1) Can someone please help me what the exposed pads on the edison compute modules are for? Someone figure out one of them is for 4.5v input. Is there a way to solder usb connection via these exposed pads?
2) Is there a simple DF40C-70DS-0.4V(51) or DF40C(2.0)-70DS-0.4V(51) equivalent with pin exposed that can be hand-soldered say (2mm or so). I am trying to avoid a breakout board coz I only need the USB.
I suppose the exposed pads were made as test points during the design process. I don't think they have any use now, and I don't recommend you to solder anything on them. You could damage the module and it will void the warranty too.
Regarding your second question, there aren't other receptacles for the Edison module. The module uses a Hirose 70-pin DF40 Series header connector. You need a DF40 Series receptacle for it, and all of them have a pitch of 0.4mm. You can check additional details of the DF40 Series receptacles here: http://www.hirose.co.jp/cataloge_hp/ed_DF40_20140305.pdf http://www.hirose.co.jp/cataloge_hp/ed_DF40_20140305.pdf.
I understand the issue. Warranty aside for us, it is quite hard to solder on that DF40 Series receptacle. All we need is access to the usb d+/d-.
Any other means? Sparkfun blocks are way too expensive for this project.
Unfortunately, the only way to interface the Edison module to an expansion board is through the DF40 Series connector. I know the connector is really small and its pins are very close to each other, but with the proper tools is possible to solder it manually. Take a look at these custom boards made by other users:
Unfortunately I don't have one. If I'm not mistaken, SparkFun has a template for the Edison module footprint. You could use it to start making your own PCB: https://www.sparkfun.com/news/1591 Enginursday: A Template for Edison Blocks - News - SparkFun Electronics