Nuts and Volts - November 2008

linearization, and temperature compensation. Outputs a signal proportional to air pressure.

• 16-bit Analog-to-Digital Converter — Transforms the analog info from the sensor into the necessary digital representation for further processing by the microcontroller.

• Microcontroller — Eight-bit 8051 with onboard Flash and RAM. Reads the A/D, calculates altitude from pressure, displays the altitude, and records to EEPROM (electronically erasable programmable read-only memory).

• LCD Display — Four-digit LCD with inter-integrated circuit interface.

• 32K EEPROM — For storing recorded altitude data.

• USB/Serial Converter — Interface to PC or external microprocessor for configuring, reading/writing altitude data, logging real-time altitude, etc.

• Buttons — Allow user to configure the altimeter setup using the LCD.

• LEDs — Indicate USB link, power, recording on, and flashes with each sample.

• Voltage Regulator — Converts input voltage to regulated 3.3V for the system. Takes input either from the USB port if attached or an external battery (or R/C receiver channel).

^Dimensions^1.57” ^x ^0.92” ^x ^0.37” 40 mm x 23. 4 mm x 9. 4 mm

Weight Eight grams

^Temperature ^Range¹^{0°C– 60°C} ^(pressure ^sensor ^±1.5% ^accuracy)- 10°C– 60°C (pressure sensor ± 3.0% accuracy)

Input Voltage Range 4.0– 30.0 volts DC

Input Current 16 milliamps (backlight on). 13 milliamps (backlight off).

Measured: 52,000 feet ( 15,849 meters)

Maximum Altitude¹Displayed: 9,999 feet/yards/meters

Recorded: 32,767 feet ( 9,987 meters)

Measured (absolute): -2,000 feet (-656 meters)

Minimum Altitude¹Displayed (relative or absolute): -999 feet/yards/meters Recorded (relative or absolute): - 32,512 feet (- 9,909 meters) Memory Capacity 16,378 samples

Acquisition 100 milliseconds/sample up to one hour/sample in Sampling Rates 100 millisecond increments

Timing Accuracy ±2.5%

Altitude Resolution One foot (one meter)

¹Specifications taken from component ratings and system limits; may not have been tested to the full extent of the specified ranges. ■ FIGURE2

altitude and maximum altitude. The display differentiates the two by flashing the maximum altitude. The maximum altitude is the greatest altitude recorded since the module was turned on.

• Zero Altitude — The current altitude to be set as the zero point with all subsequent readings being relative to that point.

• Recording Start/Stop — Store altitude data in memory. The number

of data sets is limited only by the amount of free data storage memory available.

Config Mode

Config mode allows the module to be configured using the two pushbuttons.

• RATE — This option selects the sampling period.

• CLR — This command clears

Figure 4 is a representation of the placement of all of these components.

Operation

The module operates in one of three modes, depending on the position of the pushbutton switches at startup. These modes are shown in Table 1.

Normal Mode

Normal mode is how the module will be used most of the time. In this mode, the module continuously displays altitude. The display updates four times per second. Note that this does not necessarily correlate to the sampling period. The following controls are available in normal mode: