This topic has been discussed before by several individuals. So now it's my turn to offer a solution that I have not seen discussed yet. Please feel free to comment if my search skills are lacking.
By happenstance, I've got 2 BM5500s in my shop, sitting and waiting for a second life. The shortcomings that I can immediately spot in the design are the lack of Powerlink ports, and a dedicated AUX port. Signals for both of these features appear to be readily available utilizing a series of cables/extra equipment/internal modifications/etc, and there have been a few threads over the years by users who have prescribed various solutions. I thought I'd take a stab at it myself, and see if I can make my own companion plug-and-play "super dongle".
Looks to me like almost all the information I'd need lies within the available external ports on the BM5500. I have L&R, Power On (via the sensor, I think!), DL80, DL86, and Ground available.
TP2 & AUX : Using a tiny Arduino controller reading DL86 updates, I can monitor for source changes, and mux Tape2 and Aux inputs into the BM via a relay. That effectively creates 2 independent ports from the single TP2/AUX. TP2 will carry the DL80 signal from pin 7, and AUX will carry the DL86 channel from pin 6.
Powerlink: I've got most everything I need, but I may also need to rely on DL86 to poll for the Mute bit to trigger speaker-on, and if the Sensor hack doesn't suffice for "Power On", then I'll need to monitor DL86 for "Zone on" as well. I'm also not sure how "overload" is implemented, so there's some research required there. DL86 comes again from the TP2/AUX pin 6, and it looks like I'll snatch L&R output as well.
I've already written the code to decipher and send DL86, so much of the work is in the circuit design. Alas, I'm not a competent circuit designer, so this project may ultimately be added to the long line of incomplete projects I seem to embark on until I get distracted by something else. Hopefully an enthusiast with downtime out there can be inspired to assist me. Any takers?
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5 replies
This sounds intriguing, exciting and a really worthwhile project.
But also way beyond my level of experience or expertise 😵💫
I hope you find a suitable partner in project-crime.
Location: Kent, UK
My B&O Icons:
Beofan for many years with a penchant for 1990s audio systems.
Nice project to look into. I have e few inputs to your Powerlink thoughts
TP2/AUX pins 1 & 3 are line-level, from what I know. Those pins are directly connected to the 5500 line-out L&R pre-volume control, so the RCA outputs would be another place to hookup if need be. I'd probably prefer to just use the Din-7 plug for minimal # of connections (2, at this point: TP2/AUX, and SENSOR), unless there's a stumbling block I hadn't considered.
A cursory look at the schematic indicates that SENSOR also carries a DL86 bus, so that's another connection option. It also might make sense to have a SENSOR pass-thru on the dongle, so all function is retained. I wonder if I can just power off of this plug? There's no dedicated ground pin - only the casing - so that's something to consider.
Courtesy of some input from Madskp offline, I've considered a few more design alternatives. Instead of a specific TP2/AUX splitter, it could be made into a TP/BG/AUX-TV selector, configurable to be selectable using any of the 32 B&O sources. This would make the dongle more useful in other environments. There's a bit more management and tracking of state that has to happen, software-wise. And if we swap out the SENSOR input for a USB charging port and external power, and instead rely on DL86 for system state for Powerlink, the dongle should work in other environments. If I'm thinking about this correctly, its similar to a software-configurable MCL2AV device, tied to and controlled by outputs from the Master.
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