HMR3500 User's Guide
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 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.
2.6 PHYSICAL CHARACTERISTICS
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.
2.6.1 Mounting Considerations
The following is the recommend printed circuit board (PCB) footprint for the HMR3500. The reference direction (forward)
is the right PCB assembly edge shown in Figure 1. Left to right, the interface connector is numbered pin 1 to pin 5 per the
pin configuration table.
UNC 4-40 fastening hardware is recommended for mounting the printed circuit board with at least 0.125 inch nylon
spacers to stand off the board from the mounting surface. Fastener hardware must be non-ferrous for full compass
performance with brass or nylon screws the usual materials of choice.
Top View and Dimensions