Nuts and Volts - July 2014

Some years after that purchase, I met a guy named Lou from Camera Turret Company. He wanted to build his own focus and zoom controller, but didn't have the requisite embedded design or programming skills. At the time, I had just transitioned from Parallax to EFX-TEK where I was developing a lot of products using the SX microcontroller, doing my programming in a mix of SX/B (BASIC) and SX assembly.

It took a few weeks, but we had a working prototype. Sadly, that product never went into production. Still, it did whet my appetite for LANC. This past January, Lou called and asked if it would be possible to do LANC with the Propeller. Of course!

We pulled it off with the SX, so we can easily do that with the Propeller. In fact, we can do a whole lot more than we accomplished the first time around.

Under the Hood of LANC

LANC (Local Application Control Bus; a.k.a., Control-L) has been available for quite a long time; hence, is very simple. From the hardware point of view, LANC is an open-collector serial connection that runs at a very tame 9600 baud. The camcorder transmits an eight-byte packet to the controller 60 times per second (NTSC systems). Figure 1 shows the make-up of the LANC packet. Here's the neat part: The first two bytes of the packet are always $FF, and the camcorder reads these back as it's transmitting them. If a connected controller wants to pass a command to the camcorder, it simply modifies these bytes.

But how? As I just stated, the connection between the camcorder and controller is open-collector. What this means — as in I2C that we covered last time — is the serial connection is pulled high through a resistor; this sets the idle state and "1" bit state of the line. If either side wants to create a "0" bit, it pulls the line low. As in I2C, neither side can drive the line high; that is always left to the pull-up. Yes, LANC is just serial data, and pretty slow at that. We've created software UARTs with the Propeller many times, so this one won't be a lot of work.

Getting Connected

Figure 2 shows a very simple circuit for connecting the Propeller (or any other 3.3V micro) to the LANC line. If it looks familiar, you may remember it from the Dynamixel project we did last fall. Yes, this is a very simple bi-directional 3.3V to 5V level shifter; this circuit is

Getting Fancy With LANC

I think most of my regular readers know that my life is pretty evenly split between technology and entertainment — though a good bit of my technology work is for the entertainment industry. Having been inspired by the Robert Rodriguez book,

Rebel Without a Crew, I bought my first serious camcorder (Sony VX-1000) and learned how to shoot and edit video. One of the first accessories I purchased was a zoom and focus controller that plugged into the LANC (pronounced LAN-see) port of the camera. Every time I looked at that little port I thought, "What else could I do with this?"