MIDI Transport Controller

Deconstructing the Rotary Encoder

HR-VP720U Remote

The VCR remote control, from a JVC HR-VP720U VCR, featured a small jog/shuttle dial at the base of the remote control unit. I removed a single screw from the battery case area and pried the plastic case apart. At the lower end of the printed circuit board, the jog/shuttle control was soldered in place with 7 leads. A soldering iron and some solder braid made quick work of extracting the control.

The Jog Wheel

I presumed that the the jog wheel was a rotary encoder and at least two of the 7 pins were used for it. By placing an ohm meter between consecutive pins and rotating the dial I was able to see the meter react, dropping to 0 ohms and back to infinty again quickly. This seemed to confirm my suspician regarding the rotary encoder, although it was not completely clear which of the 3 pins I had discovered served which function. This became clear later, on the breadboard.

The Shuttle Dial

Next I had to determine how the remaining 4 pins related to the shuttle dial. I fully expected the shuttle dial to be represented by Gray code. If a common ground was shared with the jog dial that would leave 4 pins to represent a 4-bit Gray code. Again, the ohm meter was employed to detect contact closures between the remaining 4 pins.

It soon became apparent that none of the pins from the jog wheel encoder were shared with the shuttle dial pins. Still, I reasoned, a 3-bit Gray code would be sufficient for a shuttle wheel. I needed only to discover which pin of the remaining 4 was common.

By placing the ohm meter leads accross each combination of the 4 unknown leads I found only one pin that was shorted with each of the other 3 when rotating the shuttle ring. This, it seemed obvious, was the shuttle common lead.

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