HMR3100 allows users to derive compassing (heading) measurements when the board is in a reasonably horizontal (flat) position. The HMR3100 circuit starts with the HMC1022 two-axis magnetic sensors providing X and Y axis magnetic sensing of the earth’s field. These sensors are supplied power by a switching transistor to conserve power with battery operated products.
The power supply for the HMR3100 circuit board is to be about a +3 to +5 volt range allowing the user to provide a single lithium battery to logic level supply voltages. The power supply architecture is a single ground system for single ended supply sources (+ and ground return).
J4 is for Y-axis inversion should the end-item mount of the HMR3100 module be upside down (pins up). The HMR3100 sends data via the TXD line (Pin 5) in standard serial bus form at logic levels, but uses the RTS (Pin 3) and RXD (Pin 6) to select the three active modes of operation.
Calibration Mode When the host processor pulses low the RTS pin, and sends the RXD pin to a low logic level, the HMR3100 is in hard-iron calibration mode. This calibration is only for nearby magnetized metals (hard-iron) that are fixed in position with the HMR3100.
HMR3100 daughter-board. A nine-volt battery clip is included, but other DC input voltages between 7 and 15 volts may be used. Supply currents are nominally around 8mA plus the HMR3100 current draw. The RS-232 motherboard also contains a six-contact modular jack (RJ-11) for a compact RS-232 interface to a personal computer serial port.
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SENSOR PRODUCTS Honeywell reserves the right to make changes to improve reliability, function or design. Honeywell does not assume any liability arising out of the application or use of any product or circuit described herein; neither does it convey any license under its patent rights nor the rights of others.