- Published: Thursday, 19 July 2012
- Written by Jon Chandler
- Hits: 6419
Game controllers are pretty sophisticated these days. If you've seen the DJ Hero controller, you may wonder how it works. There's a 45-RPM-record-sized turntable for "scratching" which rotates freely which includes 3 pushbutton switches on the rotating piece. Obviously, the turntable rotation is read with some kind of encoder but how the switches are read is a mystery. I recently came across one of these at the right price, so with screwdrivers at the ready, let's delve into the internals.
The platter rotates very freely. With a good spin, it will rotate at least 10 turns before it slows to a stop. There's no resistance from any mechanical linkage between the platter and the base. The "controller" snaps on to the side of the turntable part through a somewhat complex mechanical linkage with includes a 4 pin connector.
Time to break out the screwdriver and see what's inside. Torx-head screws are used to hold the HJ Hero together, so a multi-bit set is helpful. I think there were nine screws holding this together - it looks like they expect it to take some abuse! The picture below shows the inside view of the top of the assembly. The bottom contains only the interface connector. This was a bit odf a surprise.
six wires run to the top half of the enclosure. Removing the four screwa around the center area allows the platter secttion to be lifted off.
Wow, that's hard to believe. None of the active parts are located in the stationary part of the assembly. A picket-fence around of the perimeter of the base for an encoder.
There's an optical gap sensor in the rim of the platter.
At the center of the platter is a slip ring assembly to permit transferring of power and signals between the rotating pieces. This is actually surprising as sling ring technology used to be extremely expensive.
The next step was to remove some more screws to open the platter section. Here's the top of the slipring assembly. Yes, it looks like the same wires that go into the bottom but there's actually a contact arrangement in the assembly.
Not much else is visible except for a circuit board containing the optical encoder and a circuit board for the switches.
There are 4 conductors in the cable between the switch board and the encoder board makes sense. Six wires lead between the encoder board and slip ring assembly. Hmmm... I'm suspicious about what's happening on the encoder board.
Bingo. A microcontroller was hiding on the bottom of the encoder board! And look at that! MCLR | VDD | GND | DAT | CLK... a standard PIC ICSP connector! I suspect the micro is a custom-programmed standard 28-pin part. This could lead to an interest project.