Samsung WEP470

[bsbowens]

Jeff pointed out that this Bluetooth headset was available on Woot a week ago for just $3 (after rebate), so I snapped one up as a candidate for the handset hack. I've now cracked it open (the silver-gray plastic back is held on with seven small clips, and can be pried off) and extracted the circuit board, which I've scanned here for your viewing pleasure. Because the forum limits picture size, I've put the two scans on Flickr instead:

http://www.flickr.com/photos/46411586@N03/4263517697/
http://www.flickr.com/photos/46411586@N03/4263517875/

I think that the only potential difficulty is the call pick-up/hang-up button, which is the membrane switch visible as a gold circle just above the letter D near the top of the board. I don't know what they look like internally, but suspect that it may be possible to peel off the top layer and get a couple of wires soldered to the internal contacts. I'll try to find something similar on a scrap board and do some dissection first.

[mightyohm]

Bill,
I increased the image size limitations on the forum (sorry about that).

Here are the images you linked to (click for full size):

[mightyohm]

Ok, about that membrane switch!

There are a couple ways you can bypass it and use an external switch.

One way would be to remove the switch and solder wires to the pads left behind. This is challenging with a soldering iron but not doable with a hot air rework station. Unfortunately, not everyone has a hot air rework station handy, so an alternative would be to solder tiny wires to the leads of the switch OR any other pads on the PCB that are connected to the leads! A DMM with a continuity beeper can be really helpful here. First figure out how the switch works, ie. which leads get shorted to which other leads when it is pushed. Then start poking around and looking for other pads on the board that are connected to those same switch leads, but are more accessible (larger pads or in a more spread out area).

Frequently one side of the switch will be connected to the positive supply rail (1.8, 3.3, or 5V) or ground, both of which are usually pretty easy to find a good spot to solder to on the board (such as the test points on the backside).

Peeling off the top of the switch and soldering wires is an interesting idea too. It could work. Maybe if you cut one side of the switch and flipped the top layer up, you'd have a nice big thing to solder to. Hmmm...

Overall I'd say that headset looks very hackable.

One question - what is the orange thing hanging off one side? Are those the volume buttons?

Also, do you mind if I repost your photos on the blog?

[bsbowens]

No hot air station here. I've taken a look at the Aoyue but haven't sprung for it yet. I do have some nice fine tips for my Antex iron though, and I've done some hand assembly and repair of SMT boards. And what the heck, this headset only cost me $3 so I don't have much to lose! I'll do some poking around with a meter and see what I can find out about the switch before going to the step of peeling it apart.

The orange thing is the volume up/down control, two more membrane switches. It's just tacked to the edge of the board and should come off easily.

Please feel free to use the photos - I noticed that Flickr had a button to indicate which kind of CC license they should have but I didn't pick one since I wasn't sure which one signified "do whatever you want". I was going to take some disassembly pictures but my digital camera doesn't do macro very well. I'll try to get some more scans of the board after I get the jumpers connected to it, and some decent pictures of the installation process. . .

[mightyohm]

Sounds good! Please document your modifications and share them here.

I think the least restrictive CC license is the "Attribution Creative Commons" license, which is what I have been using.

Also, consider adding your photos to the Flickr PCB Photo Pool!
http://www.flickr.com/groups/pcb/

[bsbowens]

Stole a few minutes to poke at the board last night and made minor progress with the call pick-up switch. One contact is ground, the other sits at about 1.5v when the device is turned on. But since I couldn't find a pin connected to that side of the switch, I decided to dissect it. The yellow plastic film is just adhesive tape, and the metal disk is held down by it; lifting one corner with a knife allows both to be peeled off with tweezers. The contacts inside look like they ought to be solderable, though I may use only the one side and just tack a wire to one of the ground pins on the charging jack.

I may have to look elsewhere for a handset, the donor phone I'd had in mind is a very old one and the interior space in the handset is very tight. I'm not sure the board will slip inside. Might have to hit some thrift stores and see what I can dig up. . .

[mightyohm]

Good to hear you are making progress!

The handset I used is pretty roomy inside. I think it's a 70s/80s ITT desk phone handset. I've seen a lot of them around so it should be pretty easy to find one, but if you're looking for something exotic then please don't let me stop you.

What are the overall dimensions of the WEP470 PCB? I wonder if it's larger that the Mot headset I tore apart?

[bsbowens]

The PCB is .55" x 1.52" and about .3" thick sandwiched with the battery. I think that's a bit narrower than yours.

I have another, more recent handset that would probably work better, but I actually *use* that phone! The limitation with the handset I want to use is simply that the plastic is much heavier than a 'modern' one, so although the outside dimensions are the same, the cavity inside is quite a bit smaller. Have to see whether I can wedge it in. I might end up sacrificing the microphone element and using the electret instead, to get a bit more room.

BTW, I watched Kip's video today and saw that he had a headset with a disposable battery. It reminded me that Jabra makes a headset, the BT2040, that needs a single AAAA cell and sells for almost nothing; around $10 and sometimes a lot less. I believe Woot was selling them for $3 at one point, without a rebate. That might be a good candidate for the conversion.

[mightyohm]

I wasn't aware of the $10 headsets, thanks for sharing. That could be a good option for folks that missed the woot offer.

[bsbowens]

Interim updates, prompted by your tweet this evening. . .

I was able to tack wires onto contacts inside the call pick-up switch, and I also peeled off the power switch and attached somewhat heavier wires to it. But because they're two separate switches (unlike the headset used for the original version), I'll need both a pushbutton and a toggle switch. I'm trying to decide where to install them in a way that won't interfere with using the handset.

The best bet may be to have the power switch hidden inside; I considered just leaving the original one in place, but it was hard to switch with the board slipped inside the handle. That would require opening the microphone compartment to turn the handset on and off, but might be an acceptable compromise. Then I'd only need a charging jack and a single pushbutton on the outside.

I spent a while looking at the status LED before concluding that it is just too small to attach any leads to. My initial hope of being able to position the circuit board so that the LED would be visible through a hole in the handset has proven impossible, so this version will be unlit.

Overall, I'd give the WEP470 a mediocre grade for hackability. It would be a lot nicer to have a single momentary switch for power and call pick-up; it'd also be better if the LED could be removed and remoted. Now I'm wondering about that cheap Jabra. . .