Hello everyone.

I have an old mp3 player (Cowon S9) but the power button broke and I eventually bought a replacement. Now I want to use this to stream music in my car. I can solder on a new button and use it normally but I want it to turn on/off automatically with my car.

Essentially I dont want to use the inbuilt battery power now. I want my player to turn on when it is plugged in (which it does anyways) and turn off when I disconnect it (which it doesnt...it starts using the battery).

I have been thinking of ways to do this but I am drawing a blank. Some on the ideas I have so far:

1. Add a reed relay near the battery which disconnects as soon as the usb power is disconnected. This should work but the problem is the only points from where I can harness the power for the relay coil are impossible to solder on. The other points also get power from the battery and therefore useless for me.

2. Remove the battery all together and replace it with a capacitor of some sort. This in my head should behave like a battery but only that as soon as power is disconnected the capacitor will discharge quickly and turn off the mp3 player.

Do you think the second idea would work? If it will what kind of capacitor should I use? A 4.7k uF electrolytic will work? Any other ideas that you guys have about this?

Thanks everyone for reading!

 

I think the capacitor idea might work. Use as large a cap as fits in.

 

I think the capacitor idea might work. Use as large a cap as fits in.

Why do I need a large cap? I was thinking I want it to charge and discharge as quickly as possible. I was thinking a 4.7k uF cap and a 50ohm resistor instead of the battery.

 

You already have one thread for this, in the "projects" forum.

 

You already have one thread for this, in the "projects" forum.

I know. I apologize about that. I think I will delete that thread.

Edit: Seems I cant do it on my own. Apologies again for multiple threads!

 

I think you meant this was for your houseboat, right?

 

I think you meant this was for your houseboat, right?

Nope no houseboat. For my car. I am planning on installing an inline FM transmitter with bluetooth streaming and want to use my old mp3 player to stream the music. I dont want to have to dock my phone everytime I get into the car.

 

Take the battery out. That way it only gets power from external source.

 

Take the battery out. That way it only gets power from external source.

Doesnt work. First thing I tried.

 

So I finally picked up a multimeter from my friend to measure a few voltages to see whats happening.

I am taking the readings at the point where the battery is soldered on. Here is what I found:

Battery Connected: ~3.9V (which makes sense because I think its a 3.9V LiPo Battery)

Battery Connected + USB power: ~4.10V and keeps increasing as the battery charges. I will update with fully charged voltage when I get it.

Now for the ones I dont quite understand.

Battery Removed + USB power: ~2.4V

And then after a while the player turns on showing battery is fully charged even though battery is not connected. I am guessing some capacitor is charging. Now the voltage drops somewhat.

Battery Removed + USB power (showing battery full): 2.074V

At this point the screen turns on and I can use the player but the screen is really dim. On connecting the battery it comes back to full brightness.

Now I am absolutely confused as to what is happening. Can anyone explain this?

I can post pictures if that will help.

 

So looking at the voltages I tried something which seemed to work. I figured I needed to supplement the voltage from the USB connected a bit to bring the screen up to full brightness. But I later realized that it was the wrong reasoning as I was connecting the battery in parallel with USB power. So the current gets supplemented. Maybe its just that the 500mA of current from a USB port is not enough to run the mp3 player?

Instead of the rechargeable battery I connected a 3V non rechargeable battery (a 1.5V button cell and one 1.5V AA cell...what I had available at 3:30am!). It seems to work as intended.

On connecting the usb connector now it turns on and after a few second shows that the battery if fully charged. But, now when I disconnect it turns of immediately. Seems 3V by itself is not sufficient to run the mp3 player.

Now I think adding the battery there should work out. I am just not sure if adding a non-rechargeable battery is a good idea. I think I can go with a 3V rechargeable cell instead (one of those CMOS batteries?).

I am going to take some more readings tomorrow to see how the voltages are behaving. I will also try and get some current readings. Because I dont have alligator clips it needs more hands than I have!

So what do you guys think?

 

Nope no houseboat. For my car. I am planning on installing an inline FM transmitter with bluetooth streaming and want to use my old mp3 player to stream the music. I dont want to have to dock my phone everytime I get into the car.

Gopher was giving you a hint. Read theTerms of Service and you will see that discussion of automotive modifications is prohibited on AAC. As it is your thread will stand as long as you are not modifying the existing wiring of the vehicle.