HMC1051/HMC1052/HMC1053
www.honeywell.com 7
current of 400mA for reset or set pulses. With rare exception, the set/reset strap must be used to periodically condition the
magnetic domains of the magneto-resistive elements for best and reliable performance.
A set pulse is defined as a positive pulse current entering the S/R+ strap connection. The successful result would be the
magnetic domains aligned in a forward easy-axis direction so that the sensor bridges polarity is a positive slope with
positive fields on the sensitive axis result in positive voltages across the bridge output connections.
A reset pulse is defined as a negative pulse current entering the S/R+ strap connection. The successful result would be
the magnetic domains aligned in a reverse easy-axis direction so that sensor bridges polarity is a negative slope with
positive fields on the sensitive axis result in negative voltages across the bridge output connections.
Typically a reset pulse is sent first, followed by a set pulse a
few milliseconds later. By shoving the magnetic domains in
completely opposite directions, any prior magnetic disturbances
are likely to be completely erased by the duet of pulses. For
simpler circuits with less critical requirements for noise and
accuracy, a single polarity pulse circuit may be employed (all
sets or all resets). With these uni-polar pulses, several pulses
together become close in performance to a set/reset pulse
circuit. Figure 1 shows a quick and dirty manual pulse circuit for
uni-polar application of pulses to the set/reset strap.
APPLICATION NOTES
Low Cost 2-Axis Compass
Very high precision measurements can be made using the HMC105X family of sensors when interfaced with low noise
amplifiers and 12 to 16-bit Analog-to-Digital (A/D) converters. For lower resolution (3?accuracy or more) or low cost
compass applications, 8 or 10-bit A/D converters may be used with general purpose operational amplifiers. Figure 2
shows a typical 2-axis compassing application using readily available off-the-shelf components.
The basic principle of two-axis compassing is to orient the two sensor bridge elements horizontal to the ground
(perpendicular to the gravitational field) and to measure the resulting X and Y analog output voltages. With the amplified
sensor bridge voltages near-simultaneously converted (measured) to their digital equivalents, the arc-tangent Y/X can be
computed to derive the heading information relative to the X-axis sensitive direction. See the application notes on
compassing at Honeywell Magnetic Sensors website (www.magneticsensors.com) for basic principles and detailed
application information.
Figure 1
Set Pulse Circuit
HM C 1 0 5 2
U1
V cc
o ffse t
se t/re se t
.1 u f
(2 ) IR F 7 5 0 9
se t/re se t
_ se t/re se t
V re f/2
V re f/2
5 .0 0 k
5 .0 0 k
5 0 0 k
5 0 0 k
5 .0 0 k
5 .0 0 k
5 0 0 k
5 0 0 k
LM V 3 5 8
L M V 3 5 8
1 n f
1 n f
M A X 1 1 1 8
1
0
V re f
U 2
U 3
U 4
U 5
e n a b le
d a ta _ o u t
clk_ in
2 .5 to 3 .6 v
H M C 1 0 5 2
U 1
V cc
o ffse t
se t/re se t
.1 u f
(2 ) IR F 7 5 0 9
se t/re se t
_ se t/re se t
V re f/2
V re f/2
5 .0 0 k
5 .0 0 k
5 0 0 k
5 0 0 k
5 .0 0 k
5 .0 0 k
5 0 0 k
5 0 0 k
L M V 3 5 8
L M V 3 5 8
1 n f
1 n f
M A X 1 1 1 8
1
0
V re f
U 2
U 3
U 4
U 5
e n a b le
d a ta _ o u t
clk_ in
2 .5 to 3 .6 v
Figure 2
Two-Axis Compass
Is  e  t
5   v  o  l t s
I s  e  t
5   v  o  l t s