15
LOGIC OUTPUTS
The SPM723 provides eight logic outputs on a rear panel 9-pin Subminiature D (male) connector. Logic Outputs can be used to control
external circuits such as relays, indicators, etc. (see diagrams below). However, the SPM723 Logic Outputs are most often used to provide
simultaneous audio & video source selection, by controlling an external video switching device which has logic inputs or other means of
control via external contact-closures (logic outputs). Multiple Logic Outputs may be combined (wired in parallel) to control a single circuit.
The SPM723 Logic Outputs are ‘open collector’ outputs. Each Logic Output is an NPN transistor with the collector being the output and the
emitter being ground (see diagram below). When a Logic Output is turned on, the transistor provides a path for DC current to flow. The
Logic Outputs do not provide any voltage or current. They act only as switches (with a common ground return). To activate external
relays, an external power supply must be used (see diagram below). The Logic Output transistors are rated up to a maximum of 24 VDC
and 50 mA per output (24 volt relay coils maximum). However, +12 Volts DC is sufficient power for most applications. When using the
Logic Outputs to control relays, protection diodes must be used to suppress high voltage transients that are generated when the relays turn
off (see diagram below). Any of the 1N4004 family of diodes (1N4001, 1N4002, 1N4003, 1N4004, 1N4005, 1N4006, 1N4007, or
equivalent) will provide proper protection. When a Logic Output goes on, the associated relay may be wired to perform on, off, or ’A/B’
switching functions. To use logic ‘on’ to turn on (or activate) a device, wire across the ‘normally open’ relay contacts, in series with the
device (or control voltage source). To use logic ‘on’ to select between ‘A’ or ‘B’ signals (inputs or outputs), wire one signal to the ‘normally
closed’ relay terminal and the other signal to the ‘normally open’ relay terminal, with the common relay terminal providing the feed (input or
output).
logic out
pin number
Logic Out 1
Logic Out 2
Logic Out 3
Logic Out 4
Logic Out 5
pin #1
pin #2
pin #3
pin #4
pin #5
pin #6
pin #7
pin #8
pin #9
Logic Out 6
Logic Out 7
Logic Out 8
ground
9-pin cable-end
5
9 8
7 6
1
2
3
4
logic
outputs
1
2
3
4
5
6
7
8
9
Logic Output Controlling Relay
+12 Volts DC
Power Supply
−
+
Logic Output #1
1N4004
Diode
Contacts
Coil
common
normally closed
normally open
SPM723
Pin #1
Pin #9
12V Relay
Logic Output Controlling LED Indicator
SPM723
+12 Volts DC
Power Supply
−
+
Logic Output #1
Pin #1
Pin #9
LED
Indicator Panel
1.2k ohms