♪ Control ♪
Hello.
Today we have a first look at
the SM124 Smart GMR Magnetometer,
which combines the precision of Giant Magnetoresistance
with slick Digital Signal Processing.
We have a ridiculously simple evaluation board.
A microcontroller communicates with the SM124 sensor via I²C
and with a PC via USB.
There's also an LED to show the digital threshold output,
and a trace under the sensor for current sensing.
To show its precision as a proximity sensor,
We have an Arduino driving a linear stepper motor
to move a magnet back and forth between sensor thresholds.
Here's the Arduino program,
which uses the sensor's threshold output.
We could use the Arduino to program the sensor via I²C,
but we wanted to show the fancy-pancy user interface
for this demo.
The beauty of this sensor
is that once you set the digital threshold,
the output can operate without I²C.
The Arduino homes the magnet as close as possible,
which is four millimeters
from the edge of the magnet to the center of the sensor.
The Arduino reports the switching positions.
With the four oersted default threshold,
the sensor turns on at 26.5 millimeters and off at 29,
with a tenth-millimeter repeatability.
We set the threshold higher-- 12 oersteds...
and it turns on at 33 millimeters and off at 34.
We can even set a threshold of just one oersted...
...to detect the magnet nearly 50 millimeters away.
And it's remarkably stable, even with such a small field.
In additon to the "Main" and "Settings" tabs,
a "Memory" tab lets us examine and modify the sensor's memory.
The data is all single-byte for unmatched simplicity,
and seamless interfacing to eight-bit microcontrollers.
And we still have better than 1% precision.
The SM124 can be used as a noncontact current sensor.
When we run a current
through the trace on the demo board,
we can see the sensor output on the computer.
The digital threshold output
indicates overcurrent,
in this case at five amps.
Taking a closer look at the SM124 sensor:
• a GMR sensor element;
• an ADC;
• temperature compensation;
• a clean, single-byte I²C interface; and
• a programmable digital threshold output.
SM124 features include:
• 0 to 15 Oe field range,
so it can detect magnets more than 50 mm away;
• it's omnipolar, so you don't have to worry about magnet polarity;
• it's accurate;
• it has a slick, single-byte I²C interface;
• more than ten thousand samples per second;
• the full industrial / automotive temperature range;
• and it's ultraminiature.
Call, click, or e-mail us for more information,
or to buy SM124 sensors and evaluation kits.