Audio interface for VOIP phones and XBox Live

Update
An unintentional (but useful) outcome of this project is that the connector used in this project is the same as the one used on Xbox 360 headsets, so this same device could be used to inject audio, such as a soundboard, into your in-game chat.

Original post below:
 
I got asked to build another phone audio interface for a colleague who spends a lot of time on the phone and wanted a way to play back pre-recorded audio to save repeating himself.

Unfortunately the existing one I build before is for traditional POTS (plain old telephone system), but the office uses VOIP phones.

I don't have a spare VOIP phone to mess with, so had to look at other options.

The normal headset jack

The phone has a headset port, using a 2.5mm jack socket, and the headsets plug has 3 rings. Given the the headsets themselves consist of just a microphone and earpiece, it stands to reason the pinouts are mic, speaker, and ground.

I don't have the actual pinout for this particular brand of headset, but I have worked with similar ones in the past and typically the tip is the microphone, ring is speaker, and base is ground.

I don't have one of those connectors to hand, but found a stereo headset one from an old hands-free kit. That it has an additional ring connection (for the 2nd audio channel) doesn't matter, it'll effectively join up with ground anyway.

In addition to being able to inject audio into the call, we still need to be able to use the phone normally, so I've used an XBox 360 controllers headphone port to provide a passthrough for the phone headset.

The quick hand-drawn wiring diagram I used. An artist I am not.

Testing this circuit revealed a slight problem, having both the audio source and microphone connected resulted in the microphone becoming inaudibly quiet. In hindsight, this is likely due to the audio source being amplified and the mic not. A simple switch added to the circuit to allow quick switching fixed that.

Adding a simple switch at this point sorted the problem.

The finished adapter in the obligatory tic-tac box

Telephone audio interface

I work from home, and my job requires I spend a lot of time on the phone, particularly in conference calls.


I could easily go and just buy a new headset or hands free desk phone, but I already have a general purpose headset that I enjoy using, and frankly, I have accumulated a lot of headsets over the years from various phones, consoles, computers etc.

One of the items I had in my junk bin was an old wall-mounted telephone - the kind where the keypad is on the handset.

Taking the phone apart revealed three PCBs - one in the base unit of the phone, and 2 in the phone itself. One is obviously the keypad, and the other appears to be an amplifier - it was on this board that the microphone and speaker was attached.

Making the connections - the main part of the interface, is really very simply. Just cut away the microphone and speaker, and replace them with connectors.

The next step is the hang up button. Hang up buttons are press-to-break - pressing the button breaks the circuit, so as it stands connecting this to the phone line will result in your line being open.

To add extra complexity on the phone I was using the hang up button was a Double Pole Single throw switch (DPST) - this means that the switch effectively controls two circuits.

When closed, the switch connects the 4 contacts (seen de-soldered above) as follows: 1 & 2, 3 & 4

Fortunately I managed to find a 'normal' DPST switch on an old amplifier PCB in my junk bin, so wired that in place.

Also, in order to make the end product neater, I removed the coiled cable between the base and handset, and cut away the keypad - I can always use my existing phone to dial. Besides, the keypad may prove useful in a future project.

All that remained was to create a new case for it. I was able to recycle an old business card box, and 3D printed a basic front panel for the connectors.

The finished box, just connect an audio source to input, and some headphones/speaker to output, and away you go.