Circuit Description - Honeywell hmr3000 TruePoint User Manual

HMR3500 User's Guide
2.6.2 Case Dimensions (in inches)

2.7 CIRCUIT DESCRIPTION

The HMR3500 circuit design starts with a microprocessor powered by power supply sub-circuit that takes the input
voltage and creates regulated power for the various other circuits in the HMR3500. Two 2-axis MEMS accelerometers are
mounted horizontally and vertically to combine into a 3-axis tilt sensing sub-circuit. Each accelerometer outputs a Pulse-
Width-Modulated (PWM) digital signal that the microprocessor measures for pitch and roll angles.
Besides an integral temperature
sensor, a 2-axis and
magnetic sensor devices
mounted horizontally and vertically
to create a 3-axis measurement of
the incident magnetic field upon
the sensors. Each sensor output is
amplified and sent to a multiplexed
input ADC residing inside the
microprocessor. After
the magnetic signals are corrected
for hard and soft-iron magnetic
errors created by the environment
to which the compass is attached.
Heading computation uses the
magnetic and tilt information inputs
after compensation for
From the basic magnetic heading,
a declination value may be added
to arrive at a geographic north
referenced heading.
offset value may also be added to
correct for mechanical installation
misalignment on the
platform.
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1-axis
are
digitizing,
Magnetic Magnetic
Sensors Sensors
errors.
An index
target
Figure 2
Case Dimensions
Temp Temp
Sensor Sensor
X X
Y Y
Z Z
Power Power
Supply Supply
16 – Bit 16 – Bit
Microcontroller Microcontroller
Figure 3
HMR3500 Block Diagram
T T
RS-232 RS-232
I/O I/O
R R
X X
Y Y
Accels Accels
Z Z
5