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car audio at home no keeping presets problem

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ouchthatcurrent

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I built a home sound system using a computer power supply and car audio head unit but I lose the presets every time I switch off. There is a yellow wire from the audio unit for memory. Can I connect this to the positive of a 9 volt battery whilst the unit is being powered by 12 volt? Maybe place a 1 amp diode between the positive terminal of 9 volt to stop the 12 volt from trying to charge the 9 volt? Would this work, ie keep the memory presets when the 12 volt is switched off? Sorry, don't know much about electronics.
 
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tpetar said:
Yes you can. This will work if 9V is enough for this job. Dont forget to put diode.
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That's good :smile: I'll try that. I can get a low voltage warning kit so I'll connect that too. Thanks.

(Just for interest, what would happen if I forgot about the diode?)
 
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Update: this works! But I will see how long the battery lasts for before saying the problem is solved.
 

ouchthatcurrent said:
Update: this works! But I will see how long the battery lasts for before saying the problem is solved.
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I don't know what's typical for a car stereo, but you could try to measure the current in the memory line to get an idea of how long the battery will last. The current could be so low that you can't really measure it or it could be in the milliamp range.

If you left out the diode, your initial statement could come true. The 12V could try to charge the 9V battery with very bad results.

Ed
 

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