Using LED's in cars....Dropping Voltage

[King George]

Goodday!

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off. I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this. Or do I have to go through the routine of
stepping down transistors....and going from say 18 volts, to 15 to 12
to 9 to 6 and then use a resistor?? Is there a faster and easier way
to get a 5 volt power source off of a 12v line?? Thank you for any
responses!

King George

 

[Rutger6559]

On 4 Mar 2004 16:47:36 -0800, skammone@flemingc.on.ca (King George)
wrote:

Goodday!

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off. I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this. Or do I have to go through the routine of
stepping down transistors....and going from say 18 volts, to 15 to 12
to 9 to 6 and then use a resistor?? Is there a faster and easier way
to get a 5 volt power source off of a 12v line?? Thank you for any
responses!

King George

I'd buy a 3 pin 5V regulator at Radio Shack, and put a resistor in
series with the LED.

12V car goes to 12V input on regulator
gnd car goes to regulator gnd
5V output pin of regulator goes to + pin of LED
- pin of LED goes to resistor
other end of resistor goes to car gnd.

Someone may be able to provide an approx resistor value to use.

Just my approach.

Best of Luck!!

Rick

 

[Rutger6559]

On Thu, 04 Mar 2004 18:53:11 -0600, Rutger6559 <rutger6559@yahoo.com>
wrote:

On 4 Mar 2004 16:47:36 -0800, skammone@flemingc.on.ca (King George)
wrote:

Goodday!

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off. I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this. Or do I have to go through the routine of
stepping down transistors....and going from say 18 volts, to 15 to 12
to 9 to 6 and then use a resistor?? Is there a faster and easier way
to get a 5 volt power source off of a 12v line?? Thank you for any
responses!

King George

I'd buy a 3 pin 5V regulator at Radio Shack, and put a resistor in
series with the LED.

12V car goes to 12V input on regulator
gnd car goes to regulator gnd
5V output pin of regulator goes to + pin of LED
- pin of LED goes to resistor
other end of resistor goes to car gnd.

Forget the above. This'll just keep a LED on draining your battery!
LOL! Sorry, I'm tired.

12V car goes to 12V input on regulator

This is the one line that is wrong. You need to replace the 12V car
wire with a wire on the other side of your radio's power on switch.
You'll need to look at the radio's wiring to find an appropriate one.
Probably the power antenna remote connector.

Again, just my $0.02.

Sorry about the first post I made!

Rick

 

[michael turner]

On Thu, 04 Mar 2004 16:47:36 -0800, King George wrote:

Goodday!

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off.

Why ? I mean isn't it a bit obvious if the stereo is ON or OFF, i.e. when
it's ON, it's usually all lit up and making sounds.

I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this.

Yeh you can just use a resistor to drop the voltage to power an LED.

Or do I have to go through the routine of
stepping down transistors....and going from say 18 volts,

If the car supply is going to 18V, that too high, this is usually caused
by a faulty alternator/regulator.

to 15 to 12
to 9 to 6 and then use a resistor?? Is there a faster and easier way
to get a 5 volt power source off of a 12v line??

If you want a regulated 5V supply, a 7805 type regulator would do the job
perfectly.

Thank you for any
responses!

King George

--
Michael Turner
Email (ROT13)
zvxr.gheare1963@ivetva.arg

 

[King George]

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off.

I want a light like this because when I turn off my cd player i

sometimes forget to turn off the stereo...which effctively drains the
battery of my car. Yes, I know the simple solution would be to use
the remote wire on my head unit, but i like have seperate control over
my four amps (i dont always need them all on) so I have a switch
panel. I want to add LED's so that I can see if, after I have turned
my Head unit on, that I have also remembered to turn my stereo off.
Basically, I am making lighted toggle switches, just in two pieces.

I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this.

Yeh you can just use a resistor to drop the voltage to power an LED.
by using a resistor, is there not a chance of heating up the resistor
and buring everything out? or can I use a resistor to limit the 14

volts or so enough to safely operate the LED?

If you want a regulated 5V supply, a 7805 type regulator would do the job
perfectly.

I was told that if I wanted to drop a say 14 volt line down to a
regulated 5 volts, I would have to use more than just a 7805. The guy

at active electronics said I would need to step the voltage down in
three volts intervals to make sure that I am not going to burn out the
7805. If thta is all it is, I have a whole bunch of those at home
anyways....

Thank you for any
responses!

King George

 

[Don Bruder]

In article <684da311.0403050632.4d39b811@posting.google.com>,
skammone@flemingc.on.ca (King George) wrote:

I was told that if I wanted to drop a say 14 volt line down to a
regulated 5 volts, I would have to use more than just a 7805. The guy
at active electronics said I would need to step the voltage down in
three volts intervals to make sure that I am not going to burn out the
7805. If thta is all it is, I have a whole bunch of those at home
anyways....

"The guy" doesn't know his ass from a hole in the ground. You were told
wrong.

--
Don Bruder - dakidd@sonic.net - New Email policy in effect as of Feb. 21, 2004.
I respond to Email as quick as humanly possible. If you Email me and get no
response, see <http://www.sonic.net/~dakidd/main/contact.html> Short
form: I'm trashing EVERYTHING that doesn't contain a password in the subject.

 

[bj]

"King George" <skammone@flemingc.on.ca> wrote in message
news:684da311.0403050632.4d39b811@posting.google.com...

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off.

I want a light like this because when I turn off my cd player i
sometimes forget to turn off the stereo...which effctively drains the
battery of my car. Yes, I know the simple solution would be to use
the remote wire on my head unit, but i like have seperate control over
my four amps (i dont always need them all on) so I have a switch
panel. I want to add LED's so that I can see if, after I have turned
my Head unit on, that I have also remembered to turn my stereo off.
Basically, I am making lighted toggle switches, just in two pieces.

hi

I hope this isn't going to annoy your neighbours too much, maybe
your battery should go dead now and again ----however previous
advice was crap. You can work an LED from any voltage you
want as long as you limit the current or drop the excess voltage
(however you want to look at it)
For a 14 volt supply you're looking for about about 1000 ohms
resistance in series.You can play about with that value for
brightness

bj

 

[Rutger6559]

On 4 Mar 2004 16:47:36 -0800, skammone@flemingc.on.ca (King George)
wrote:

Goodday!

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off. I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this. Or do I have to go through the routine of
stepping down transistors....and going from say 18 volts, to 15 to 12
to 9 to 6 and then use a resistor?? Is there a faster and easier way
to get a 5 volt power source off of a 12v line?? Thank you for any
responses!

King George

I still say to use the 5V regulator. That way, if you ever want to
add any other digital circuits to your car you've got a nice 5V line
for the TTL logic.

Check out:

http://electronics.howstuffworks.com/digital-electronics4.htm

for a nice description.

HTH!

Rick

 

[Gerry Cohn]

Hi,

Forget the 7805. Use 1K or 1K2 resistor and be done with it.
If you ever want to add any other 'logic' into you car, you will need a much
better quality power supply than just a 7805 anayway.
A simple 7805 solution does nothing for many of the voltage spikes that you
can encounter in an automitive electrical system. These
would create absolute havoc for any 'logic' that may be powered in this way.

HTH

Gerry

"Rutger6559" <rutger6559@yahoo.com> wrote in message
news:17nh405ghud7djckcd231co3mk94frhs2d@4ax.com...

On 4 Mar 2004 16:47:36 -0800, skammone@flemingc.on.ca (King George)
wrote:

Goodday!

I wanted to wire a warning light up in my dash board that tells me
when my stereo is on or off. I know I need to reduce the car's
voltage down to a lower voltage....Is it possible to just use a
resistor to do this. Or do I have to go through the routine of
stepping down transistors....and going from say 18 volts, to 15 to 12
to 9 to 6 and then use a resistor?? Is there a faster and easier way
to get a 5 volt power source off of a 12v line?? Thank you for any
responses!

King George

I still say to use the 5V regulator. That way, if you ever want to
add any other digital circuits to your car you've got a nice 5V line
for the TTL logic.

Check out:

http://electronics.howstuffworks.com/digital-electronics4.htm

for a nice description.

HTH!

Rick

 

[Rutger6559]

On Sat, 6 Mar 2004 19:36:45 +1100, "Gerry Cohn"
<gerryc[AT]qtcts[.NOSPAM].com.au> wrote:

Hi,

Forget the 7805. Use 1K or 1K2 resistor and be done with it.
If you ever want to add any other 'logic' into you car, you will need a much
better quality power supply than just a 7805 anayway.
A simple 7805 solution does nothing for many of the voltage spikes that you
can encounter in an automitive electrical system. These
would create absolute havoc for any 'logic' that may be powered in this way.

HTH

Gerry

Hmm... Interesting point.

Thanks!

Rick