinking of.

dwosullivan (author)2011-11-03

A photoelectric switch would work pretty well here too!
Nicely done.

rvan es (author)dwosullivan2011-11-07

Hate to disagree, but no it wouldn't.

This instructable is only useful at night, when there is little light, exactly the same as when you have the door closed and covering the switch.

dwosullivan (author)rvan es2011-11-07

True. My Bad.
It could at least be used to have it turned off when it sees light, i.e. when the door is open during the day, then the LED would only light when the door is closed or its night time. It would be worthwhile even if using a reed switch so if the door is open during the day the light won't shine.

I guess this is getting more complicated than its worthwhile, Its a great idea, It looks like it works well and the author doesn't seem to have any problem with battery life. well done!

GitarGr8 (author)rvan es2011-11-07

A reed switch would however.

Remag1234 (author)2011-11-03

Obviously you have too much time on your hands. A simple Night Light would do and a hellva lot easier.

grizelli (author)Remag12342011-11-06

Yep, I just retired, so plenty of time to do stuff like this. You ain't seen nothin' yet :-)

Remag1234 (author)grizelli2011-11-06

Good, I'm retired and it's tough because every day is a day off. ;-)

MandingaRes (author)2011-11-06

Buen proyecto grizelli ! y muy buenos proyectos los de tu blog.

(Bien dicho bstevenson1!! Cada uno hace de su tiempo lo que se le canta!!!)

grizelli (author)MandingaRes2011-11-06

Muchas gracias! Keep watching the blog, loads more stuff is coming soon!

lambsb (author)2011-11-06

All usefulness or purpose aside, It is a nice looking circuit and nicely built. As for anyone who might use this to warn of an open door..... (I would prefer blue LED's, they're cool) we always need new excuses to build LED projects. How can you resist? The 3909 IC will flash an led but I prefer to use a 555, you can get many different pulse patterns from it just by changing the rc circuit values.

There is also a circuit from Radio Shacks optoelectronics projects book I use from time to time that is a dual led flasher, that uses 2 2n2222 transistors and I think 2 2n3906's. (Like a school bus or railroad crossing flasher). Maybe useful to someone.

e5frog (author)2011-11-05

There are LEDs with a built in flashing circuit, no need for 13 something components when three is enough. Flashing LED, resistor and battery. Possibly some switch to turn it on/off as well.

Stop walking around in the dark, would probably help.

vroom350 (author)2011-11-04

Simple make LED box with reed switch magnet just put on top door with use double tape without hard hand and/or drill hole. More life save battery when closed the door.

madfreet (author)2011-11-03

Easier still ...just fit a door closer

grizelli (author)madfreet2011-11-03

Not much fun in that though, is there? Unless you can get them with LEDs on? :-)

madfreet (author)grizelli2011-11-03

And doors should be kept closed..(ever heard of fire) not
much fun being burned alive either

madfreet (author)madfreet2011-11-03

Also ...if your staggering around in the darkness...a closed door
represents just as much a hazard as an open
lets consider the stairs...assuming you have stairs that is....
ie darkness, staircase...fall...broken neck....yep id happily
take the open door and broken nose : )....lets have some
LEDS on that staircase please...flashing ones. Now youve just
picked yourself up from the fall down stairs, broken neck takes
your mind of your broken nose...still pich black and you bump into
someone !!! well you get my drift lol...just turn on the light

grizelli (author)madfreet2011-11-04

You must be a mind reader. I already have LEDs installed on every step of the stairs with a PIR to turn them on when it sees a warm body approaching from either the top or bottom of the staircase. I'll post this on here as well shortly. I like LEDS :-)

madfreet (author)grizelli2011-11-04

I see from your pic that you have the danger of
walking out of the window solved lol : )

Javin007 (author)2011-11-03

I need to make one of these for the leg of my damned bed. I've broken my little toe on that thing TWICE already.

BigShotUK (author)Javin0072011-11-03

May I humbly suggest a thin strip of glow in the dark paint?
I know it's not got that tech-cool, but I'm sure it'd do the job.

Javin007 (author)BigShotUK2011-11-03

But then I wouldn't get to use my power tools...

overblast (author)Javin0072011-11-04

So how would you get your power tools to light up when your toe got close?


Let's say you have your saber saw welded to your oak bed leg.

You get too close and it turns on, the sound would alert you of impending pegleg disaster.

This would be great for blind people who couldn't see a red light.

BigShotUK (author)overblast2011-11-04


BigShotUK (author)Javin0072011-11-03

Granted, glow in the dark paint wouldn't need power tools to apply. However, you could use power tools to make a corner cover (L in cross section) painted in glow in the dark paint to do the same job. Also has the advantage of being easily removed with the right adhesive.

Of course you could also just paint the legs in 5 minutes and then use the remaining build time to make something else entirely... and that could be far more power-tool hungry than this. :D

BigShotUK (author)BigShotUK2011-11-03

"...easily removed with the right adhesive."

Make that "If attached with the right adhesive it also has advantage of being easily removed."

vincent7520 (author)2011-11-04

I don't get it.
Why don't you just get rid of your doors. As you've got only three I guess you place is somewhat small : you wouldn't believe the feeling of roominess when you trips the doors of a small apartment !…
OK , I'm joking, but it is true : I don't have doors in my house (except a sliding panel for the bathroom).

EvilRSA (author)2011-11-03

I really like the idea of the a pin switch, and as long as we're talking about drilling through the door to get to the hinge side for the switch, why not drill to the top of the door instead, put the switch there and add a photo cell too, so when the door is open the led only fires when it's dark enough that you wouldn't be able to see the door, and no visible distraction during the day when you can see the door. Plus keeping the switch and photo cell on the top, you wouldn't have to see them either, keeping a nice clean look....actually, you can put all the of the circuit in the top of the door, and just run the LED down the door, and actually combine the LED with the exiting latch that would be a slick and clean look, with extra function.

grizelli (author)EvilRSA2011-11-04

Good idea, especially putting all the electrics in the top of the door and running just the LED in the lock plate. I have to fit another one of these to a french window, thats probably how I will do it, thanks for the suggestion

vidakk (author)2011-11-04

You could also implement a reed switch and put magnet in doorframe, so the circuitry sitches off when door is closed.

frickelkram (author)2011-11-03

Works great!
Low battery voltage leads to more frequent flashes. It is easy to see that the battery needs to be changed. I am using BC547c and BC557c and a high power red led. I used a 470uF capacitor instead of a 100uF. Because the 10k resistors where out of stock I am using 12k, these work as well. The circuit operates from nearly 1V up to 6V. If you go above 3V the flashing frequency gets very low and the led starts glowing right before the flash pulse. Best operation is with 1.5V alkaline cells as grizelli recommended.
I have'nt made any long term test, because I just built it one day ago. It runs on a 1.1Ah NiMH battery since then, without problems.
The way the shematic was drawn reminds me of German magazine called Elektor or Elrad ...

claudiaivonnefranco (author)2011-11-03

Your instruct able made me burst out laughing, I could see myself doing the exact same thing! Thanks for the laugh! Great idea!

XTL (author)2011-11-03

The point of the circuit is efficiency. A simple battery and resistor will not last long at all. Maybe 2 days, as opposed to 5 years.
So simple yes - cheap no...

starlored (author)2011-11-03

Ever heard of a light switch!!!

bowlerhatman (author)2011-10-29

Alternatively, you can buy LEDs with a flasher circuit built into them, with these, you just hook them up to 3v and the flash. An elegant and simple solution though, I like it.

eg_colon73 (author)bowlerhatman2011-11-03

Ther we go! thats what I was taking about. Lest money, smaller and easy to install!

and7barton (author)2011-11-03

What's the point ?
It's gross gross overkill -
One flashing (or otherwise) LED, a tiny battery and a resistor will do precisely the same job.... cost - pennies.......... build time hardly longer than a minute........ no circuit board.

grizelli (author)and7barton2011-11-03

True. However, a) the battery will need to provide 3 volts at least, so you will need at least two cells (may not be room for these inside the door); b) the circuit draws almost no current, and c) how long will your 'tiny battery' last? Mine has been running for over 5 years so far on the same battery, the expected life on a C cell is around 50 000 hours at least.

eg_colon73 (author)grizelli2011-11-03

Actually and7barton is right. I used a LR44 Button Cells(x3) to power a LED for another use. They last a long long time (mine been in use for 3 years atm) very cheap and very easy to use. You only need a LED, the cells and electric tape. But this don't blink. Maybe you can make another using this tech and make it blink. Oh! and btw our new home's doors have something similar meant for the same purpose, this doors well the entire house have Schlage LiNk System, is super cool!!!

anode505 (author)2011-11-03

Wouldn't using a flashing LED be easier?

grizelli (author)anode5052011-11-03

Simpler yes, but you would need bigger batteries to give a high enough voltage to fire the LED - this circuit takes the 1.5 volts of a single cell and boosts it. If you want to fit it inside a door like I did, there may not be enough room for more batteries

tigerbomb8 (author)2011-10-30

you could hack a solar garden light.

Barramundi (author)2011-10-30

could you post the artwork for the PCB?

ilpug (author)2011-10-29

Elegant solution to a problem everyone has encountered.

corsairdude (author)ilpug2011-10-29

Every one but me I guess :) Cancel cancel cancel!!!

About This Instructable




Bio: Trained in mechanical engineering, discovered computers in the late seventies, been collecting junk and making stuff all my life. Recently retired, I now have the ... More »
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