Data Sheet
LINEAR MAGNETIC FIELD SENSORS
12
Simple Circuit Application
The circuit in Figure 16 shows a simple application of a
magnetic sensor. This circuit acts as a proximity sensor
and will turn on the LED when a magnet is brought within
0.25 to 0.5 inch of the sensor. The amplifier acts as a
simple comparator and switches low when the HMC1001
bridge output exceeds 30mV. The magnet must be
*R
1 or
R
2 use
d
to tr
i
m o
ff
est
**R3 = 451Ω for 1 axis, 921Ω for 2 axis, or 1411Ω for 3 axis
# provides 1KHz rolloff
V
re
f
Magnetic
Sensor
1.5n
F
#
650
R
1
*
R
2
*
-
+
25
K
LM
440
2.5V
V
+
AMP04
HMC1001
V
out
1
8
6
5
2
3
Ai
n+
Ai
n-
R
e
f
+
R
e
f
-
CONV
SCLK
SDATA
NDRDY
XIN
CAL
NCS
1.6Ω
V
+
7
4
8
5
13
7
8
9
10
2
14
15
16
4
3
1
CS5509
16 bit A/D
12
G
n
d
V
+
6,11,13
+5
V
Serial Bus
Interface
+6-15
V
S
/
R
Pulse
10
-+
V
re
f
22.1
K
R
3
**
BS250
100
K
LMC7101
5 mA
0.01
1
34
Figure 18—One-Axis Sensor With Constant Bridge Current and Digital Interface
strong (200 gauss) and have one of its magnetic poles
point along the sensitive direction of the sensor. This
circuit can be used to detect a door open/closed status or
the presence or absence of an item. Figures 17, 18, 19,
20 and 21 show other circuit examples.
4
G
a
i
n=1000,
BW
=10
H
z
* R1 is used to trim switchpoint
# provides 10Hz rolloff
Magnetic
Sensor
0.15µ
F#
100
R
1
*
+
-
AMP04
HMC1001
1
8
6
5
3
2
7
4
8
5
+5
V
7
400
+5
V
C
a
lib
rate:
1. Trim R1 for (+V) - (-V) < 30mV
2. Apply signal < 30mV, LED should be off.
3. Apply signal > 30mV, LED should be on.
V-
V+
Vout
LED
magnet
movement
Figure 16—Magnetic Proximity Switch
*R
1 or
R
2 use
d
to tr
i
m o
ff
est
# provides 1KHz rolloff
V
re
f
Magnetic
Sensor
1.5n
F
#
650
R
1
*
R
2
*
-
+
25
K
LM
440
2.5V
V
+
AMP04
HMC1001
V
out
1
8
6
5
2
3
Ai
n+
Ai
n-
R
e
f
+
R
e
f
-
CONV
SCLK
SDATA
NDRDY
XIN
CAL
NCS
1.6Ω
V
+
7
4
8
5
13
7
8
9
10
2
14
15
16
4
3
1
CS5509
16 bit A/D
12
G
n
d
V
+
6,11,13
+5
V
Serial Bus
Interface
+5
V
S
/
R
Pulse
Figure 17—One-Axis Sensor With Digital Interface
Figure 19—One-Axis Low Cost Sensor
(1) Momentarily close switch SW1. This creates a SET pulse. (2) Measure bridge output (OUT+) - (OUT-) NOTE: Bridge
output signal will be 5mV/gauss (3) Measure Vout after AD623 amplifier (G~500) NOTE: Vout signal will be 2.5V/gauss
Sensitive
Direction
OUT-1
V
BRIDGE
2
S/R+3
GND4
S/R-5
O
FFSET+
6
O
FFSET-
7
OUT+8
HMC1021S
10K
4.7uF
tantalum
SW1
Vout
+5V
1M
-
+
A
MP623
200
+5V
2.5V
25K
LM404-2.5
+5V
Gnd
V+
Z