BL3500 and the MCL/PL connector

[swo]

Beolab 3500 Mk II
Tested with SW 3.33

When the Beolab 3500 Mk II is in PL mode, it behaves like a normal BL speaker (BL6000, BL8000): no IR reception, no SelectSource, and also no Vol+/Vol-. A speaker like that having its own display doesn’t really make sense in the first place.

⚠️ Big warning: PL-level audio signals are much lower than a typical Line In / audio jack level. Since the Beolab 3500 Mk II’s volume can’t be controlled over PL (see above), feeding it a normal Line-In-level signal directly risks destroying it. Attenuate the input first — a voltage divider, or a level control on the source device — before connecting it.

The basic idea
Without display
Simple, two things needed — tie PL4 to +5V, and send 0011000111100111111100000000100 on PL6 / PL7.

With display
It gets more complicated — two additional requirements:

After the frame’s normal Stop (t4), one more t1 pulse (3.125ms).
Mute (MK2_MUTE_PIN, GPIO26 in main.cpp) must only go HIGH after that init sequence (0011000111100111111100000000100) has finished sending — it has to stay LOW for the whole duration of the sequence.

• This reply was modified 1 hour, 8 minutes ago by swo.

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