how do I connect the DC-AUX in and the battery to the 7805?

mindstein · Post by **mindstein** » Sat Sep 11, 2004 9:22 pm

I am trying to connect the DC-AUX in and the Battery to my portable and don't know how to keep the power from the DC-AUX in blowing my battery.

If I just wire the positive from the battery and the positive from the DC-AUX in to the 7805 HI IN and use a common ground wont the power from the DC-AUX in flow to the battery and blow it out when conected. How do I prevent this? Do I use some sort of pull down resistor and short the battery when the DC-AUX is pluged in and of so how do I do that?

The charge plug for the battery wont matter because the portable will be off and the DC-AUX plug will not be in use when charging so the current will flow from the charger to the battery.

But how do I wire the DC-AUX plug and the battery to the 7805 and have the power from the DC-AUX not flowing into the battery?

I know this a feature that many of you and Ben use can any one help?

Post by **gannon** » Sat Sep 11, 2004 9:28 pm

You need to get a dc jack that automatically switches, or you need to use a spdt switch to manually switch between the batteries and dc input.

mindstein · Post by **mindstein** » Sat Sep 11, 2004 9:59 pm

thanks Gannon. I will try to find one that does that.

I have also considered just bypassing the 7805 from the DC-AUX input, and just using a wall wart that is rated corectlly. I happen to have 3 old Zip drive wall warts that provide 5v at 1amp. and this would not need the 7805 at all and the connections would be separate. only the battery would use the 7805.

But this means that I always have to have that Zip wall wart.
And If anyone plugs in a larger power supply it will fry.

If I use the 7805 and the switching DC-AUX in plug I could use any wall wart around with the enough amps. And it would be a saftey against frying.

What do you think about this? which way would you go.

Post by **SpongeBuell** » Sun Sep 12, 2004 6:43 am

I wouldn't bypass the 7805. You really risk frying your board. In addition, the color tuning potentiometer needs more than 5 volts (at least 7.5, I believe) and if you just give it 5 you probably won't get any color.

Guest · Post by **Guest** » Sun Sep 12, 2004 5:22 pm

Hi SpongeBuell,
you know I had forgotten that the color regulating pot needed more than 5v.
Thanks for the heads up. I don't know what I was thinking.

I also didn't feel comfortable bypassing the 7805.

My portable already has to may switches. So I will have to locate a DC-AUX plug that will do the switching for me.

thanks again.