With Apple's lightning cable, and USB 3.0, reversible cables are taking off, and I personally think this is very convenient. But we have had better than reversible for a long time, in the form of the headphone jack, which can be inserted in any direction, not just 2 directions. Why isn't a headphone jack shaped connector used for data more often? All I ever see that shape used for is audio and power supplies (I've seen it used once for data, in the iPod shuffle, but thats it).
Electronic – Why aren’t headphone jack shaped plugs used for data
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Related Solutions
Based on the manufacturer's youtube video for the app compatible with the cable:
This is a video guide for SmartLog(Blood Glucose Management Software) App represensted by i-SENS. SmartLog App is a smart phone application which helps patients with Diabetes to monitor their health conveniently anywhere anytime. This app works with CareSens N NFC meter. CareSens N and CareSens N POP meters can also be used when using FTDI cable.
A FTDI cable typically refers to a USB to RS232 (TTL level Serial) IC FT232 (or other generations of the FT232 chip) created by FTDI. They also make other USB bridge ICs with similar functions.
Connecting a USB cable straight through to a 2.5mm plug will most likely cause a problem. as you have already seen.
If it's a simple straight through connector, it will have Ground, TX and RX. FTDI's official 3.5MM cable uses Tx {To device from PC}, Rx {From Device to PC}, Gnd (Tip, Ring, Sleeve, respectfully). With your multimeter, you can confirm the 2.5mm pinout by doing a continuity test between each section of the adaptor and your 3.5mm cable wires, then confirm the signal by checking for voltage between the three wires. The voltage it runs at is a concern because using a 5v signal on a 3.3V port might be bad.
Of course it could be more complex. TI calculators used a 2.5mm port for their Graphlink cables. It was able to connect to a serial port, but required 6 pins, resistors and diodes between.
If you had a cable to hack up, or even a meter to hack up, it would be easier. They occasionally pretty much aways give the device away for free, check with your doctor or the manufacturer's local sales rep.
Update: Based on the two links below, the pinout is more likely to be Tx from Device to PC, Rx From Pc to Device, Ground (Tip, Ring, Sleeve). Like a defacto standard amongst Diabetes Meter manufacturers. You need the USB to serial IC for the OTG cable, but you could use a serial port for the PC instead (I am not liable if you fry your meter).
http://pinoutsguide.com/Electronics/bayer_contour_pinout.shtml
http://www.diabetesforums.com/forum/topic/65566-abbott-freestyle-freedom-lite-data-cable-how-to-some-other-info/
Reading data from a glucose meter
There's only so many ways you can make a connector that rotates. The connections have to be on a single axis in order for the rotation to work, so that rules out everything that isn't, at the core of it, a jack of some form.
It's possible to get multi-pin barrel jacks (some laptops use them) where you have two concentric rings, and the inside and outside of each ring is a different connection. Expensive though, and hard to find.
So it's really your typical jack plug. Don't worry, they have been used for decades for non-headphone devices.
Telephones used to use a variation on them many years ago:
But then of course, there's multiple sizes. Modern jacks come in 3 basic sizes: 1/4" (the large headphone / audio jacks), 3.5mm (your normal headphone jack) and the smaller 2.5mm ones. These latter are more often used for control and data as opposed to audio - they were often used with microphones to start and stop a tape recorder - and many modern devices use them as a computer interface connector for UART or USB communications.
So I'd say use a 4-pole 2.5mm jack and you shouldn't go far wrong.
Best Answer
Digital signals are highly susceptible to the noise generated by rotating the plug.
For audio, these noises (cracks) are rarely audible unless they last longer than 50us (simply because of the fact that we're unable to hear frequencies over 20kHz). So, the cracks becomes audible only when the surface of the connector has deteriorated enough that the period of lack of connection is substantially longer.
As a rule of thumb, any connector where there are moving parts while the connection is established, is a terrible idea for high frequency digital data. It might be acceptable for low frequency digital data, as well as power supplies.
Finally, most digital standards require quick detection of the disconnect - even though the above issue could be worked around with proper ECC (Error Correcting Codes), USB assumes that any loss of connectivity for over 2ms is considered a disconnect. (USB 3.0 SS is even more strict).