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♪ Circles and angles ♪

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Hello.
Today we're showing

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typical interfaces from
NVE's "AAT" angle sensors.

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to simple microcontrollers.

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We have two demos:
a simple 3-digit interface;

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and a more precise 4-digit demo.

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We use a radial magnet,
and there's an AAT angle sensor on this board.

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The sensor outputs
follow the sine and cosine

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of the magnet angle.

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There are several AAT Sensor versions
with different resistances.

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The AAT003 has 40 kilohm elements,
for a 20 kilohm output impedance,

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which is ideal for direct interface to
the analog inputs of simple microcontrollers.

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We're interfacing to an Atmel MEGA328
on an Arduino board.

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The first example is a 3-digit readout
for one degree resolution.

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We have an analog output from the micro,
connected to an inexpensive panel meter

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through a single-ended scaling voltage divider.

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The program uses the microcontroller's
built-in 16-bit timer/counter

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to produce a pulse-width modulated analog
output.

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This program uses a simple 10-bit PWM library,
which is fine for one-degree resolution.

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We initialize the PWM timer.
The main program is only one line,

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where we read two sensor outputs;
calculate the angle using a two-variable arctangent;

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we assume the outputs
are centered around half the supply;

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and we normalize the output
for five volts full scale,

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or 0.1 millivolts per degree
after the voltage divider.

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So here's the three-digit
interface in operation.

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Now let's look at a tenth of a degree resolution.
Since these inexpensive meters

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don't have a full four digits,
we'll run plus or minus 180 degrees

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to resolve a tenth of a degree
with a three-and-a-half digit readout.

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So the meter is set up in differential mode,
and the voltage divider is set for

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one millivolt per degree.

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Here are the meter connections--
just some jumpers and resistors.

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The input A-to-D's
of these basic micros are only 10 bits.

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Of course we could add a preamplifier,
but that increases cost and complexity.

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The AAT's large signal--

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typically one volt peak-to-peak,
with a five-volt supply--

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is enough for sub-degree precision
without amplification.

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We pick up resolution by using both the
sine and cosine outputs in the calculation.

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Also, we're averaging several
sensor measurements for each angle calculation

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to increase the effective resolution.

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For the output side,
this library routine takes full advantage

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of the microcontroller's
16-bit timer/counter

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for a high-resolution PWM output.

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We also have a simple calibration routine
to enhance accuracy.

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The routine records the range of each output.

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Those data are used to correct for
electrical offset,

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as well as sensitivity differences
between the two outputs.

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The blue LED indicates the calibration mode.
We just have to turn the magnet a few revolutions.

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Now we're in the measurement mode...

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and we have precise readings,
with no amplification.

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So, we've shown how AAT Sensors
easily interface to popular microcontrollers

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with a minimum of components.

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Click, email, or call us for more
information, or to order

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parts or demonstration kits.