Monday, November 12, 2007

Batteries and MP3 Players

I like to play with Audio, especially cleaning up and creating MP3 songs. The device I use is commonly a Zen player. The sound quality of Zen players is really very good and I prefer to use a Zen rather that an IPod because I dislike the proprietary nature of these devices.

There is however, one major downside to the Zen players that utilize a rechargeable lithium battery. These units require a USB power source with the data lines active, meaning that if you try to charge them with say a USB car charger, the USB connector only has the power lines connected and no data lines. This means that most people will have to buy an expensive charger from Creative, who make the Zen, or use the USB port on their computer. The latter is a very expensive method of charging the Zen player if it requires many hours.

There is however, a very simple and inexpensive workaround. I’ve found if you buy a USB car adapter/charger and a low cost 4-port hub (no power source and even USB 1.0) you can connect the hub to the car charger and then the Zen player to the hub, and it will usually charge the device. I have come across a few hubs that won’t work, so buy locally so you can return the hub for something else. I bought my car chargers from a local computer swap meet and was given some sample hubs for free (maybe because they were USB 1.0).

I’ve gone a stage further and this may also interest MP3 player users who have the type of player that doubles as a memory stick and has the USB connector built-in, which is revealed by removing a cap. These units generally also use a AAA battery and replacing these batteries all the time is frustrating and possibly expensive, as well as polluting the environment.

Using a spare USB car adapter/charger, I took the unit apart and removed the PCB/connector. I also unsoldered and removed the 12-volt spring connections used to make contact in the cigar lighter socket. Using a 4" x 2" x 1.5" plastic box, I cut out slots for the USB connector on the car charger board, and a slide switch for power. I also placed two Li-Ion 18500 Cylindrical Cells (3.7V 2200mAh, approx. 18mm Dia. x 65mm long) in series inside the box. I leave it up to your own creative imagination as to the method of securing these parts (I mainly used hot glue, heavy copper wire and tight fits). I also added a 3.1 mm power socket to charge the 18500 Li-Ion Cells. These Lithium-Ion cells will actually charge up to 4.2 volts, but I generally don’t like going over 4.0 to 4.1 volts so as to extend their life. Two of these cells in series yields just over 8 volts which is enough to still produce the 5 volts at the USB connector, and the cells won’t discharge to below their critical 2.5 volts.

This newly created USB adapter/charger can now serve a number of purposes:

  1. As a Zen charger by using the aforementioned USB hub.
  2. Plugging in a memory-stick type MP3 player without the AAA battery and as soon as power is applied it works just like a player because there are no data lines. This is great for my garage where I leave it on for endless hours.
  3. As a charging device for any other USB charging device such as a cell phone.

The only remaining challenge is a reliable method for charging the two Li-Ion 18500 Cylindrical Cells. I was fortunate to have an 8.4 volt Li-Ion charger, made by Canon for a video camera, but I also have a number of solar panels that will do the job. Without a specialized charger, it is very important not to let the batteries overcharge. A low cost method is to build an electronic timer and a constant current generator—which can even be a low voltage incandescent bulb that can handle 1 or 2 amps placed in series with the Li-Ion batteries and a low voltage DC source.

I've just bought a refurbished Creative MuVo 2GByte MP3 player (for $29 on the Creative site) and this also works with the newly built Li-Ion USB adapter/charger.