The R2D2 Expander increases I/O (Input/Output) and
electrical immunity for an Interrogator. It serves as
a hardware firewall for external devices connected to
your RFID reader.
Power
is supplied to the R2D2 Expander by means of an
external power supply (24volts @ 3A).
The photocoupler separates the internal
circuitry of the reader from the external devices that
it is monitoring or controlling.
The 24V input to the R2D2 Expander provides
power to the external side of the photocoupler.
The external power supply my also provide power
to the devices that are connected to it.
Figure
1
shows a typical configuration using the R2D2
expander.
A closer look at the R2D2 Expander as shown in the block diagram (Figure
2
) reveals that the optical isolation block has
a 5volt connection from the GPIO port of the reader or
host that it is connected to.
Using the power from the equipment that is
being protected isolates the power from external
devices connected to it.
The output signals are optically isolated then
connected to a driver block that can control six
devices providing drive capability up to 50v @ 500mA
each. The 24 volt connection from the power supply to
the optical isolation blocks is detailed in (Figure
3
).
Figure
2
Block Diagram
The
Light Emitting Diode (LED) and the photo transistors
are connected to either +5V from the reader or +24V
from the external power supply.
If the signal being isolated is an input then
the photo transistor is connected to +5V and the LED
is turned on by the external device closing a switch
that providing a forward bias current.
For output signals the LED is forward biased
when the TTL signal from the reader is cleared or set
to a value of 0.
Figure
3
Optical Isolation Blocks
This
section provides a general description of how to
connect the external input and output devices to the
R2D2 expander.
Output devices usually require power to turn them on.
Light stacks for example (Figure
4
) connect the individual lights to the outputs
pins on the R2D2 Expander which provides a current
path to ground and thereby a power connection that is
shared by all the lights in the stack.
Other devices such as solenoids that control
diverters or motor on/off control may be connected in
a similar fashion but the user should follow the
manufactures guidelines when connecting it to the R2D2
Expander.
Figure
4
Light Stack Connection
Input
devices such as motion sensors (Figure
5
) have a relay or other type of internal switch
which closes or opens upon an occurrence of an event.
When the switch is closed the LED in the
photocoupler is turned on thereby causing current to
flow in the phototransistor which changes the state of
the input pin on the reader.
Figure
5
Motion Sensor Connection
Figure
6
Output Connections
Figure
7
Input Connections
Figure
8
GPIO Connections
Figure
9
Power Connection
|
Output
Sustaining Voltage
|
-0.5
~ 50
|
Volts
|
|
Output
Current (Max)
|
500
|
mA
|
|
Input
Voltage (Max)
|
24
|
Volts
|
|
Input
Current (Max)
|
1000
|
mA
|
|
Power
Dissipation
|
1.47
|
Watts
|
|
Operating
Temperature
|
-40
~85
|
C
|
Table
1
|
GPIO
|
General Purpose Input and Output
|
|
TTL
|
Transistor Transistor Logic
|
|
RFID
|
Radio Frequency Identification
|
|
Optical
Isolation
|
Isolation between two electrical circuits using an
Light Emitting Diode and Photo Transistor
|
|
Photo-Eye
|
A device that projects a beam that is reflected back
to a sensor. When this beam is broken a switch
(or relay) internal to the device will open or
close depending upon how it is configured or
connected
|
|
Motion
Sensor
|
A device that uses ultra sonic signals to detect
motion within it’s field of view. When motion
is detected the device will open or close a
relay or switch. Typically a motion sensor will
hold the signal for a configurable amount of
time
|
|
Light
Stack
|
A column of lights that are used to give a visual
indication to a user of some system
|
|
Solenoid
|
An electro-mechanical device that will move in or out
of a magnetic field to express mechanical work
based on a electronic signal that is sent to it
|
|
