Research Project Help

[guest213]

Hi!
I am looking for a product to complete my king rail caller. I need an alarm clock that can play an MP3 file or CD as the alarm tone and DOES NOT SHUT OFF AUTOMATICALLY when the alarm has been going for a certain amount of time. My current Timex model shuts off after 1 hour. This was not included in the product manual. I was hoping that someone might know of one that doesn't shut off (except manually) or would be willing to test their alarm out. I would really, really appreciate the help!

Thank you!!

 

[KMoffett]

Depending on the alarm clock, you could replace the buzzer with a resistor (silences the buzzer), have the output trigger a flip-flop (causes a permanent change of state), have the flip-flop drive a relay or transistor that powers the player. It will continue playing until you manually reset the flip-flop. Just a block diagram.

Ken

 

[guest213]

Wow! That sounds great but it far beyond my knowledge and skill level. What qualifies the alarm clock to be able to be fixed up like you described? How exactly would one do that? Or where would one find someone that could do that? I'm good with birds but I don't know about rewiring an alarm clock. You've given me hope! Thank you!

 

[ljcox]

You don't even need a flip flop. Just use a relay with 2 contacts. One to close the player circuit and the other to hold the relay.

The relay is operated by a transistor that is turned on by the buzzer circuit.

The reset button should be a "normally closed" type and be wired in series with the hold contact.

I could help you further, but I need to know more about your alarm clock; ie. whether it applies a high to operate the buzzer or a low.

 

[KMoffett]

Agreed!

Ken

 

[guest213]

How do I know if it applies a high or low?

 

[KMoffett]

whether it applies a high to operate the buzzer or a low

If it 's like most battery alarm clocks, the buzzer is just a Piezo element that is driven by a pulsating DC output. The ones I've played with have the Piezo tied between the (+)supply and an open collector transistor or FET. The collector pulls the Piezo to ground at the frequency you hear.

quest123,
Is this battery or line operated clock?

Ken

 

[guest213]

It has a 2 AA battery backup but has an adapter (output DC 10V 1100mA). I'd tell you more about the inside parts but I just stripped the last screw.

 

[guest213]

Ok! We got the screw out and now we can take a look at the inside. Looks complicated to say the least. Should I post some pictures?

 

[Vizier87]

Yeah, do post them.

 

[guest213]

Pictures of the alarm clock!

 

[ljcox]

If it 's like most battery alarm clocks, the buzzer is just a Piezo element that is driven by a pulsating DC output. The ones I've played with have the Piezo tied between the (+)supply and an open collector transistor or FET. The collector pulls the Piezo to ground at the frequency you hear.

Ken

Yes, I agree, a NPN transistor or N channel FET that switches ground is the most likely.

I could not see anything that looked like a buzzer in the photos.

Have you located it?

Do you have a multimeter? If not, can you buy a cheap one or borrow one?

Do you have anyone who can give you advice, such as an electronics teacher at a college, TV serviceman, etc.?

If not, we should be able to guide you anyway, but it would be much easier for you if you could obtain some advice in person.

 

[guest213]

Well, I've got a conglomeration of fellas who have some knowledge. Maybe some step-by-step instructions that I could show them and see what they think??

 

[ljcox]

1. you need to locate the buzzer.

2. locate a ground point such as the sleeve of the earphone jack - if it has one.

3. connect the - side of your meter to the gnd point.

4. measure the voltage on both sides of the buzzer (without it buzzing).

5. start the buzzer buzzing and measure the voltages again.

Let me know the results and I'll advise you further.

Note that digital meters take some time to make a measurement, so it may not be possible to measure the pulsing voltage (but try anyway). It depends on how fast the buzzing is and the type of buzzer.

An analogue meter will measure the average voltage due to mechanical inertia.

Do you have any resistors? If not buy say a 1k, 4.7k & 10k.