sampling the amplified output from a
magnetoresistive sensor that is used to
measure the vertical component of
the Earth’s magnetic field in order to
detect when the rocket tips over at
apogee. Honeywell and Phillips produce devices that have the required
0.5 gauss sensitivity for this task (but
the output signal would have to be
amplified before feeding the ADC).
By comparing the recorded
magnetic field strength and vertical
acceleration data, it should be possible
to measure any delay between apogee
and nose cone ejection. This information will help determine the engine
delay charge required to deploy near
the rocket’s minimum speed, in order to
reduce the risk of damaging the chute.
Having employed all three of the
flight recorder’s ADC channels in the
above examples, we still have the
option of interfacing sensors via the
sensor port’s serial I2C bus. A good
example of an I2C compatible smart
sensor is the SCP1000 barometric
pressure IC from VTI Technologies.
Pressure and temperature output data
are calibrated and compensated
internally. This device operates from a
2.4V- 3.3V supply and has the potential to provide a more accurate altitude profile than could be derived by
integrating vertical acceleration data.
The SHT11 humidity and temperature IC from Sensirion AG is another
smart sensor that has a two-wire serial
bus. However, it is not I2C compatible
and would have to be interfaced by
‘bit banging’ sensor port I/O lines.
This device operates from a 2.4V- 5.5V
supply and the output data is calibrated and compensated internally. It
could be used to study microclimates
by measuring the relative humidity
and temperature of a column of air
(e.g., to obtain a profile through a
layer of mist). However, because the
sensor’s update rate is in the order of
seconds, measurements are best
taken during a slow descent under a
With the exception of the sun and
magnetoresistive sensors, all the
above examples could be connected
directly to the sensor port without
additional signal conditioning or
power supply circuitry.
The flight recorder is a compact
and low power instrumentation tool
that can be rapidly configured to
accommodate a range of applications.
In addition, the use of SelmaDAQ
makes spreadsheet data import,
processing, and display an almost
seamless task. NV
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