Servo - September 2010

consumption figure allows the Wasp electronics to run powered only by a single 3. 3 volt coin cell.

The Wasp design is similar in thought to that of the military Humvee. There are many roles this robotics processor can take on depending upon how it is equipped and configured. For instance, the Wasp is perfect for data logging missions as it can be programmed to store analog-to-digital readings into its internal EEPROM or external serial Flash. It can be loaded with serial Flash parts that range from 512K to 8M of eight-bit storage. The ATmega644’s ability to support an external 32.768 kHz clock crystal further adds to the Wasp’s data logging prowess as data logging can be tied to time of day or timed events via the ATmega644’s real time clock. In addition, the Wasp can sleep until the real time clock awakens the ATmega644 to take a reading.

SPI and I2C portals are common to most microcontrollers and the ATmega644 is no exception. The Wasp uses the services of the ATmega644’s SPI portal to communicate with the serial Flash. Atmel’s acronym for I2C is TWI (Two Wire Interface). The Wasp utilizes TWI architecture to communicate with other I2C-based smart peripherals. The Wasp’s I2C portal consists of a male Molex connector that also is pinned to power or be powered by external I2C devices. The Wasp can run at 3. 3 volts or 5.0 volts. When external serial Flash is installed, it is recommended to power the Wasp at 3. 3 volts to avoid releasing the serial Flash IC’s magic smoke. The only way to fly the Wasp with a 20 MHz crystal is to power the silicon polistes exclamans with 5.0 volts.

Another peek at Photo 1 reveals the presence of 8 Mbytes of serial Flash. I flipped the Wasp over in Photo 2 to show you the Freescale Semiconductor MMA7260 three-axis accelerometer IC. The smaller IC just above the MMA7260 is a Burr-Brown DAC8501 digital-to-analog converter IC. Both the MMA7260 and DAC8501 are optional components. In that the serial Flash and accelerometer are installed, the crystal you see in Photo 1 must be a 10 MHz part.

Photos 1 and 2 tell us what stuff the Wasp is made of. However, Figure 1 provides a detailed view of the Wasp’s I/O subsystem and power assignments. When the Wasp isn’t sitting on its nest, the SPI portal on digital port J2 can be used to program the Wasp’s AVR. Note that the AVR’s UART interface (RXD and TXD) is located on digital port J3 along with the pinned out I2C portal (SCL and SDA).

In the old days of the EDTP ATA hard drive controller, the AVR wanted to see a 10-pin ICSP termination. These days, the latest AVRISP mkII is fitted with a six-pin ICSP termination. The Wasp I received

PHOTO 1. This is a Wasp. Instead of a stinger, wings, big eyes, and six legs, you’re looking down on an Atmel ATmega644

microcontroller, 8 MB of Atmel serial Flash, a 10 MHz CPU crystal, a 32.768 kHz real time clock crystal, and various capacitors and resistors. The Molex connector is a powered I2C portal.