Patent GB-1498443-A (GB)
Title: Digital solid state compass
IPC: G01C17/28
Filed: 1975-07-10
Abstract: 1498443 Solid state compass E SYSTEMS Inc 10 July 1975 [5 Aug 1974] 29068/75 Heading G1N A solid state compass comprises a clock oscillator 1 for generating clock signals at a predetermined frequency and timing signal generating means, e.g. a pair of divider circuits 5, 7 dividing by 360 Figs. 2, 3 (not shown), connected to the clock oscillator 1 and being responsive to signals therefrom to provide a reference signal and a plurality of timing signals Fig. 9 (not shown) in any one of a series of a predetermined number, e.g. 360, of clock signals. Driving means 9 are connected to the timing signal generating means 5, 7 and are responsive to the timing signals for providing during signals for during at least two Hall effect generating means, e.g. a heading sensor 15 and a transverse sensor 13, fixed in a mutual angular relationship the Hall effect generating means being operative for providing a  heading signal representative of an orientation angle between a direction of orientation of the Hall effect generating means and the magnetic north. Start signal generating means 37 are connected to the clock oscillator 1 and the timing signal generating means and are responsive to the clock signals and the reference signals for providing a series of start signals at a second predetermined frequency related to the first mentioned predetermined frequency, e.g. one start signal per series of 360 clock signals. A control circuit connects the Hall effect generating means 13, 15 and the clock oscillator 1 to a counter 43 and is responsive to each start signal, in use, to enable the counter to begin to count the clock signals until such time as the heading signal disables the counter, the count then being registered in the counter being representative of the aforesaid direction of orientation. Since, as abovestated, 360 clock signals are designated to every "cycle" the number of clock signals counted represent the orientation in degrees. The driving means 9 generates a cosine signed to the transverse sensor 13 and a sine signal to the heading sensor 15 of period equal to 360 clock signals by means of transistor switch circuits and oscillator circuits, each oscillator circuit comprising a capacitor and the primary winding of a transformer Fig. 4 (not shown). Two outputs 27, 29 of the sensors 13, 15 are cycled together such that the output of the transverse sensor 13 at terminal 31 comprises a sinusoidal wave having a period equal to 360 clock signals but displaced in time with respect to a start signal by an amount proportioned to the orientation to be measured. The output of sensor 13 is amplified and clipped to provide, after being correlated with reverse clock signals from the start signal generating means 37 in a stop signal generating means 35, a stop signal to provide the aforesaid disabling of the counter 43 via a counter enable circuit 39. From an inverse reference signal and an inverse start signal, an inverse strobe signal is produced on the start signal generating means 37, the inverse strobe signal also being fed to the counter enable circuit 39 to provide a timing pulse therefor Fig. 10 (not shown). The inverse stroke signal is provided immediately prior to a measuring cycle and a strobe signal from an inverter 47 is fed to a latch circuit 45 to trigger the storing of the number of counts counted in the cycle just ended, the next strobe signal causing the latch circuit to feed this count to a reedout 49 while storing the next count.