I know this isn't *typically* an audio question - but it has to do with
a display that I'm wiring for my amplifier (to check the temperature).

The display I'm using runs on a range of 5 to 12 volts (with a
suggested typical voltage of 9), and I'll be running it off of the car
battery. I know that a direct (switched, of coarse) line from the
battery would eventually blow this since a car battery can get up to
14+ volts... I know that a resistor or two would/could solve my
problem. What I don't know, and am hoping that someone here does, is
what rating this/these resistors would need to be. Anyone?

~Mister.Lull

A resistor won't decrease the voltage, but the amperage.


--
Francious70

Mister.Lull wrote:
I know this isn't *typically* an audio question - but it has to do with
a display that I'm wiring for my amplifier (to check the temperature).

The display I'm using runs on a range of 5 to 12 volts (with a
suggested typical voltage of 9), and I'll be running it off of the car
battery. I know that a direct (switched, of coarse) line from the
battery would eventually blow this since a car battery can get up to
14+ volts... I know that a resistor or two would/could solve my
problem. What I don't know, and am hoping that someone here does, is
what rating this/these resistors would need to be. Anyone?

A single resistor inline will only limit the current. You'd need to use
two resistors in a voltage-divider setup, but then you'd need to know
the current draw of the display to properly select the resistor values.

A better solution, if you're that concerned about it, would be a basic
one-chip voltage regulator, such as a 7809
(http://www.national.com/pf/LM/LM78L09.html)


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The current draw is only 6 - 10 mA... that help?

In article .com, "Mister.Lull" wrote:
The current draw is only 6 - 10 mA... that help?


Some displays need an isolated supply, but since this is only temperature
I'm sure it will be OK. A vehicle can get up to 16 volts. Any equipment
must be designed to handle peaks of that plus spikes. If this is going to stay on
all the time you certainly don't want to draw any more current. Even
a few milliampers is enough to drain weak batteries, but that 9 volt
regulator sounds like the the best option. You could also use a 9 volt zener
diode across the meter and only use a single dropping resistor of 250 ohms.
That would draw 20 ma. at 14 volts nominal charge rate. However,
if you just use two resistors of 350 ohms each, tap off the center to get
at least 5 volts minimum. The dissapation would be over a quarter watt
between them. The simple way. Use two unequal resistors.
This is a compromise. Use 600-700 ohms on the top side, and 350 on the bottom
ot thereabouts.

greg

....Yes, the LM78L09 would be the best option.

Does anyone know where I can get just 1 of them at a physical location
(near Seattle) ?

I'm starting this whole thing tomorrow night...

Ideas?

Negative for Radio Shack

Radio Shack DOES have resistors, if anyone wants to clarify the options
for that for me...

Remember, I'm only half stupid - I know how to wire the voltage
regulator but I'm completely lost on resistors. So I need to know how
to wire resistors as well as which ones I'd need to use...

~Mister.Lull

Mister.Lull wrote:
Negative for Radio Shack

The 7809 is a somewhat less common unit - they SHOULD have SOME sort of
voltage regulators that fall within your spec, either a 7805 (+5V) or
7812 (+12V), or some equivalent (those are common part numbers, mostly
used by National Semiconductor, if memory serves; there are lots of
others under different manufacturer part numbers).

Go to radioshack.com, search for "voltage regulator" - they list both
the 7805 (catalog# 276-1770) and the 7812 (cat# 276-1771), as well as
the adjustable-output LM317 (cat# 276-1778).


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DUDES!!!

I stopped by Fry's Electronics last night (for those of you who might
not know - they're more or less Outpost.com) and found an equivelant
part!!!

The NTE1902 9Volt output voltage regulator!!!

Problem solved, next stop - stereo bliss.

~Mister.Lull

FRY'S ROCKS!!!

That's where I buy EVERYTHING. Their prices cannot be beat ANYWHERE in the
Seattle area. I go to the one in Renton, I don't know if they even have
another location or what. But it's a TOTALLY FUN STORE!!! It has truly
EVERYTHING you can possibly imagine related to ANY electronic product.

MOSFET

"Mister.Lull" wrote in message
ups.com...
DUDES!!!

I stopped by Fry's Electronics last night (for those of you who might
not know - they're more or less Outpost.com) and found an equivelant
part!!!

The NTE1902 9Volt output voltage regulator!!!

Problem solved, next stop - stereo bliss.

~Mister.Lull

That's the one!!!! I had no idea they'd carry THAT kind of part,
though... I think I found my new favorite gadget store...

~Mister.Lull

equivalent? from NTE? probably not... if their regulators are as bad as
their replacement bipolars, look out.

That's like saying the Yugo is equivalent to a Civic.

JD

Mister.Lull wrote:

DUDES!!!

I stopped by Fry's Electronics last night (for those of you who might
not know - they're more or less Outpost.com) and found an equivelant
part!!!

The NTE1902 9Volt output voltage regulator!!!

Problem solved, next stop - stereo bliss.

~Mister.Lull

What's the worst that can happen?
~Mister.Lull

John Durbin wrote:
equivalent? from NTE? probably not... if their regulators are as bad as
their replacement bipolars, look out.

That's like saying the Yugo is equivalent to a Civic.

JD

Mister.Lull wrote:

DUDES!!!

I stopped by Fry's Electronics last night (for those of you who might
not know - they're more or less Outpost.com) and found an equivelant
part!!!

The NTE1902 9Volt output voltage regulator!!!

Problem solved, next stop - stereo bliss.

~Mister.Lull

Dr. Egon Spengler: There's something very important I forgot to tell you.
Dr. Peter Venkman: What?
Dr. Egon Spengler: Don't cross the streams.
Dr. Peter Venkman: Why?
Dr. Egon Spengler: It would be bad.
Dr. Peter Venkman: I'm fuzzy on the whole good/bad thing. What do you
mean, "bad?"
Dr. Egon Spengler: Try to imagine all life as you know it stopping
instantaneously and every molecule in your body exploding at the speed
of light.
Dr Ray Stantz: Total protonic reversal.
Dr. Peter Venkman: Right. That's bad. Okay. All right. Important safety
tip. Thanks, Egon.


Mister.Lull wrote:
What's the worst that can happen?
~Mister.Lull

VERY NICE!!! :-) Thanks for that (I love that movie)...
~Mister.Lull
Brandonb wrote:
Dr. Egon Spengler: There's something very important I forgot to tell you.
Dr. Peter Venkman: What?
Dr. Egon Spengler: Don't cross the streams.
Dr. Peter Venkman: Why?
Dr. Egon Spengler: It would be bad.
Dr. Peter Venkman: I'm fuzzy on the whole good/bad thing. What do you
mean, "bad?"
Dr. Egon Spengler: Try to imagine all life as you know it stopping
instantaneously and every molecule in your body exploding at the speed
of light.
Dr Ray Stantz: Total protonic reversal.
Dr. Peter Venkman: Right. That's bad. Okay. All right. Important safety
tip. Thanks, Egon.


Mister.Lull wrote:
What's the worst that can happen?
~Mister.Lull

Dead short, lots of stinky smoke. I' go with a TI or motorola 7809.

Chad


"Mister.Lull" wrote in message
oups.com...
What's the worst that can happen?
~Mister.Lull

John Durbin wrote:
equivalent? from NTE? probably not... if their regulators are as bad as
their replacement bipolars, look out.

That's like saying the Yugo is equivalent to a Civic.

JD

Mister.Lull wrote:

DUDES!!!

I stopped by Fry's Electronics last night (for those of you who might
not know - they're more or less Outpost.com) and found an equivelant
part!!!

The NTE1902 9Volt output voltage regulator!!!

Problem solved, next stop - stereo bliss.

~Mister.Lull

I think I'm going to walk on the wild side and keep it in there...
It's freakin' superglued, and soldered into place.
If it blows, the input is fused - I'm not too scared.

~Mister.LivinOnTheWildSide.Lull
Chad Wahls wrote:
Dead short, lots of stinky smoke. I' go with a TI or motorola 7809.

Chad


"Mister.Lull" wrote in message
oups.com...
What's the worst that can happen?
~Mister.Lull

John Durbin wrote:
equivalent? from NTE? probably not... if their regulators are as bad as
their replacement bipolars, look out.

That's like saying the Yugo is equivalent to a Civic.

JD

Mister.Lull wrote:

DUDES!!!

I stopped by Fry's Electronics last night (for those of you who might
not know - they're more or less Outpost.com) and found an equivelant
part!!!

The NTE1902 9Volt output voltage regulator!!!

Problem solved, next stop - stereo bliss.

~Mister.Lull

Mister.Lull wrote:
The current draw is only 6 - 10 mA... that help?



could you not just run it off a 9v battery then?

I could, but that would have to be replaced.
This will never have to be...
~Mister.Lull
metal_flowboard wrote:
Mister.Lull wrote:
The current draw is only 6 - 10 mA... that help?



could you not just run it off a 9v battery then?