The RDCM-803 Digital Compass Module Introduction The RDCM-803 Digital Compass Module is a miniature low-cost orientation-sensing building block. It indicates the orientation of the module relative to magnetic-north, as one of sixteen directions. This is a successor to the RDCM-802 Digital Compass Module, and may be used to replace it. Features • Miniature size 26.3 x 26.3 mm (1.035 x 1.035 inches) • Low power 3 mA typical, plus whatever current is sourced from the direction output pins. • Wide supply voltage range Can operate from 2.6 to 5.6 V. • Easy to interface to Output is via four pins, indicating a 4-bit binary value. “Grey encoding” is used, to ensure only one bit changes between any two adjacent directions • No moving parts The RDCM-803 is entirely solid state, making it very robust • Backward compatibility The RDCM-803 can replace the earlier RDCM-802 8-direction compass module, with no circuit changes. • Improved performance Compared to the RDCM-802 module, the RDCM-803 is: o More precise: 16 directions, compared to 8. o More accurate: ± 3 °, compared to ± 5 ° o More tilt tolerant: ± 60 °, compared to ± 10 ° o Lower power: 3 mA, compared to 10 mA. Mechanical Dimensions Pinout Name Direction +5V +3V GND D0 D1 D2 D3 STB In In Out Out Out Out Out RDCM802 equivalent +5V GND D0 D1 D2 D3 - Description Power input. 3.8V to 5.6V Alternate power input. 3.3V ±5% Power and reference ground Direction output (Most significant bit) Direction output Direction output Direction output (Least significant bit) Idles high. Switches low while a measurement is being taken, then switches high immediately after the direction output pins are updated. MODE In Mode select. Pulled down internally. Low RDCM-802 compatible (Magnetic North offset by 22.5° for 8 directions, or 11.25° for 16 directions.) High Zero offset mode (for 16 directions only) Note: The lightly shaded pins are new to the RDCM803 model. If left un-connected, the RDCM803 behaves the same as an RDCM802. Absolute maximum ratings Parameter Voltage on 5V with respect to GND Limits -15 V to +6.5 V Voltage on 3V with respect to GND -15 V to +4.8 V Voltage on MODE with respect to GND -0.3 V to 5V (when powered via 5V pin) (i.e. the voltage on the 5V pin) Voltage on MODE with respect to GND -0.3 V to 3V (when powered via 3V pin) (i.e. the voltage on the 3V pin) Direction Indication With MODE pin low (i.e. RDCM-802 compatible mode) 8 directions To detect 8 directions (the same as an RDCM-802), use just D2, D1, and D0 The angles in this table represent degrees clockwise from the arrow on the PCB, to magnetic north. D2 0 0 1 1 0 0 1 1 D1 1 1 1 0 0 0 0 1 D0 1 0 0 0 0 1 1 1 Dir N NE E SE S SW W NW Start angle 0 45 90 135 180 225 270 315 End Angle 45 90 135 180 225 270 315 360 = 0 So, to make north straddle your reference direction, the reference should be rotated 45/2 = 22.5 degrees clockwise from the arrow. 16 directions To detect 16 directions, observe D3 as well. This then divides each direction in half. With MODE pulled low D3 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 D2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 D1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 D0 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 Dir N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Start 0 22.5 45 67.5 90 112.5 135 157.5 180 202.5 225 247.5 270 292.5 315 337.5 End 22.5 45 67.5 90 112.5 135 157.5 180 202.5 225 247.5 270 292.5 315 337.5 360 = 0 To make north straddle your reference direction, it should be rotated 22.5/2 = 11.25 degrees clockwise from the arrow. With MODE pin pulled high (i.e. RDCM-803 native mode) Pulling the MODE pin high rotates the reference frame so that north DOES straddle the reference arrow on the PCB. The 4 bit code for North will be output if magnetic north is 11.25 degrees either side of the reference arrow. D3 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 D2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 D1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 D0 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 Dir N NNE NE ENE E ESE SE SSE S SSW SW WSW W WNW NW NNW Start 348.75 11.25 33.75 56.25 78.75 101.25 123.75 146.25 168.75 191.25 213.75 236.25 258.75 281.25 303.75 326.25 End 11.25 33.75 56.25 78.75 101.25 123.75 146.25 168.75 191.25 213.75 236.25 258.75 281.25 303.75 326.25 348.75 Example usage Minimum configuration, to display 8 directions on LEDs (RDCM-802 compatible mode.) Interfaced to a microcontroller. 16 directions with zero offset for north. rdcm803 jul-2013