How can I replace a watch alarm with a motor?
- Thread starter JC531
- Start date
blocco a spirale
- Joined Jun 18, 2008
- 1,546
Mike, you misunderstood me. I was replying to the OP not you; I know, that you know, the sounder requires an AC signal.
MaxHeadRoom
- Joined Jul 18, 2013
- 28,686
Something to consider, supposedly you will be using an audio signal, 1khz is 1ms cycle duration, the motor would have to be minute to be able to react at this freq.
But if the mechanism was made so the motor could turn continuously while the alarm occurred, there would be less concern of considering reversal inertia etc.
Amplify the audio signal then rectify it?
Max.
But if the mechanism was made so the motor could turn continuously while the alarm occurred, there would be less concern of considering reversal inertia etc.
Amplify the audio signal then rectify it?
Max.
Before you embark on a plan I wanted to see if you understand how motors work.
Did you know that the alarm in your wristwatch and a loudspeaker are also electrical motors? They both convert electrical energy into mechanical motion.
Let us start with a typical 8Ω loudspeaker. It is constructed as a coil of wire placed in the magnetic field of a stationary permanent magnet. When you pass a DC current through the coil, the coil and the attached speaker cone will move a certain distance from its resting position. How much current does it take to move the coil? Have you ever connected a 1.5V battery to a loudspeaker and observed this behaviour? If not, why not try it? Calculate the current flowing through the 8Ω coil from the 1.5V battery.
Now, how would one create a tone from the loudspeaker? To produce a 600Hz tone, you have to move the speaker cone back and forth 600 times each second. You do this by driving the speaker with a 600Hz signal (DC or AC is all semantics at this point).
The sound of the alarm in your wristwatch is created with a piezoelectric transducer, similar to the loudspeaker but works on a completely different principle.
The piezoelectric transducer has infinite resistance but appreciable capacitance. When you connect a 1.5V battery to the transducer the DC current is zero. To create audible sound you have to drive the transducer with an AC signal at the desired frequency, usually above 1kHz. At this point the capacitance of the transducer presents itself as an appreciable load which we call reactance. The bottom line is that the current required to drive a piezoelectric transducer is much less than that required to drive a loudspeaker.
Now we get to the motor. The vibrate motor that you will find in a mobile phone is a super tiny DC motor. Again, it works on the same principle as the loudspeaker with a coil of wire in a magnetic field. How does it work on a DC current? The motor has special mechanical contacts on the shaft of the motor called a commutator. The purpose of the commutator is to reverse the direction of the magnetic field of the coil every time the armature turns 180°. This keeps the armature turning.
The point of this discussion is that a DC motor, like a loudspeaker has relatively low DC resistance and require substantially higher current than a piezoelectric transducer.
Hence you need to consider what power source will be required to drive a motor.
Did you know that the alarm in your wristwatch and a loudspeaker are also electrical motors? They both convert electrical energy into mechanical motion.
Let us start with a typical 8Ω loudspeaker. It is constructed as a coil of wire placed in the magnetic field of a stationary permanent magnet. When you pass a DC current through the coil, the coil and the attached speaker cone will move a certain distance from its resting position. How much current does it take to move the coil? Have you ever connected a 1.5V battery to a loudspeaker and observed this behaviour? If not, why not try it? Calculate the current flowing through the 8Ω coil from the 1.5V battery.
Now, how would one create a tone from the loudspeaker? To produce a 600Hz tone, you have to move the speaker cone back and forth 600 times each second. You do this by driving the speaker with a 600Hz signal (DC or AC is all semantics at this point).
The sound of the alarm in your wristwatch is created with a piezoelectric transducer, similar to the loudspeaker but works on a completely different principle.
The piezoelectric transducer has infinite resistance but appreciable capacitance. When you connect a 1.5V battery to the transducer the DC current is zero. To create audible sound you have to drive the transducer with an AC signal at the desired frequency, usually above 1kHz. At this point the capacitance of the transducer presents itself as an appreciable load which we call reactance. The bottom line is that the current required to drive a piezoelectric transducer is much less than that required to drive a loudspeaker.
Now we get to the motor. The vibrate motor that you will find in a mobile phone is a super tiny DC motor. Again, it works on the same principle as the loudspeaker with a coil of wire in a magnetic field. How does it work on a DC current? The motor has special mechanical contacts on the shaft of the motor called a commutator. The purpose of the commutator is to reverse the direction of the magnetic field of the coil every time the armature turns 180°. This keeps the armature turning.
The point of this discussion is that a DC motor, like a loudspeaker has relatively low DC resistance and require substantially higher current than a piezoelectric transducer.
Hence you need to consider what power source will be required to drive a motor.
I see. I had no idea, this is all new to me and extremely fascinating. For the power source of the motor then, an external battery?
I just took a glance at this thread. http://forum.allaboutcircuits.com/threads/replace-speaker-of-alarm-clock-with-dc-motor.101453/
Some mention to use a sensitive relay. But i'm not sure what that is or how it is used...
Thanks in advance for having patience with my lack of electrical knowledge guys.
I just took a glance at this thread. http://forum.allaboutcircuits.com/threads/replace-speaker-of-alarm-clock-with-dc-motor.101453/
Some mention to use a sensitive relay. But i'm not sure what that is or how it is used...
Thanks in advance for having patience with my lack of electrical knowledge guys.
I was just glancing at the thread out of curiosity.
So the base idea was a watch that, at its most basic functionality, when a countdown hit zero instead of alarming, would vibrate. This would be used during timed exams to allow for pacing (especially when one forgets to check the time).
I had the idea when I took my first SAT and just a few days ago found these:
http://www.testingtimers.com/testing-timers/how-it-works/
and
http://examinator.com/the-examinator-watch/how-does-it-work/
the second one has vibration functionality.
In general the project, more specifically the watch, is something that would go along with pacing and testing strategies. Even if such devices existed, the design of my watch ended up becoming (say it became an actual product) just another type of watch but with improvements to the two mentioned. I had this idea for months before I found those other two watches. After doing some surveys and stuff in school I figured it would be a pretty cool idea to try.
Its because it will be used for testing that it would have to be done on a watch.
So the base idea was a watch that, at its most basic functionality, when a countdown hit zero instead of alarming, would vibrate. This would be used during timed exams to allow for pacing (especially when one forgets to check the time).
I had the idea when I took my first SAT and just a few days ago found these:
http://www.testingtimers.com/testing-timers/how-it-works/
and
http://examinator.com/the-examinator-watch/how-does-it-work/
the second one has vibration functionality.
In general the project, more specifically the watch, is something that would go along with pacing and testing strategies. Even if such devices existed, the design of my watch ended up becoming (say it became an actual product) just another type of watch but with improvements to the two mentioned. I had this idea for months before I found those other two watches. After doing some surveys and stuff in school I figured it would be a pretty cool idea to try.
Its because it will be used for testing that it would have to be done on a watch.
