Cell phone handset

I'm $%@#$%@#$% sick of shouting into a cell phone. I want, at least for the home, a nice old telephone handset I can plug into my little cell.

Something like this.

So what's involved in that? My early guess is that this guy is just sticking the elements from standard cell phone headsets into old shells. That would certainly work, since a lot of the benefit of the big handset is just getting decent acoustic coupling.

(Don't bother joining the Yahoo group, no useful content)

Hmmm... Does the mic input on your cellphone provide a DC bias? If so, a regular phone handset wired to a mini-plug might work.

Information is difficult to find so far. I think probably my next move is to buy the cheapest headset and perform an autopsy. I did find one pinout that showed some kind of bias on the mic input.

It would probably be less trouble just to take a couple of measurements. Stick a suitable mini-plug into your cellphone and take DC voltage readings between tip-sleeve and ring-sleeve. Then take your "regular" phone, open up the handset, and see what voltage appears on the earpiece when the phone is off-hook. (I used to know this information, but those brain cells have since been reallocated for other purposes). :wink:

I'm going to have to get an Ericsson adapter to get much further. Plus a cheap headset - not very ambitous today.

However, I did find some info on the web and also pried apart a 90's desk phone handset.

A big question mark, aside from "do cell phone headsets really work this way too?", is how the call-answer button is wired.

I just pasted in my notes here:

From Plantronics M170/M175 tech specs:

Mic 3.0v, <0.4mA, impedance 3.3k
Ear impedance 150R


From some random forum:
Nokia 4 pin 2.5mm:

round tip = speaker +
next ring = microphone +
next ring = speaker -
bottom ring = microphone -

Normal 2.5mm:

round tip = microphone
ring = speaker
sleeve = ground


Analog phone from Telenor, handset:
Earpiece red and green - center pair
Mic looks like standard electret, yellow and black - outside pair.
Handset pinout, seen from pin side (other side is clip side)
Yellow green red black
Yellow is +2 vdc
Speaker measures 130 ohms DC

Well, it works, but there's a need for shielding because I'm picking up a lot of RF from the phone. bzzt bzzt bzzt bzzt bzzt.... but that's the only problem.

Turns out the button just momentarily shorts out the mic.

I ended up replacing the original handset mic capsule with the capsule from the cheapo cellphone earset, and the RF problem cleared right up. Guess there's a bit of a difference internally.

Even with unshielded wire it's not bad at all, I'll use it for a day or two before deciding how badly I need shielded cable.

I like this.
Can you post some pic's?

From what I understand you just put a headset into an old phone right?

The picture wouldn't be anything special or useful - it's just a mid-90's plastic handset with a wire going to a cell phone. Anyway, the brief summary is that it's the speaker that was already in the handset, but I transplanted in the microphone from the cell-phone headset to reduce RF pickup.


I did finally use some shielded wire, and now there's no RF pickup at all. I used the wire from the cell-phone headset, soldering on short lengths of regular wire that were then crimped into an RJ handset plug. So there's a bit of heat-shrink tubing at the handset end, but it looks OK.

Thanks, for the info.
I guess this is going to be my next DIY project.

Well, my old Nokia was getting flaky, it was time to get a better deal, and my dad wanted in on a family plan...

...so now I've got a Motorola flip-phone. Which does help quite a bit with the acoustic coupling. Plus it uses readily available stereo 2.5mm plugs. I put new plugs on my Nokia earbud sets for car use, and I'm working on getting my old Plantronics big headset working. I'd gotten it working with my Nokia, but with some RF noise. With the Motorola the RF is much much worse, so I guess it's time to dig the mic capsule out of the cheapo earbud set. Maybe the Nokia did some kind of smarter buffering on the headset jack to reduce RF noise?