Hi all,
This is a continuation of FT-817 Phone Audio interface part 2.
It has been a while since I have posted on this topic, and the principle reason for that is that I was patiently, and then not so patiently waiting for boards that I had ordered. They arrived while I was away on a series of SOTA activations, but I have populated one of these boards and tested. Apart from getting one of the cables wrong – which I needed to fix, everything works quite well. The markings of the rectifier diodes are wrong, but I already knew that upon ordering as that is a bug in the device files in my design software.
There is quite a lot of latitude with the potentiometer settings, both audio in to the phone and audio out. I ended up using a volume level about 2/3rds on the phone. There is going to need to be individual adjustment of these, as it is a function of the phone used, the digital mic setting on the radio and also the need to ensure that the signal is not being splattered. If you do not have access to two radios with one having an existing audio interface – eg a Signalink for testing, then you will require some on air reports to ensure that your audio is at a good level without causing splatter.
Here is a pic of both an unpopulated board and a populated board. For an Samsung Galaxy S2, I used a 12K resistor for R10. Apple devices might need a lower value, around 4.7K to raise the current that the interface draws. It seems like around 600uA is the threshold for Apple devices, but the Galaxy S2 is happy around 300uA.
Populating the board is quite straightforward. Although most components are surface mount, they are either 1206 or 0805 size, and I did not even need to use a magnifying glass. I recommend using a temperature controlled iron with a fine tip.
I have a few spare boards, and can make these available for $12, or $25 with the parts, either $A or $US plus postage. Send me an email at vk3wam@gmail.com if you are interested.
It should be possible to adapt these boards for use with other radios as the connectors at each end are straight inline. On the phone side, most modern devices have ground on pin 3 and mic on pin 4, but many older non-Apple devices are the other way around, ground on pin 4, mic on pin 3. If you have such a device, then you’ll need to wire it that way. On the radio side, RX audio (phone in) TX audio, GND and a PTT grounded to TX signals are required and most radios should support these. The Yaesu radios provide a constant audio input on their data port, but some radios (I believe the Elecraft KX3 falls into this category) will change the output audio based on the AF gain (volume) setting.
73 de Wayne VK3WAM
waynemerry 
In testing good audio levels, I have found that best operation is to turn the phone right up to maximum audio level. This makes for more reliable PTT activation. The audio level is quite strong, so the R8 potentiometer needs to be turned down – right down – to about 1K between signal and ground and 9K extra resistance. The potentiometers I am using go over full range in about 20 turns, so it is still not overly sensitive. I used DroidPSK to TX, and slowly turned down R8 until the ALC meter showed nothing.
If I had the potentiometer up the other end – that is about 10K between signal and ground and no extra resistance between source and output, what I found what that I would need the phone on about 1/3rd volume to have no ALC, but PTT triggering was quite unreliable at these levels. Also, by just changing the volume level on the phone up one level, I would go from no ALC on the FT-817 meter to full ALC, plus splatter extra. Operation would be easiest with having the phone on max volume with levels set for no ALC – there would be less chance of mistakes.