CS4192_05 Datasheet, PDF (5/8 Pages) ON Semiconductor – Single Air−Core Gauge Driver

CS4192
APPLICATIONS INFORMATION
THEORY OF OPERATION
The SACD is for interfacing between a microcontroller or
microprocessor and air−core meter movements commonly
used in automotive vehicles for speedometers and
tachometers. These movements are built using two coils
placed at a 90° orientation to each other. A magnetized disc
floats in the middle of the coils and responds to the magnetic
field generated by each coil. The disc has a shaft attached to
it that protrudes out of the assembly. A pointer indicator is
attached to this shaft and in conjunction with a separate
printed scale displays the vehicle’s speed or the engine’s
speed.
The disc (and pointer) respond to the vector sum of the
voltages applied to the coils. Ideally, this relationship
follows a sine/cosine equation. Since this is a transcendental
and non−linear function, devices of this type use an
approximation for this relationship. The SACD uses a
tangential algorithm as shown in Figure 2. Only one output
varies in any 45 degree range.
0°
Max(128)
SIN+
Output ^Min(0)
Max(128)
SIN−
Output ^Min(0)
Degrees of Rotation
45° 90° 135° 180° 225° 270° 315° 360°
Max(128)
COS+
Output
Min(0)
Max(128)
COS−
Output _Min(0)
000 001 010 011 100 101 110
MUX bits (D9−D7)
Figure 2. SIN, COS Outputs
111 000
Quadrant I
ƪ ƫ q + Tan−1
VSIN₎
VCOS₎
* VSIN_*
* VCOS_*
Quadrant II
ƪ ƫ q + 180°−Tan−1
VSIN₎
VCOS₎
* VSIN_*
* VCOS_*
For q + 90.176°to 134.824° :
VSIN + 0.748 VBB
VCOS + *Tan (q * 90°) 0.748
VBB
For q + 135.176°to 179.824° :
VSIN + Tan(180° * q) 0.748
VCOS + *0.748 VBB
VBB
Quadrant III
ƪ ƫ q + 180° ) Tan−1
VSIN₎
VCOS₎
* VSIN_*
* VCOS_*
For q + 180.176°to 224.824° :
VSIN + *Tan (q * 180°) 0.748
VCOS + *0.748 VBB
VBB
For q + 225.176°to 269.824° :
VSIN + *0.748 VBB
VCOS + *Tan (270° * q) 0.748
VBB
Quadrant IV
ƪ ƫ q + 360° * Tan−1
VSIN₎
VCOS₎
* VSIN_*
* VCOS_*
For q + 270.176°to 314.824° :
VSIN + *0.748 VBB
VCOS + Tan(q * 270°) 0.748
VBB
For q + 315.176° * 359.824° :
VSIN + *Tan (360° * q) 0.748
VCOS + 0.748 VBB
VBB
For q + 0.176°to 44.824° :
VSIN + Tanq 0.748 VBB
VCOS + 0.748 VBB
For q + 45.176°to 89.824° :
VSIN + 0.748 VBB
VCOS + Tan(90° * q) 0.748
VBB
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