Personally, I find this to be a sad state of affairs when an intelligent robot with SONAR vision is asked to behave like an RC car.   I’ve named this mode of operation “Slave Mode” to quietly voice my opinion on the matter.  It’s something like a zombie version of the same rover and you can understand why R2-D2 was so interested in getting rid of that restraining bolt in the first Star Wars movie so he could run for the hills.

For the record, I wrote a command interpreter for the Rover so you can send him into Slave mode with a Wi-Fi device, ZigBee, or even from his own web server.  Truly, he is not going to escape and run off to find Obi-Won Kenobi.

Adding ZigBee to the Rover… Scary Scary!

I admit that ZigBee is pretty intimidating but getting him up and running was less than a day with the Rabbit code.

The first thing you want to realize is that you can set up one of the ZigBee modems to fake out a serial port.  Why is that important?  It means my Rover doesn’t need to know “thing one” about ZigBee.  He just writes or reads with his serial port and the modem does all the work.  If there is no need to worry about the ZigBee software, I don’t increase my project’s code size and my CPU doesn’t have to carry the overhead either.

On the other end I have an RCM4510W acting as the ZigBee coordinator to the Rover’s ZigBee end device.  He comes up using our ZigBee API, sends off a command to set the Rover’s modem as a transparent serial port and then sits there listening as my rover happily chatters away to his fake serial port.  Little does he know that every log entry is being passed wirelessly to my other Rabbit where I can easily dump the data into a log file.

ZigBee at Play

In this video you can see our Rover happily face-planting into a cube wall while he reliably sends us a description of his many woes via the ZigBee connection back to my PC.

You will see an XBee Series 2 modem on the Rover in the video and in the image below.

You can see the blue ZigBee Modem on the PCB.

Jimmy Buffer steps up to the Microphone

We have 8 digital outputs from the Rabbit’s parallel port A that we need to shift from 0-3 volts up to 0-5 volts and we have determined experimentally that we are too lazy to solder 8 Op-Amps.

First, the buffer is a digital device so it will either output 0 volts or 5 volts (Vcc).  According to the buffer chip’s datasheet, it will read anything above 2 volts as a logical 1.  The Rabbit’s output at 3.3 volts will get bumped up to 5 volts by the buffer and that means “bye-bye” to the operational amplifiers.

Swapping out the Op-Amps with an 8-pin buffer

Adding Features

With the circuit already drawn up in DipTrace, it wasn’t tough to update it and add a few new features.

• Add some 50-pin headers so we can plug directly into the RCM5600W’s demonstration board
• Replace the 8 Op-Amps with a single bus driver chip
• Add one more voltage regulator so we have access to 12 volt, 5 volt, and 3.3 volt supplies
• Add a socket for an XBee ZigBee modem

Check out Larry’s blog entry for more details and the files used to create the circuit board.

The New Schematic

Schematic Version 1.1

The last item is a big feature addition.  The Rabbit already has 802.11g Wi-Fi built into the RCM5600W and we’re planning on using the embedded server to deliver web pages for controls and other functionality.  However, Wi-Fi is short range and if we were to hypothetically toss the Rover out of a plane at 30,000 feet his odds of finding a Wi-Fi connection aren’t great as he plummets to the earth.  It might be useful to have a long range wireless connection for commands like “deploy parachute“.

Some of the ZigBee modems like the XBee can have much higher range because they operate at lower frequency.   A high gain ZigBee device operating at 900 Mhz with good line of sight can reach a range of up to 6 miles.  We won’t be sending data quickly, but remote operation becomes a real possibility.

The New Fangled Custom Printed Circuit Board (PCB)

The Rover PCB

The Joy of Lazy

While it might seem like a bad thing to be too lazy to solder down 8 Op-Amps, we have actually reduced the complexity of the design and the overall production cost.  In embedded engineering a simpler design is generally better and a little laziness up front will save us plenty of work later if we decide to build an army of Rovers to conquer the earth.