HMR3400 Datasheet, PDF (3/9 Pages) Honeywell Accelerometers – Digital Compass Solution

HMR3400
BASIC DEVICE OPERATION
The HMR3400 Digital Compass Solution includes all the basic sensors and electronics to provide a digital indication of
heading. The HMR3400 uses three magnetic sensors plus a MEMS accelerometer to provide tilt (pitch and roll) sensing
relative to the board’s horizontal (flat) position.
The HMR3400 circuit starts with Honeywell HMC1022 and HMC1021Z magnetic sensors providing X, Y, and Z axis
magnetic sensing of the earth’s field. These sensors are supplied power by a constant current source to maintain best
accuracy over temperature. The sensor output voltages and constant current sensor supply voltage are provided to
multiplexed Analog to Digital Converter (ADC) integrated circuit. A microcontroller integrated circuit periodically queries
the multiplexed ADC and performs the offset corrections and computes the heading. This microcontroller also performs
the external serial data interface and other housekeeping functions such as the calibration routine. An onboard EEPROM
integrated circuit is employed to retain necessary data variables for best performance.
An additional pair of data inputs from the ±2g accelerometer is received by the microcontroller. These tilt inputs (pitch and
roll) are added to sensor data inputs to form a complete data set for a three dimensional computation of heading.
The power supply for the HMR3400 circuits is regulated +5 volts allowing the user to directly provide the regulated supply
voltage to minimize PCB size. The power supply distrbution is a dual ground (analog and digital) system to control internal
noise and maximize measurment accuracy.
PHYSICAL CHARACTERISTICS
The circuit board for the HMR3400 Digital Compassing Solution is approximately 0.6 by 1.5 inches. An 4-Pin header may
optionally be placed at the edge connector plated through holes for pinned user interface. Figure 1 shows the typical
circuit board with dimensions.
1.50
1.00
0.065
0.60
0.30
Dimensions in inches
0.076 DIA (3 places)
MOUNTING CONSIDERATIONS
0.055 (2 places)
Figure 1
The following is the recommend printed circuit board (PCB) footprint for the HMR3400. Th ree small mounting holes are
provided to hold the HMR3400 mechanically to the host PCB or chassis. The goal is to hold the part horizont al and
parallel with the forward and side surfaces of the end product.
The HMC1021Z part is an 8-pin SIP device that is shipped carefully in a nearly perfectly vertical orientation with respect to
the horizontal referenced circuit board. Do not bend or reposition this part, or the factory magnetic calibration will be no
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