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Honeywell’s magnetoresistive sensors are utilized to provide enhanced reliability and accuracy in a small, two-axis, solid state compass design. This compass solution is easily integrated into systems using a simple UART interface and binary data format. Performance is optimized for a horizontal circuit board orientations. SPECIFICATIONS Characteristics Conditions Min Typ Max Units Heading Accuracy Level ± 5 deg RMS Resolution 0.5 deg Repeatability ± 3 deg Magnetic Field Range Maximum Magnetic Flux Density ± 2 gauss Resolution 6 milli-gauss Electrical Input Voltage Unregulated 2.6 3 5 volts DC Current Normal Mode (Average) Sleep Mode Calibration 0.1 6.1 0.2 7.3 0.5 1 17.3 mA .A mA Digital Interface USART USART 9600.N.8.1 2400 9600 19200 Baud Update Continuous or Polled -2 20 Hz Connector 8-Pin - Physical Dimensions Circuit Board Assembly 19 x 19 x 4.5 mm Weight 1.5 grams Environment Temperature Operating Storage 0 -40 - - +70 +110 °C °C Circuit Description The HMR3100 Digital Compass Solution circuit board includes the basic magnetic sensors and electronics to provide a digital indication of heading. The HMR3100 has a Honeywell HMC1022 two-axis magnetic sensor on board. The 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 sensor output voltages are provided to a dual operational amplifier and then to analog to digital Solid State Electronics Center • • (800) 323-8295 • Page 2 HMR3100 SENSOR PRODUCTS converters (ADC) onboard a microcontroller (.C) integrated circuit. The microcontroller integrated circuit periodically samples the amplified sensor voltages, 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. 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). Note the “North Arrow” printed on the HMR3100 circuit board top side. This is the mechanical reference for product alignment purposes. When placed on the development kit’s RS-232 motherboard assembly, this arrow also points toward the 9-volt batterypin block on the motherboard (away from the RJ-11 jack). Pin Configuration Description 1 VCC Power Supply Input 2 NC No Connection 3 RTS Ready To Send Input 4 NC No Connection 5 TXD Transmit Data Output 6 RXD Receive Data Input 7 GND Power and Signal Ground 8 NC No Connection The HMR3100 board is 0.77” on each side with eight pins in groups of four spaced at 0.6” apart in wide-DIP format. Seated height is approximately 0.275”. Pin 1 is the upper right pin in Figure 1 . Figure 1 HMR3100 Dimensions Solid State Electronics Center • • (800) 323-8295 • Page 3 HMR3100 SENSOR PRODUCTS USART Communication Protocol HMR3100 module communicates through binary data and ASCII characters at four selectable baud rates of 2400, 4800, 9600, or 19200. The default data bit format is USART 9600.N.8.1. The baud rate selection is determined by the position of jumpers J1 and J3. These jumpers are zero ohm SMT resistors (jumpers) and are normally high (logic 1) when removed, and grounded (logic 0) when in place. At 2400 baud, no jumpers are present for a 1,1 logic presentation. At 4800 baud J3 is present for a 1,0 logic presentation. The factory default setting of 9600 baud is created by a jumper present on J1 for a 0,1 logic presentation. With J1 and J3 jumpers present for a 0,0 logic presentation, the compass module works at 19200 baud. See Figure 1 for jumper locations. Jumper J2 is for factory testing, and 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. Normally RTS and RXD input lines are left high until data or hard-iron calibration is needed from the HMR3100. The RXD line is left high unless a calibration is requested. The RTS line will be either be pulsed low or held low to initiate an active mode. Otherwise a low-power sleep mode is the default state. The RXD and RTS data inputs are passively pulled high via the microcontroller if left open. Normal Mode When the host processor (external to the HMR3100), sends a RTS low pulse to the RTS pin, the HMR3100 will send status/heading data via the TXD pin. The host shall hold the RXD pin high during this mode. The RTS shall ...