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alarm clock help? Answered

i want to make an alarm clock that i can either wear or have it wireless.
other info:
headphones would be ok if the device is small enough i can stick it in a headband or somethong
i dont really have any money to spend on on parts so re-purposed stuff is great
no aduino please! (i dont have one)

any advise would be great!


15 Replies

Jack A Lopez (author)2010-09-21

Let's see... wearable alarm clock... Maybe something like this guy's:
Is that what you're looking for?

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cheesewzrd (author)Jack A Lopez2010-09-27

not exactly...
thats kinda... ridiculous! (but funny)

again, something only i can hear (so's to not wake others)

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Jack A Lopez (author)cheesewzrd2010-09-27

Now I get it.  You want an alarm clock only you can hear. It is possible to re-wire the "speaker" on an existing digital watch or alarm clock so that signal goes somewhere else, e.g. to a pair of headphones or earbuds, or whatever. 

Something to consider: the speaker on a typical alarm clock is usually one of those little piezo transucers, which have high impedance, typically >1000 ohm, while on the other hand typical headphone/earbud speakers have much lower impedance, typically 8, 16, or 32 ohm. 

Anyway the difference in impedance means that simply substituting headphones, in place of the existing piezo speaker, this might not work because the alarm driver circuit is expecting a high impedance, and it will be overloaded by a low impedance load.   

I think the easy solution for this impedance problem is simply to put a resistor( maybe 1Kohm, 10K?), in series with the headphones.  Some people might suggest an impedance-matching-transformer, but that part is a little harder to find, and it would probably make the volume at the headphones uncomfortably loud.

Another trick would be to put the resistor in series with the alarm clock's existing piezo speaker.  That is to say it's the same alarm clock hardware, but now it is much much quieter, so that you'd have to have your ear much closer to the clock to hear it.

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cheesewzrd (author)Jack A Lopez2010-10-03

where might you get one of these resistors for say... free?

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Jack A Lopez (author)cheesewzrd2010-10-04

Resistors? I'm surprised you don't have any in your junk box.

But maybe you are unfamiliar with the concept.  A "junk box"
is a box of broken electronic things, which can be maybe be fixed or used for parts, but is otherwise useless.  Ordinary people throw away non-working electronic gadgets, but those of us who realize electronics can often be fixed, or contain parts that can be used to make/fix something else, we put these things into the junk box.

In fact, if you happen to have any family or friends who are ordinary people (the kind of people who throw out broken electronics) you can likely persuade them to give their broken electronics unto you, instead of throwing it in the trash.

Also there are "dollar stores".

I don't know what part of our fair planet you call home, but here in the Former United States there are places called "dollar stores". Basically it's a store that sells junk, and to make the math easy every item they sell costs 1 FUSD (one former US dollar).

I admit shopping at the dollar store is more expensive than dumpster diving, but the  dollar store usually has better selection, and it doesn't vary as much from day to day as the dumpster fare does.  That's the trade off.

Anyway I don't know what exactly you'll be able to find in your neck of the woods, but I've attached a picture of a disassembled FM radio, that I purchased from a dollar store, for $1.00, plus tax. 

The point is this: If you can find a similar deal, then for only $1 you'll have pretty much every part you'll need: the headphones, the headphone jack, and a small assortment of resistors. As a bonus, one of these resistors is the variable kind, also called a potentiometer. In the picture it's the one with the big black wheel on it. Some people call it a volume knob.

The tricky part is of course unsoldering the parts from the board, and re-soldering them in a way that will do what you want them to to.

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cheesewzrd (author)Jack A Lopez2010-10-04

i do have a junk box...
but i cant tell what's what when it comes to resistors (they all look the same to me). ive got tons of stuff from old vcr's etc. how do i know which to use?

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Jack A Lopez (author)cheesewzrd2010-10-04

The little colored bands tell you what value the resistor is. See this instructable:

What did I suggest originally? 1K? That's brown-black-red-gold. Or maybe 10K? That's brown-black-orange-gold. BTW, this is just a guess.  You might have to try a few different values.   If the sound coming out of the headphones is too loud, try a larger resistor.  If the sound is too quiet try a smaller one.

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cheesewzrd (author)Jack A Lopez2010-10-07

if i use one that's too weak, is it possible i can ruin my headphones? (not to mention my ears)

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Jack A Lopez (author)cheesewzrd2010-10-08

I don't know, so I'll guess maybe it is possible to overpower the headphones.  So some precautions are a good idea. 

The most obvious precaution I can think of is to NOT put the headphones directly on/in your ears while testing the circuit. 

If you're worried about breaking the headphones, you don't have to test with your best headphones first.  If you've got the junky dollar-store headphones, test with those first. For that matter it doesn't have to be headphones. You can test the circuit with an old speaker, like from a broken radio, or whatever.  The only requirement is that this speaker have similar impedance to the headphones, 8 ohms, 16 ohms, something like that.

Another precaution might be to start with really big valued resistors, maybe 100K or 1M, and try and see, I mean listen, if you can hear anything at all.

I wouldn't worry too much about overpowering things though.  Whatever combination of resistor and speaker/headphones you pick is certain to be less efficient at turning electrical power into sound, than was the alarm clock's original piezo speaker. 

So it won't be louder than it was before in terms of total sound power. 

However any sound source will be heard louder if you hold it right up to, or inside your ear.  That's why you don't start testing with the headphones on your ears.

Sorry if any of this seems obvious.

BTW, what does your alarm clock look like? And what powers it? A watch battery? A single AA? Something like that, right?

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cheesewzrd (author)Jack A Lopez2010-10-13

i was thinking of using his one...
it has 2 or 3 aaa batteries

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Another trick might be to have the alarm clock activate some other signal that is not sound, like a small vibrating motor. A lot of cell phones have that feature. Of course implementing that will be little trickier.

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jeff-o (author)Jack A Lopez2010-09-22

You've got my vote for Best Answer. LOL.

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Jack A Lopez (author)jeff-o2010-09-22

Thank you for your support! And 911 is still a joke, now more than ever, although maybe not the way Flav was saying it was originally.

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seandogue (author)2010-09-21

You mean like a cheap Dime-Store watch? It'll cost you about $5-10. And the neat thing is that you an wear it right on your wrist, so you can also use it to tell what time it is!

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cheesewzrd (author)seandogue2010-09-26

not quite...
i mean something only i can hear
so i dont wake others up.

but yes a watch is an obvious idea.

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