very flexible usable product

This now has some features more (this is possibly more but also for the more than worked TS2 a / b)

software-based enhancements:
- Gespraechsdauer can be flexible configured
- Each button can even be linked to its own number
- If necessary, even with alternative numbers (if the main number should be used)
- The call duration (how long is rung) can be configured now
- Optional Gespraechsannahme after Dialtoneempfang (useful in telephone systems (TA) operation)
- Explicit by placing Dialtone (TA but must support)

hardware-based enhancements:
- 4 instead of 2 doorbells
- Next to the Tueroeffener is another relay (very flexible programmable)
to drive any low-voltage devices (bells, etc.) available.

I hope I do not forget too much innovations :-)

Overall, a great product that I even at an old Siedle
TLE 051-02 operate. This is possible because of the TS4 a / b separate entrances
for Laustsprecher and microphone exist. I had, however, for this
yet provide not officially intended mode 2 Low frequency transformers
(Adaptation and galvanic isolation).

The main advantage of TS4 a / b over competing products
is likely to be in their general applicability. There is no
Dependence on certain TA vendors. With some handicraft skills
an adaptation even to any (existing) Tuersprechstellen
possible. Instead of the usual using the supplied speaker
and microphone.

A power supply is required only when using the door opener.
Otherwise, the device is content even with the power of the a / b line.