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Resistor ?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=72753
Printed Date: May 16, 2024 at 6:23 AM


Topic: Resistor ?

Posted By: Brianas
Subject: Resistor ?
Date Posted: February 13, 2006 at 3:18 PM

what resistor would I use to get a 12volt signal down to 5-6 volt

for factory amp turn on lead-- so very low current

thanks

Josh



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Replies:

Posted By: Mad Scientists
Date Posted: February 13, 2006 at 3:24 PM

You have to know the current to be able to figure the resistor size.. if you need a 7 volt drop, and you have 0.010 amps of current, you would use a 700 ohm resistor.

Ohms Law

Voltage equals amps times resistance

7 volts equals 0.01 amps times 700 ohms.

Jim




Posted By: geepherder
Date Posted: February 13, 2006 at 7:00 PM
For a factory Ford system, use a 1.5k ohm resistor inline on the turn on lead, and call it good.

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My ex once told me I have a perfect face for radio.



Posted By: haemphyst
Date Posted: February 13, 2006 at 9:41 PM
The preferred method would be a 7905 three terminal voltage regulator. Good for 500mA without heatsink, or 1A with heatsink. Simple wiring too... no math. Input (9 to 37VDC), ground terminal, and 5V fixed output. Cheaper than an adequately powered resistor would be too.

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."



Posted By: Brianas
Date Posted: February 15, 2006 at 9:10 AM

thanks for the replys

the resistor method did not work for some reason

but I also got a 7805 5v reg. could not find the 7905

and this works excellent-- cost $1.59  took 5 min. to solder\heat shrink

it must have the middle pin grounded though--not a big deal

thanks again

Josh

JB Customs



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Posted By: haemphyst
Date Posted: February 15, 2006 at 10:13 AM
Actually, I am glad you couldn't find the 7905... That's the NEGATIVE 5v voltage regulator. Typos of this sort can be bad... The 7805 IS the number you wanted, and I am glad it all worked out for you!

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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."


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