# Google Glass 3.5mm jack with battery neck strap

I'm thinking of improving my Google Glass by DIY building a micro usb to 3.5mm headphone jack with a battery connected to a neck strap out of parts from the internet.

I've already built the neck strap with gorilla clamps and a sewn in pouch at the back to house my 2600mAh USB pocket Power pack Charger External battery pack. It's nice and slim at 95mm x 25mm and round so sits on the back of the neck comfortably.

What I do want help with is the electronics. From what I have researched Google Glass uses a Maxim integrated MAX14532E chip to switch 3 functions, USB, TTY, Audio. In audio mode the pins represent the following.

• Pin 1: +5V
• Pin 2: Right audio out
• Pin 3: Left audio out
• Pin 4: Detect
• Pin 5: GND

Also I've read that a 500kΩ resister will switch audio to stereo and 1mΩ will switch to mono.

Sooo my theory is that if I connect it all up like the following I should have a wearable addon battery pack that should double the battery life and a 3.5mm stereo jack for my beats earphones ?

• Pin 1: + from battery pack
• Pin 2: Right audio out
• Pin 3: Left audio out
• Pin 4: 470kΩ 1/4W 0.25W ±1% metal film resistor (Couldn't find 500kΩ)
• Pin 5: GND (resistor and battery)

Total cost for this if it works is about £35, £70 with some good earphones ! Just I'm in the UK and don't want to brick my glass lol I can't get another pair.

• Where did you read all the info? On the part datasheet the control is done via two pins, and it seems to me that one of them is hooked to $V_{BUS}$ through a diode, but that's just the typical application circuit, who knows what's actually in the glasses. If you consider your source trustworthy, go for it. Just find the rigt R: there's the $499k\Omega$ in the E96 series (1%), or put two $1M\Omega$ in parallel. These reisistors usually need to be precise. Commented Apr 27, 2014 at 12:47
• My information was mostly from here. stackoverflow.com/questions/19738163/… and a few other posts about people successfully making them and testing. I cannot find the other post now but another guy confirmed this info by looking at the source code in the kernel for google glass. Commented Apr 27, 2014 at 14:32
• Well wanted to check the info with some people that really knew there stuff and you have changed my mind about the resistors so was worth asking. :D Wasn't sure about charging the device while in audio mode too. Commented Apr 27, 2014 at 14:40
• Read a few things that would suggest it would. Hopefully it will. I'll keep you posted. Commented Apr 27, 2014 at 15:38

• Well it seems we agree on everything... But the $499k\Omega$ resistor should be also in the E96 series Commented Apr 27, 2014 at 12:50