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Weird Computer / Amplifier Question

O

oldnewbie

Hi folks,

Hopin' I can again pick some of your brains. Expalanation and question:

I am currently taking a course to prepare for the A+ certification.

I have many years of computer experience, just not much formal training. But I am pretty knowledgable, at least enough to be really dangerous.

Our instructor interviewed each of us on the 1st day. He then partnered experienced people with novices as lab partners. So I have been asigned a lab partner who does not now or has never owned his own computer. BUT, it gets more challenging.

Howard is completely deaf. They provide a sign language interpreter, so it helps.

NOW THE QUESTION:

The beep tones that a motherboard makes when something is amiss. Howard can't hear them. The instructor just kind of shrugged his shoulders and said "Oh, well".

Would this work?: How hard would it be to build a circuit that would connect to the speaker connections on the motherboard and drive a bright LED?

Am I thinkin' right?: Can you connect an op-amp and maybe a 9 volt battery to power such a light or LED (I'll be taking solid state next quarter, so in time I'll know the answer, but in the meantime...).

Any ideas on how to solve this would be greatly appreciated. Howard, btw, is a very smart guy, who works his butt off. I feel a karmic responsibility to do what I can.
 
> Hi folks,
>
> Hopin' I can again pick some of your brains. Expalanation
> and question:
>
> I am currently taking a course to prepare for the A+
> certification.
>
> I have many years of computer experience, just not much
> formal training. But I am pretty knowledgable, at least
> enough to be really dangerous.
>
> Our instructor interviewed each of us on the 1st day. He
> then partnered experienced people with novices as lab
> partners. So I have been asigned a lab partner who does not
> now or has never owned his own computer. BUT, it gets more
> challenging.
>
> Howard is completely deaf. They provide a sign language
> interpreter, so it helps.
>
> NOW THE QUESTION:
>
> The beep tones that a motherboard makes when something is
> amiss. Howard can't hear them. The instructor just kind of
> shrugged his shoulders and said "Oh, well".
>
> Would this work?: How hard would it be to build a circuit
> that would connect to the speaker connections on the
> motherboard and drive a bright LED?
>
> Am I thinkin' right?: Can you connect an op-amp and maybe a
> 9 volt battery to power such a light or LED (I'll be taking
> solid state next quarter, so in time I'll know the answer,
> but in the meantime...).
>
> Any ideas on how to solve this would be greatly appreciated.
> Howard, btw, is a very smart guy, who works his butt off.
> I feel a karmic responsibility to do what I can.
>
I imagine that the small speaker is really a DC transducer that already runs on DC voltage. You should be able to hang an LED together with a series resistor right across it. You'd have to measure the voltage when it fires off, then figure how many volts you need for the LED and what value a resistor you need to drop down the DC voltage. Keep in mind the LED is polarity sensitive, that is it will light in one direction only. You could also use several LED's in series, enough to eliminate the series resistor and this would give you a more noticable display.

GK
 
> I imagine that the small speaker is really a DC transducer
> that already runs on DC voltage. You should be able to hang
> an LED together with a series resistor right across it.
> You'd have to measure the voltage when it fires off, then
> figure how many volts you need for the LED and what value a
> resistor you need to drop down the DC voltage. Keep in mind
> the LED is polarity sensitive, that is it will light in one
> direction only. You could also use several LED's in series,
> enough to eliminate the series resistor and this would give
> you a more noticable display.

If the voltage is sufficient, the LED is a good idea. To avoid needing to check for voltage polarity, you could put two LEDs - one in one direction, and the other in reverse (with respective resistors, if they are needed). One of the LEDs will then always light (the one which has a correct polarity orientation regarding the source signal).


Regards,
Goran Tomas
 
> Hi folks,
>
> Hopin' I can again pick some of your brains. Expalanation
> and question:
>
> I am currently taking a course to prepare for the A+
> certification.
>
> I have many years of computer experience, just not much
> formal training. But I am pretty knowledgable, at least
> enough to be really dangerous.
>
> Our instructor interviewed each of us on the 1st day. He
> then partnered experienced people with novices as lab
> partners. So I have been asigned a lab partner who does not
> now or has never owned his own computer. BUT, it gets more
> challenging.
>
> Howard is completely deaf. They provide a sign language
> interpreter, so it helps.
>
> NOW THE QUESTION:
>
> The beep tones that a motherboard makes when something is
> amiss. Howard can't hear them. The instructor just kind of
> shrugged his shoulders and said "Oh, well".
>
> Would this work?: How hard would it be to build a circuit
> that would connect to the speaker connections on the
> motherboard and drive a bright LED?
>
> Am I thinkin' right?: Can you connect an op-amp and maybe a
> 9 volt battery to power such a light or LED (I'll be taking
> solid state next quarter, so in time I'll know the answer,
> but in the meantime...).
>
> Any ideas on how to solve this would be greatly appreciated.
> Howard, btw, is a very smart guy, who works his butt off.
> I feel a karmic responsibility to do what I can.
>

Hi,

The speaker in the PC is an AC transducer and the current and voltage supplied to beep it are probably not sufficient to power an LED without an amplifier. There is no harm in trying, I just don't think it will work.

You could use an amp such as the LM386 for this and connect the LED in parallel with a reverse diode and in series with a current limiting resistor (330 ohms or so) to the amp output. Search for the data sheet and application notes for sample circuits. This could be powered from the +5 or +12 volt PC supply by plugging into one of the HD power connectors.

I taught PC hardware courses and had deaf students, but their lack of hearing was not a problem because when there is a hardware related boot problem, an error code usually appears on the screen. Exceptions were usually when the memory was not seated properly or the CPU was overheated due to a fan problem, or a video card problem. My students, though they could not hear the beep, could sucessfully trobleshoot. I suppose what I am getting at is that there may not be a problem to overcome.

Neil
 
The speaker output is NOT DC.

You cannot drive an LED with an AC signal such as the tone gen output of the onboard amp. Even if you could, there simply would not be enough voltage swing present.

Your initial speculation was correct, you will need to build some type of op amp to drive the LED.

It may be easier to use a low voltage flashlight bulb, the output will light that, again, provided there is enough voltage.

It's really nice to see you are interested in helping this guy out. Good luck!

-A<P ID="signature">______________
"...How can you be deaf, with ears like that??"</P>
 
> The speaker output is NOT DC.

Right! That slipped my mind ;-(

> You cannot drive an LED with an AC signal such as the tone
> gen output of the onboard amp. Even if you could, there
> simply would not be enough voltage swing present.

You can. IF the voltage is high enough... The LED would act like a half-wave rectifier and it would glow. The frequency of that "beep" is high enough so the LED would probably glow constantly without even adding a capacitor. Voltage would have to be ~1.5V RMS or higher for a standard LED to light up.


Regards,
Goran Tomas
 
> I taught PC hardware courses and had deaf students, but
> their lack of hearing was not a problem because when there
> is a hardware related boot problem, an error code usually
> appears on the screen. Exceptions were usually when the
> memory was not seated properly or the CPU was overheated due
> to a fan problem, or a video card problem. My students,

Moreover, most newer boards have a couple of diagnosis LEDs. Usually there are 4 of them and they represent a 4-digit binary number. If there's something wrong, they will light up a code for a particular error that you easily look up in the manual...

Regards,
Goran Tomas
 
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