I'm trying to hardwire an ipod cradle to my car, and I want to be lazy and skip buying resistors.

Is there a handy 5 volt source somewhere?

 

No.

Do it the proper way. If you're that lazy, get a adjustable universal cig lighter plug, set it for 5 volts and hardwire that to 12v.

 

lazy= money in the long run. Do it the right way.

 

Just get peripheral part # PXP01

Charges and gives you av out. 12v and the price ain't bad either

 

just get some resistors man to go from 12 to 5 volts all you need is a 42ohm and a 58ohm resistor, do some math 12* 42/(42+58) bam you got yourself 5.04 volts. just make sure to run the ground to your chassis!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slowSOHCvtec &raquo;</TD></TR><TR><TD CLASS="quote">just get some resistors man to go from 12 to 5 volts all you need is a 42ohm and a 58ohm resistor, do some math 12* 42/(42+58) bam you got yourself 5.04 volts. just make sure to run the ground to your chassis!</TD></TR></TABLE>

Thats it huh? How much current do you intend to run through these resistors?

I wouldn't recommend using a voltage divider to run anything.

Assume a load of 500mA 500mA*9.36v = 4.68Watts!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Thats one fricken HOT resistor and you didn't even take in to account the tolerance of the resistors.

Once you attach that load, your voltage divider will no longer work the way you intended it to.

You could use a voltage divider with a unity gain opamp and you would be good to go.

buy the 7805 version from http://www.digikey.com would cost you less than $1 plus add shipping. Get the T0-220 version. You will have a regulated 5V.
http://www.st.com/stonline/pro...b.pdf


Modified by nsxxtreme at 3:55 PM 8/8/2006

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">Thats it huh? How much current do you intend to run through these resistors?


Once you attach that load, your voltage divider will no longer work the way you intended it to.</TD></TR></TABLE>

whats ur reason for that? sure once you connect the ipod the voltage may drop slightly but not enough for it to not function, i wouldnt imagein an ipod would use that much current, maybe 200mA or so

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxxtreme &raquo;</TD></TR><TR><TD CLASS="quote">
You could use a voltage divider with a unity gain opamp and you would be good to go.</TD></TR></TABLE>

you want to use this for the purpose of buffering right?


Modified by nsxxtreme at 3:55 PM 8/8/2006[/QUOTE]

all u gotta do is get 10 watt tolerance resistors and your good, or you could just get a buck converter, or a simple DC-DC voltage converter with a 5V output...check micrel's site or TI's, im sure they make one, they are usually good up to 10 amps at least, they ahve sense resistors so you can actually set the current you want and most of them are good from 12-48Vdc, i can even order you one from my work if you want my company deals with them in bulk all the time

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18C_EJ8 &raquo;</TD></TR><TR><TD CLASS="quote">No.

Do it the proper way. If you're that lazy, get a adjustable universal cig lighter plug, set it for 5 volts and hardwire that to 12v.</TD></TR></TABLE>



Ghetto rigging ---&gt; BAD!
Proper Install ----&gt; GOOD!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slowSOHCvtec &raquo;</TD></TR><TR><TD CLASS="quote">

whats ur reason for that? sure once you connect the ipod the voltage may drop slightly but not enough for it to not function, i wouldnt imagein an ipod would use that much current, maybe 200mA or so

you want to use this for the purpose of buffering right?
</TD></TR></TABLE>
Yes you could use the op-amp to buffer the load. You only use a voltage divider to "set-up" the initial voltage. Voltage dividers are bad designs. As the voltage in your car changes so will the output.

(14.4-5.04) = 9.36V this is the amount of votage you are trying to drop across the resistor. 200mA*9.36V=1.872Watts!!!!! That is still a really hot resistor. And you voltage would be jumping all over the place as the load and voltage changes.


The voltage regulator I recommended would cost you probably $2.00 has 3 connections (2 input 1 output) and would deliver 5.00V no matter what the input voltage. It uses a zenor diode reference to set the voltage up. So in a car it will always deliver 5V.

 

why not just get the 12v car adapter and plug it into the back of the cradle..?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sony224422 &raquo;</TD></TR><TR><TD CLASS="quote">why not just get the 12v car adapter and plug it into the back of the cradle..?</TD></TR></TABLE>

he's cheap...

 

i got my car adapter for like $10 or under.. but you can do the complicated and hard way to save maybe 4 dollars, but waste a lot of time, or you can buy the adapter and plug it in in like 20 seconds..