Inductive Touch Sensing Keyboard Circuit

Figure shows an example for a 4-key Inductive Touch Sensing keyboard
with key controlled by the IO pins of the PIC® MCU.

The PIC® microcontroller is used to generate a squarewave signal and
to do all the necessary operations forproper detection of the key press event.

Then, RIN-CIN filter converts the square wave output ofthe PWM into
a quasi-triangular waveform.

To calculate the amplitude of the triangular signal, thestandard charging
time equation for an RC network willbe used

MCP2036
DescriptionThe MCP2036 Inductive Sensor Analog Front End(AFE)
combines all the necessary analog functions fora complete inductance
measurement system.The device includes :• High-frequency,
current-mode coil driver forexciting the sensor coil.• Synchronous detector
for converting AC sensevoltages into DC levels.• Output amplifier/filter to
improve resolution andlimit noise.• Virtual ground reference generator for
singlesupply operation.

Features
• Complete Inductance Measurement System:
- Low-Impedance Current Driver
- Sensor/Reference Coil Multiplexer
- High-Frequency Detector
• Operating Voltage: 2.7 to 5.5V
• Low-Power Standby Mode
• Gain and Frequency set by external passivecomponents

MCP2036 Datasheet pdf
http://ww1.microchip.com/downloads/en/DeviceDoc/22186A.pdf

Introduction to Inductive Touch Sensing Vedio

Introduction to mTouch Inductive Touch Sensing Part 1



Introduction to mTouch Inductive Touch Sensing Part 2

WIDER POSITION SENSING CIRCUIT

To go from 45° to 90° requires two HMC1501
sensors or a single HMC1512 dual sensor part. By
using two bridges with 45° displacement from each
other, the two linear slopes can be used additively.
Figure 8 shows a typical configuration.
From Figure 8, as the shaft rotates around, magnetic
flux from a magnet placed at the end of the shaft exits
the north pole and returns to the south pole. With a
HMC1512 placed on the shaft axis, just above the
magnet, the flux passing through the sensor bridges
will retain the orientation of the magnet. From this
rotation, the output of the two bridges will create sine
and cosine waveforms as shown in Figure 9.

Because the sine (sensor bridge A) and cosine
(sensor bridge B) will match after the offset error
voltages are subtracted, the ratio of bridge A to bridge
B creates a tangent 2O function and the amplitude A
values cancel. Thus the angle theta is described
as:

However because there are some trigonometric
nuances with the arctangent function when gets
close to _45° and beyond, these special cases apply:

Because most trigonometric functions are performed
as memory maps in microcontroller integrated circuits,
these kinds of special case conditions are easily dealt
with. The resultant angle theta is the relative
position of the magnetic field with respect to the
sensor. It should be noted that if rotation is permitted
beyond _90°, the theta calculation will replicate again
with postive and negative 90° readings jumping at the
end points. Further performance to 360° or _180° can
be mapped into a microcontroller by using this circuit
plus a Hall Effect sensor to determine which side of
the shaft is being positionally measured via magnetic
polarity detection. Figure 10 shows the basic circuit
interface for the HMC1512.

Source
http://www.ssec.honeywell.com/magnetic/datasheets/an211.pdf

HMC1501 / HMC1512
Linear / Angular / Rotary
Displacement Sensors
High resolution, low power MR sensor capable of measuring the angle
direction of a magnetic field from a magnet with <0.07>

HMC1501 Datasheet pdf