If you're like me, you keep asking the same question: "Why can't I talk to my toys with my PDA?" In this case, my "toy" is a Meade ETX-105 Maksutov-Cassegrain telescope.

The ETX-105 is a very cool, somewhat affordable high-resolution telescope with auto-tracking capability. This auto-tracking stuff sounds great, but to unleash its full potential you need to add another Meade option called Autostar. The addition of the Meade Autostar system turns your Meade telescope into an automatic celestial-object-locating system.

Autostar brings a very important feature into this system: an open-standard RS232 serial interface. Meade provides a detailed protocol specification so geeks like us can "kick it up a notch" with this interface port.

Now for the good stuff. If I have an RS232 port and all the info needed to control this port, what must I build to allow any handheld -- or PC running any OS -- to talk to my telescope?

Interplanetary PDA

There are a few things built into nearly every PC and handheld that I can use to pull off the feat.

• I see lots of IrDA (infrared data) ports.
• Just about every PC speaks TCP/IP.

What if we build a TCP/IP-to-Autostar RS232 bridge that can also talk over an IrDA link? This would allow us to control our Meade telescope with the Autostar, any Palm IrDA device, or any PC running a Web browser, even over an 802.11 or Bluetooth wireless option.

Even better, this also lets us control our telescope over the Internet. Bam!

Steven Pope is a fellow at ZiLog. He holds five U.S. patents, with a focus on embedded microcontroller hardware and software applications.