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12V to 9V question

W

Web250

n00b
Joined
Jan 30, 2005
Messages
13
I recently built a sound-activated LED kit that runs on a 9V battery.

It would look frickin sweet inside my case, so my question is:

Can I hook up the 12V and ground leads from a molex connector to the negative, positive leads on the 9V battery hookup respectively, to run this? I know I'd need a resistor, I have to figure out the total ampherage of the setup first though.

How would I do this, hooking up the power, resistor, etc....?
 
i assume that the kit runs on some sort of IC... how many LED's are on the board? the value of the resistor doesnt have to be exact...

i would say somewhere between 20-40 ohms, 1/2 watt. this assumes a current draw between 75 and 200 ma. if there are a lot of LED's, you may need to drop the resistance down a little more.

the other option is a variable voltage regulator, but a resistor *should* work as well

EDIT: BTW, where did you get the sound activated led kit from? im just wondering because im trying to figure out how to build the circut on another forum... did the kit come with a schematic? if so, please PM me
 
The kit has 25 LED's. It has 2 IC's. Also there are 12 resistors, 4 capacitors, and 7 transistors.

Any guess on what type of resistor I'd need to limit the power, and how id hook it up?
 
Don't use a resistor. The load is variable, and by Ohm's Law, the voltage across the resistor will change with the load. This means that the voltage of your kit will not stay constant.

Go with an LM7809 or equivalent voltage regulator. Digi-Key and others have them with wide availability. Most voltage regulators nowadays require few or no additional components, and only have a couple of terminals, so they are very easy to hook up.
 
xonik said:
Don't use a resistor. The load is variable, and by Ohm's Law, the voltage across the resistor will change with the load. This means that the voltage of your kit will not stay constant.

Go with an LM7809 or equivalent voltage regulator. Digi-Key and others have them with wide availability. Most voltage regulators nowadays require few or no additional components, and only have a couple of terminals, so they are very easy to hook up.
Click to expand...
Damn - beat me to it :(
 
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