Telefunken RT200 User Information page 14

The larger brother of the RT200, the RT300, features a remote control input to control the tuner via the
infrared remote control receiver in the RP300 pre-amplifier. Now that we have a firmware we can extend
and modify easily, there is no reason not to add some nice features you had always been missing...
The RP300 contains a Siemens infrared receiver & decoder chip that outputs the code of the pressed button
as a 6-bit-code (all bits zero means that no button is pressed). For the 'less intelligent' devices like the
cassette deck or the record player, some logic decodes these codes into individual signal lines for the
controllable functions. The tuner in contrast directly gets the 6-bit-code and has to do the decoding itself.
The reason for this is simple: About 20 buttons of the remote control are assigned to the tuner, and you
only have 8 pins in the used DIN connectors. Of course this also saves I/O pins at the tuner's processor, and
what is more interesting: the tuner also can 'see' codes destined for other devices in the system and react on
them. For example, if you turn the system off via the remote control, the tuner can also turn itself off
automatically. And what is more interesting: The buttons on the RP300's front panel run via a virtual
remote control whose signal is merged with the IR receiver's output, the tuner also can notice when you
switch the signal source to 'Tuner' and turn itself on. Another goodie I added to display the selected signal
source on the tuner's display for a few seconds. Adding the remote control input was relatively simple: the
signal are fed into the system with an extended low-level keyboard scan routine. Whenever a higher-level
routine queries the keyboard, this routine first checks the remote control input for a non-zero code and
returns this code in case the code translates to a 'usable' button. Otherwise, the normal key matrix scan is
initiated.
Actual Implementation
Below is a photo about how I installed the board in the RT200.
There is space in abundance in the right half of the cabinet, enough to install a standard Eurocard-sized
prototype board (160x100mm). Since this was a singular project, I didn't feel the need for a real PCB (and
the circuitry underwent quite a couple of changes...). a 40-wire ribbon cable connects the board to the
socket of the old processor. I could have used one of these handy DIL connectors for the cable, but you
know, it was Saturday and all shops were closed...Due to the low clock frequency, such a long cable is not
a problem except for slight interferences during AM receival (who needs that in a Hifi tuner anyway...). All
connections, including power supply, are made via this ribbon cable. The only other connector is the
RP300 remote control input in the rear right corner.