PART 3 - The control bus - DIY Infrared receiver for Pioneer Tapedecks

If you haven't read Part 2 - start here!

The Control Bus

Like a real bus bringing passengers from one station to the next and so forth, the control bus from Pioneer, called SR (System Remote), is bringing IR data (binaries) from  the Receiver or Amplifier to the tapedeck, if the binary data wasn't meant for the tapedeck, you can connect that to the next unit and that to next again. Every unit is listening for signals.

So you can daisy chain the units, Amp to Tapedeck, Tapedeck to CD player, CD Player to Tuner, etc. etc.

I found Adrian Kingstons great website, which in detail describes the Pioneer SR format.

http://www.adrian-kingston.com/IRFormatPioneer.htm

From his website i learned the following about the control bus:

"This is simply a TTL +5V rail supplied by the receiving end (CONTROL IN). The sending end (CONTROL OUT) pulls this rail down to 0V (GND) with pulses that are the same as the NEC protocol described above except that the pulses are unmodulated, that is there is no 40kHz carrier inside each pulse, its just a solid period of 0V."

With the important note:

"Note that the tip pin of the CONTROL jack plug is the SR bus pin and the ground connection between the units needs to be made with an audio ground from the LINE IN/OUT connectors."

Lets boil that down to the following.

• Must buy 40kHz IR Receiver.
• I need +5 Volt and a common ground.
• The output of the IR receiver must be +5 Volt.
• Any signal coming out of the IR receiver must pull the +5 Volt down to 0V.
• the CONTROL IN supplies +5 Volt ?? - really?

I found this TSOP31240 IR Receiver Module running a 40kHz in a range from +3V to +6V.

It's a good ideas to protect the IR Receiver against EOS (Electrical Over-stress) and in general to stabilize the Receiver with the following components. Sometimes IR Receiver are sold on a mini-board with these components already mounted and ready for user with an Arduino or other micro-controllers.

So this is what i came up with, i measured if ground comes out of the CONTROL OUT connector. And just like Adrian wrote on his website, ground is not connected at all.

Me, measuring ground to ground - no result.

I then measured if the IN or OUT provides +5V. Yeah, well OUT does provide +5V, but it's the data line which is always high +5V. To use the data line as power provider for the new IR Receiver is not a good idea. (trust me i tried)

So i am stuck with using an external power supply for my design.

Components line-up to test with the breadboard:

The usual suspects...

From left to right:

• The IR receiver TSOP31240 (40kHz) Pins from left to right: 1. Ground, Vcc and Out
• Electrolytic capacitor 10V 10µF 
• Ceramic capacitor 0.1µF
• Resistor 10k Ω (long legs)
• Resistor 100 Ω (short legs)

(See also the Schematic Diagram above)

This is how i hooked the components up on the breadboard.

Breadboard with components seen from behind.

Please note that the electrolytic cap minus pin must go to ground. the black cable going off to the right is Out. No signal from remote and it is high (+5V), any signal should pull it to Ground.

As a power supply for this test i used an Arduino clone.

Mini-scope with breadboard.

I plugged the Mini-scope (5V per division) on Ground and Out, then pressed Tapedeck Play on the Logitech Remote control.

YES - ITS ALIVE!!

In Trigger mode you can see the Play Button IR codes as they are pulled down from +5V to Ground.

Lets plug it in the Pioneer CT-S820S CONTROL IN port.

I only had a stereo cinch to mini-jack cable, that's fine. Left channel (white) is the data line. For the real setup i will use a mono trigger cable as they are called.

Note the dodgy ground wire to in the upper left, clipped to one of the chassis screws. The Uno's role is power supply.

Roll video:

Sorry about the dishwasher noise in the background, meh! Thou shall have clean plates!

I am really surprised that it just worked like that. Really great news.

Next steps: 

• Get some nice cables.
• Solder them on board.
• Throw it in a nice package.

I found this package from 1998, this will do fine. Old serial remote receiver box.

Go to Part 4.