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Old 01-02-2011, 12:00 AM   #1
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Car Horn Alarm Clock


Im looking to build a Car horn alarm clock. This was done by Kip Kay at http://kipkay.com/uncategorized/worl...t-alarm-clock/ . Now i have taken apart to clock radios and tested the voltage coming out of the - and + speaker leads, however i dont get any voltage! Not even in millivolts.

I personally need this to work! I know it sounds crazy but i need something loud. Has anyone made one of these? Or is any one willing to make one and post the instructions for the rest of us? All i really need is to get the 5-6volts to get the realy to function.

Hope someone finds this fun enough to do!!

Thanks,

Ty
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Old 01-02-2011, 12:41 AM   #2
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Now i have taken apart to clock radios and tested the voltage coming out of the - and + speaker leads, however i dont get any voltage! Not even in millivolts.
While the alarm is ringing? Something is wrong with your measurement method. If your clock uses an actual speaker (rather than a piezo buzzer), then the signal will be AC. Are you measuring in AC mode? It will probably be a few volts.

You will probably need a more advanced means of activating the relay. The speaker signal alone will probably not activate the coil, but it's worth a try. Use a 5V coil relay and see if it works. If not, you could try using a "solid state relay" designed for a 5V input signal, see if that works. Otherwise you'll need to build a little circuit to detect the AC signal at the speaker and control the relay... I would probably use a diode, RC filter, and NPN transistor in an open-collector configuration.

If that doesn't mean anything to you then you should probably find an alarm clock that uses a piezo buzzer inside instead of a speaker, so it will activate the relay directly.
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Old 01-02-2011, 01:28 AM   #3
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Car Horn Alarm Clock


Ok i measured the voltage in ac and it is less than a 1 volt. I am using a cheap $9.99 clock radio that has a speaker from Walmart. Sony ICF-C218.

So if the 5v relay does not work directly how do i go about making the circuit to control the 12volt car horn relay?

A schematic would be appreciated. I am deaf in my left ear and tend to sleep on my right ear! So i can never hear the alarm clock. I picked up some cheap car horns from Harbor frieght and plugged them into my 12v power supply......and would you know it i can hear them!!!!
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Old 01-02-2011, 01:14 PM   #4
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Car Horn Alarm Clock


What probably happens is the voltage goes on off on off on off to give the alarm it's on/off sound so when you're measuring the meter takes a reading at certain intervals and probably occasionally hits a point where it's off. Just a guess though.

A fast relay should do the trick, I'd think.
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Old 01-02-2011, 02:20 PM   #5
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Car Horn Alarm Clock


Get a lamp timer like they use to fool burglars, plug your 12v power supply with the horn attached into it, and set it to turn on at your chosen wake-up time.
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Old 01-02-2011, 10:21 PM   #6
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Originally Posted by carpenterty View Post
So if the 5v relay does not work directly how do i go about making the circuit to control the 12volt car horn relay?
I like the idea of using a timer to turn on the power supply for the horns. Much easier than hacking the alarm clock. Though if it were me, I'd hack the alarm clock.
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Old 01-02-2011, 10:43 PM   #7
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Car Horn Alarm Clock


If you take the signal from the speaker and feed it to a transformer,
Use the transformer in reverse, to step up the voltage.
try a standard 120v to 12v transformer. ( IN REVERSE )
Apply the speaker signal to the 12v winding,
Measure the output on the 240v winding with an ac voltmeter.
If its around 5 volts or more, feed it to a bridge rectifier
then to a filter capacitor.
You should get enough voltage to pull in a small relay.
You might have to experiment with the transformers to find
which one works best.
Remember car horns usually require a hefty power supply.
You will need a car battery or a big supply.

Quote:
Originally Posted by carpenterty View Post
Im looking to build a Car horn alarm clock. This was done by Kip Kay at http://kipkay.com/uncategorized/worl...t-alarm-clock/ . Now i have taken apart to clock radios and tested the voltage coming out of the - and + speaker leads, however i dont get any voltage! Not even in millivolts.

I personally need this to work! I know it sounds crazy but i need something loud. Has anyone made one of these? Or is any one willing to make one and post the instructions for the rest of us? All i really need is to get the 5-6volts to get the realy to function.

Hope someone finds this fun enough to do!!

Thanks,

Ty

Last edited by dmxtothemax; 01-02-2011 at 10:47 PM.
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Old 01-02-2011, 10:48 PM   #8
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Car Horn Alarm Clock


This is actually a helluva idea and should prove to be interesting. I have a thirteen year old that could use one of those things.
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Old 01-03-2011, 01:07 AM   #9
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Car Horn Alarm Clock


You realize there are millions of deaf, simply hard of hearing, or even more simply deep sleepers on this planet that have the same problem? Look for commercial answers first. Google shopping has 220,000 results for "deaf alarm clock."

http://www.iltsource.com/Deaf_Alarm_Clock_s/38.htm
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Old 01-03-2011, 05:42 PM   #10
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Quote:
Look for commercial answers first.
Nawh. It's not the same as building it yourself.
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Old 01-03-2011, 07:03 PM   #11
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Car Horn Alarm Clock


I sure hope OP doesn't live in an apartment or there is anybody else in the house. If in an apartment, I would expect either an eviction or a visit from the police. If there are other people in the house, I would expect a permanent installation of the alarm in a manner that others would no longer be able to hear it.
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Old 01-03-2011, 08:22 PM   #12
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Nawh. It's not the same as building it yourself.
I agree, its not the same as building one yourself. I will look into building a bridge rectifier, any one have a schematic and how to for this?

I appreciate everyones help, however i would have thought someone might have already built one for pratical purposes or just for a prank!
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Old 01-03-2011, 09:11 PM   #13
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Car Horn Alarm Clock


http://www.diracdelta.co.uk/science/...r/image002.jpg

except I just noticed; it should say "DC out", not in.

You can buy them already put together though.
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Old 01-04-2011, 04:13 PM   #14
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Car Horn Alarm Clock


Bridge rectifiers can be bought quite cheap at places like radio shack,
Or if your real keen you can build one with four diodes.


Quote:
Originally Posted by carpenterty View Post
I agree, its not the same as building one yourself. I will look into building a bridge rectifier, any one have a schematic and how to for this?

I appreciate everyones help, however i would have thought someone might have already built one for pratical purposes or just for a prank!
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