Pioneer SX-950 Stereo Gets a Motorized Volume Knob Remote Control Using HDMI CEC

Stereo receivers from the '70s, '80s, and '90s were engineering marvels that still appeal to audiophiles young and old. There’s a certain amount of magic that emanates from speakers when the front panel face comes to life with all of their dials, buttons, and switches illuminated by an incandescent glow. When Thomas Sowell’s '90s-era stereo receiver stopped working back in 2017, he managed to get his hands on a Pioneer SX-950 from Craigslist. Pioneer made great receivers back then, solid construction with a satisfying weighted that provides momentum to travel from one end of the radio spectrum to the other.

There was only one slight problem — there was no remote control for this model, and like most of us, Sowell didn’t want to manually adjust the volume every time he wanted to listen to movies and TV shows, so he designed a remote that would keep him off his feet. IR and RF solutions went out the door for this project, in favor of HDMI CEC (Consumer Electronics Control), which was more comfortable for Sowell to implement, considering he was going with a motorized potentiometer for the volume knob.

Sowell originally planned to mount the entire motorized potentiometer assembly outside of the case as a series of capacitors made that space limited. The motor was just too large to fit in the cramped area, but Sowell opted to solve the problem by flipping the capacitors to the underside of the PCB and bending them to the sides. As mentioned earlier, Sowell chose the HDMI CEC route for controlling the volume, which he was able to accomplish using an ATtiny4313 microcontroller and a half-H driver.

Of course, the CEC protocol utilized by his TV was sensitive to his timings, so Sowell threw in an external crystal to the mix so that it would recognize the microcontroller. After adding a few failsafes, and a nice enclosure, his remote was good to go. Those interested can visit Sowell's blog for a complete walkthrough of his build.