Hardware Reference
In-Depth Information
Physical
Type of
parameter
sensor
Notes
Piezo-resistive
Pressure exerted on diaphragm causes changes of resistance
pressure
in attached piezo-resistive transducers. Transducers are usually
sensor
arranged in the form of a four active element bridge which
produces an analogue output voltage. Analogue input port required.
Operator
Switch or
Suitable for providing basic manual on/off control. Available in
push-button*
various formats including conventional toggle, rotary, slide, button,
keyswitch, and foot-operated types. Digital input port required.
Dual in-line
Printed circuit board mounting switch available in single of multiple
(DIL) switch*
forms. Normally only used for selecting options or setting parameters
and unsuitable for frequent use due to small size. Digital input
port required.
Keypad*
More cost-effective than using a number of individual push-button
switches. Also suitable for data entry. Keypads fitted with encoders
require digital input ports. Unencoded keypads are usually configured
as a matrix of rows and columns (e.g. 4
4 in the case of a 16-key
keypad) and will require at least one digital I/O port.
Keyboard*
Provides the ultimate in data entry (including generation of the full set
of ASCII characters). Encoded keyboards are generally easier to use
than unencoded types which are more suitable for memory mapped I/O.
Digital input port required.
Joystick*
Available in both digital and analogue forms. The former type is
generally based on four microswitches (two for each axis) whilst the
latter is based on conventional resistive potentiometers.
Either form is suitable for providing accurate position control
but 'contactless' types are more reliable. Analogue or digital input port
required, as appropriate.
Touch screen
LCD display (requiring a digital output port) with touch
sensitive using finger or stylus and typically requiring a force of
40 g for operation. Contacts have a typical 'on' resistance of between
150
and 1.3 k
and an 'off ' resistance of up to 20 M
. Requires a
digital input port.
Proximity
Microswitch*
Microswitch fitted with actuator mechanism. Requires physical
contact with the target object and small operating force. Also functions
as a limit switch. Digital input port required.
Reed switch*
Reed switch and permanent magnet actuator. Only effective over
short distances. Digital input port required.
Inductive
Target object modifies magnetic field generated by the sensor.
proximity
Only suitable for metals (non-ferrous metals with reduced
switch*
sensitivity). Digital input port required.
Capacitive
Target object modifies electric field generated by the sensor.
proximity*
Suitable for metals, plastics, wood, and some liquids and powders.
switch
Digital input port required.
(
continued
)
