Appendix B:
Connection of an External 5 Volt Supply
When using the KE24 in an application that does not require
connection to a PC (such as an RS-232 keypad interface), an
external 5 volt power supply must be used. The KE24 has a
connection point that is dedicated for this purpose.
Two solder points are supplied for attaching external wires or a
connector to the KE24 to supply the 5 volts.
Special care must be taken to assure the proper polarity of the
voltage. The supply must be within 4.75 to 5.25 volts DC.
Note:
Reverse connection of the supply voltage will permanently
damage the unit. Use 5 volt source only. Do not attempt this
connection if you are uncertain of your power supply voltage or
polarity.
NEVER
attach a KE24 that is powered from an external source
to a PC, as this may damage the KE24, the computer, and/or your
supply.
26
Ground
Connection
+5 Volt
Connection
Interfacing to the KE24 I/O Header
The 52 pin header on the KE24 consists of 24 I/O points with
ground connections on either end. Each pin of the dual row
header is connected in parallel with its adjacent pin. Therefore,
each I/O signal is available on two different pins.
Each of the 24 I/O pins may be configured by the KE24Load
program. Pins may be independently configured to be either Rows
or Columns in a matrix scanning application, or discrete inputs.
Activation of an input in a matrix mode requires that a row and
column be shorted together to produce a keystroke. Discrete
inputs are activated by shorting the desired input to the ground
signal located on either end of the dual row header.
Figure 1.1 demonstrates how to activate an input that has been
programmed to be a discrete input. Although a switch is shown in
this diagram, other devices may be used in this mode to
5
Figure 1.1
Inputs used in discrete mode
must be shorted to ground to
activate them. Switches, key-
pads, or other electronic de-
vices that “sink” at least 1 ma
of current may be used.
