BASIC DEVICE OPERATION
The HMR3500 TruePoint™ Compass Module includes 3-axis Anisotropic Magneto-Resistive (AMR) sensors, 3-axis
MEMS accelerometers, a temperature sensor, and 16-bit microprocessor with onboard Analog to Digital Converter (ADC).
The HMR3500 is available as a printed circuit board assembly, or assembled in a black aluminum case with cable
assembly. Additionally, the cable assembly can be ordered separately. A demonstration kit of the HMR3500 is available
with the case, cable assembly, a CD of the CompassHost windows utility software for the user's personal computer.
The HMR3500 requires an external DC power supply for the red (positive) and black (ground) wires of the cable
assembly. By feeding 5 volts at about 50 milli-amperes into the HMR3500, the compass will operate, and a red LED on
the printed circuit board assembly will begin blinking at a 1Hz rate. Lack of a blinking LED or at a rapid rate is an
indication of an error, and action should taken to cycle power on the compass electronics to reset the module.
As a factory default, the RS-232 interface is set at 9600 baud with one start bit, 8 data bits, one stop bit, and no parity bits.
The HMR3500 does not require any hardware or software handshaking or related features. The baud rate can be
changed by command after initial communication at the current baud rate.
The CompassHost utility software is a 32-bit Windows® application program that is provided with the HMR3500
demonstration kit, and can be used to evaluate the HMR3500's performance and demonstrate the compass features. With
exception of the baud rate change command, the CompassHost is capable of sending and receiving all of the commands
of the compass/computer interface. Host computers should be capable of running Windows 9x, ME, NT, 2000, XP and
follow-on operating systems. An install program loads the executable file CompassHost.exe and ActiveX components. A
readme.txt file is also included to describe the installation process.
The circuit board for the HMR3500 is 1.57 by 1.97 by 0.52 inches and composed of multi-layer, fiberglass-epoxy printed
boards, with the main board horizontal and a vertical board for mounting the z-axis magnetic sensor and accelerometer.
The vertical board is held orthogonal to the main board by two brass hardware blocks to ensure mechanical orthogonality.
Power Supply Return and Ground Reference
RS-232 Receive Data
RS-232 Transmit Data
Positive Power Supply Voltage Input
Ground Reference (for twisted pair routing with +Vin)
HMR3500 Top View and Dimensions