DIY Home Improvement Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter #1
Im looking to build a Car horn alarm clock. This was done by Kip Kay at http://kipkay.com/uncategorized/worlds-loudest-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:thumbup:!!

Thanks,

Ty
 

·
Semi-Pro Electro-Geek
Joined
·
3,403 Posts
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.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #3
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!!!!
 

·
Wire Chewer
Joined
·
3,579 Posts
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.
 

·
Registered
Joined
·
39 Posts
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.
 

·
Semi-Pro Electro-Geek
Joined
·
3,403 Posts
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.
 

·
Registered
Joined
·
5,467 Posts
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.

Im looking to build a Car horn alarm clock. This was done by Kip Kay at http://kipkay.com/uncategorized/worlds-loudest-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:thumbup:!!

Thanks,

Ty
 

·
Tileguy
Joined
·
10,705 Posts
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.:)
 

·
You talking to me?
Joined
·
7,551 Posts
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.
 

·
Registered
Joined
·
9 Posts
Discussion Starter #12
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!
 

·
Registered
Joined
·
5,467 Posts
Bridge rectifiers can be bought quite cheap at places like radio shack,
Or if your real keen you can build one with four diodes.


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!
 
1 - 14 of 14 Posts
Top