ZRTP Hardphone

Made a new box, put everything inside and wired it. 

So cool, I thought.

Then, plugged it to the power and find out that you can listen the radio on the ring speaker. And some other noises too.

After reading the Ganssle article about analog noise made a few tests to isolate the source. I thought that the problem comes from the mains power supply and the nearby powerful AM stations. Can hear the radio even with the input cable disconnected.

Also there is no protective earthing on my house (or neighborhood).

Installed the amp inside a metal box and moved the power supply further, but the noise is still there.

Just discovered that twinkle does not support TLS for the SIP auth.

Fortunately, there is another project called SFLphone with TLS and ZRTP support :)

So the plan now is to use the SFLphone core. I'll have to write the software to interact between the UI and the core.

A cardboard box

is free and easy to work with.

The box is turned the inside out, so it is possible to write things on it.

All the human interfaces are in place now. That was easy and fun to mess with. 

Hook made with cork stopper and aluminum foil. All glued with cyanoacrylate.

Got this old phone for 3 €. Thinking about reusing the handset, keyboard and case.

First thing is make a call with ZRTP to check if the raspberry pi is powerful enough.

After installing and configuring Debian and twinkle, I am very pleased to announce that it works flawlessly!

Next step: human interfaces.