Make your own USB to 2.5mm adapter

In my review of the A218 MP3 watch, I discussed the primary problem with the watch. It has a 2.5mm port which serves as the data port and the headphone port.

If you know anything about modern audio electronics, you know that most of them utilize a 3.5mm port. Almost any headphones you have ever seen have a 3.5mm jack. The same goes for products such as the 2nd Generation iPod Shuffle which utilizes a multi-function audio port. It can be used as an audio port or as a data transfer port. But, all of these products will still utilize a 3.5mm port.

The A218 MP3 watch is a little different. Because it uses a 2.5mm port, you are limited on the types of cables and adapters that you can use.

Of course, the watch does come with a USB cable and headphones which will fit this 2.5mm port. However, the primary problem with this is the fact that the USB cable which comes with the watch is 12 inches long. In order to use this watch as a flash drive, you have to carry this long cable around with you everywhere. The purpose of the watch is portability. The 12 inch cable completely defeats this purpose.

So, I attempted to find a solution.

I found a USB adapter for the 2nd Generation iPod Shuffle. It is a very small adapter with a male USB on one end and a 3.5mm jack on the other. In order for this to fit the watch, the 3.5mm jack had to be reduced to a 2.5mm jack. These adapters are very easy to find. So, I ordered the iPod Shuffle adapter from eBay and picked up the 3.5mm/2.5mm adapter at Radio Shack. Once the iPod Shuffle adapter arrived in the mail, I connected the pieces together, plugged them into my MP3 watch, and waited for the magic. Much to my disappointment, nothing happened.

Apparently, the USB data signal will not transmit through a 3.5mm/2.5mm adapter. The 2.5mm jack has to be directly wired to the USB plug.

So, I tried to find an adapter that made a direct connection from a male USB to a male 2.5mm jack. I searched the Internet thoroughly. I even emailed manufacturers. No success. There isn’t an adapter like this anywhere on the market…none that I could find anyway.

So, what do we do when we can’t find what we need? We make it.

I started gathering the necessary materials, and studying up on the proper procedures. I found an old USB cable and a 2.5mm jack. But, during my research, I discovered a crucial aspect of the 2.5mm jack. The jack has to be a 4 pin jack. This means it has 4 connection points on it. You will know if it is a 4 pin jack because the tip will have 3 black rings on it. Most only have 2. Some even have 1.

So, I had to find a 2.5mm, 4 pin jack. Luckily, the MP3 watch came with an extra USB cable. So, I robbed the 2.5mm jack from that.

I had all of my parts:

Now comes the hard part…putting it together.

First, I had to figure out which cable connects to which. The USB plug has 4 cables…Red, Green, Black, and White. During my research, I discovered this page which is a guide on making a similar adapter for the iPod shuffle. Though the adapter on this page uses a 3.5mm jack, the principle is essentially the same.

There was a small problem, however. The diagram on this page told me which wire to put on which connection, but on the wrong end. It points to the tip of the 2.5mm jack which plugs into the watch. Obviously, you can’t solder to that end. So, I had to use an ohmmeter to figure out which connection corresponded to which soldering point. To save anyone else the hassle, I have revised the diagram to reflect this.

Once I had this diagram, I started the soldering process. It’s not easy. The parts are so small, and the plastic on the 2.5mm jack has a tendency to melt from the heat. But, I eventually got all the wires soldered on to the 2.5mm jack.

I plugged it in to the watch, plugged the USB cable into my Computer, and witnessed the most amazing thing. It actually worked!

The hard part was over with. After that, I made a basic casing for the adapter which consisted of the original USB casing and a little epoxy. I then connected a key ring to it and…Voila. I had a USB/2.5mm adapter that I could carry around with me anywhere.

The work gets a little tricky, but it’s really worth the effort.


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