audio sensor project design thoughts

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I have a car with a built in CD player. I have installed my previous car's
subwoofer and amplifier into the new car.

The previous CD player had a "remote" cable that turned on the amplifier.
This new one does not. I have been manually turning on the amplifier with a
switch but, I am now looking at ways of sensing the audio coming from the
speakers, and designing a circuit to trigger the amp for the subwoofer.

I recall there was a kit that did this but for the life of me I don't know
where and when I saw this.

I pulled out my multimeter and noted that the speaker terminals are offset
by 6V from the car chassis. Whether the CD player is on or off, I still
measure 6V DC from either speaker terminal to the car's ground. So
obviously, when the stereo is playing, the speaker voltages with respect to
the car's earth fluctuate around the 6V mark.

Analogue electronics is not my strong point. Any pointers?

I was thinking of a really simple circuit using an optocoupler and a 555
timer. The optocoupler diode would be connected to the speaker terminals via
a resistor, and the trigger would set a 555 timer to turn on the amp for a
period of time. If after about 1 minute there was no further trigger, the
amp would switch off.

I thought this would work, but the voltage across the speakers is not enough
to drive the optocoupler LED at low volume directly.

I should mention that I don't like op amps much. Would this be the only
approach?



Re: audio sensor project design thoughts


Holy shit, just hook the amp's remote wire up to an accessories wire, and
wire the power to the battery (fused).
Or wire both pwr/remote to accessories, like mine are.

Wayy too much effort there for a simple result!

For the record, my amps are wired directly off the accessories, with a
bridge between Pwr & Remote on the amps. And i'm only running a 30a fuse
where a 50a should be for the 'main' accessories fuse - no problems
whatsoever so far. Blew a fifty, had a thirty so rigged it up, never got
around to putting the new 50 in as it's working fine.

Basically wired it like that due to the pain-in-the-arse factor of running a
single wire to the amps after i'd put all the trim back in and the dash back
together.

-mark



Re: audio sensor project design thoughts



"mark jb" <nukeleer at internode dot on dot net> wrote in message
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a
back

I was going to do that but I would slightly miss out on some of the
functionality of the radio.
The radio is able to be turned on without the accessories on, and I would
still like the amp to turn on at this time as well. (sorry to be picky)



Re: audio sensor project design thoughts


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Then how about a current sensor on the radio +ve? 'standby' and 'on' will
have substantially different draw levels, should work a treat and be a bit
simpler than the speaker output.

I've got my accessories hooked up to both the ignition and a seperate
switch, so I don't need to leave the keys in for the radio on... perhaps you
would be better off with the switch? didn't bother me all that much when my
amps were hooked up thru a seperate switch, good for h/free phone calls and
the like - quick whack and silence!

-mark



Re: audio sensor project design thoughts


... Second thoughts, why not wire up that convenient switch you have via a
relay to turn the accessories on/off?
Should be cheap, quick and easy to do.

-mark



Re: audio sensor project design thoughts


Does the stereo have a wire for a power aerial, if so use that to power the
amp whenever the stereo is on.
Regards
John


"Heywood Jablome" <reply to thread> wrote in message
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Re: audio sensor project design thoughts


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What about when he's listening to CD?

They generally only have power down them on Radio... at least, all the ones
i've come across have only had power on radio, stock and aftermarket.

-mark



Re: audio sensor project design thoughts


Thanks all for your thoughts. They are all valid thoughts but not suitable
for my needs. I should explain myself a bit more. The player that I have in
the new car is an integrated unit. It has wired in controls on the steering
wheel, and uses the dash display to display the MP3 info and Radio info. The
CD drive is separate and fully moulded into the center console with no
display at all.

The car is fitted with dual air bags, and is only two weeks old, so I don't
want to take the whole dash assembly apart to find out exactly what the
connections are between the screen, steering wheel, and integrated dash
readout are. I have a feeling in any case that this would be time wasted, as
if there was provision for an amp remote, it would have already been wired
out of the console to a place where it could be accessed. The manual makes
no mention of this, so my best bet is that it is not there.

The antenna is a fixed antenna on top of the car, so no possibility of using
an auto antenna wire.

The remote switch that I currently have is not actually a remote switch. It
sits in the boot, so I have to open the boot to turn on the amp (and
remember to turn it off !!)

So since I have the power cables, and speaker connections where I want them
(in the boot), and I have limited means of wiring any more cables, I was
thinking of a system which would simply sense whether audio was being played
through the speakers, and turn the amp on/off accordingly.

While tapping into the accessory wire may be physically possible, I'd prefer
not to, as these new vehicles are quite complex little beasts. There is
excellent functionality built in but adding a trick such as inducing power
down the accessory wire might cause more problems than it solves.  For
instance, currently, if I turn off the ignition with the key, but keep the
key in the ignition, the radio keeps playing. Only when I remove the key
does the radio stop playing. (nice little feature)
Also, as I mentioned earlier, even with no key present, I can still turn on
the radio, and it stays on for an hour. Gone are the days of simple "off"
"acc" "on" states.

Just out of interest, I might state that the power windows have some tricky
little power control features themselves. For instance, they do not move
when the key is out of the ignition, but if you have set them to go up, and
then take the key out of the ignition, they continue to go up till fully
closed. It's not a simple timer. It is all individually controlled by the
onboard computer.

The main thing is that I really would not want to muck with the cables. I
think I have all that is necessary in the boot to make a perfectly
functional system. I just need a sensor circuit that will be on 24/7 that
monitors whether there is audio coming from the speaker connections, and
turns on the amp.

The sensor circuit would of course have to use minimal power. I swear I have
seen this type of kit somewhere. I think it was used to turn on a remote
subwoofer or something. Can anyone remember the source?



Re: audio sensor project design thoughts


What is the car? If the controls are on the steering wheel leave it alone. I
was offered the complete data base of customers of Lexus if I could work
these controls out, as you can imagine, I bent over backwards and contacted
every Lexus repair shop I could find so I could get my hands on the customer
list.

"Heywood Jablome" <reply to thread> wrote in message
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Re: audio sensor project design thoughts


hmmm.. bit of a privacy breach if you would be successful in getting that
list!!

I would be ready to kill someone if I had found out they contacted me by
getting my details from a leaked list of buyers.

-It's a holden barina. The CD player etc... is all standard these days.

I have bitten the bullet and am designing an op-amp circuit now. I don't
know why but I am quite averse to op-amps.  Something about analogue
electronics in general that I detest. Sorry if I offend anyone here but
digital electronics is so nice and black and white!




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Re: audio sensor project design thoughts



"mark jb" <nukeleer at internode dot on dot net> wrote in message
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If his equipment doesnt have a volume control, he should trade it in.

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Re: audio sensor project design thoughts


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to drive the optocoupler LED at low volume directly.

so the amp is not needed at low volume ?

a diode across the opto diode to protect against reverse voltage is also needed

Re: audio sensor project design thoughts



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enough
needed


I'd still like the amp to be on at low volume.

I thought that the opto diode would not need another diode to protect it.
But I'll wack it in anyway, thanks.



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