11-4 Digital I/O, Analog Outputs, and External Feedback
CAUTION Do not exceed +33V maximum voltage on pin 5 of the digital I/O port, and
do not use any output line to sink >500mA. Exceeding these limits may
cause damage to the instrument that is not covered by the warranty.
An externally powered relay connected to the digital output port is shown in Figure 11-3.
Other externally powered devices can be similarly connected by replacing the relay with the
device. When the output line is set LO (0V), the output transistor sinks current through the exter-
nal device. In the HI state, the output transistor is off (transistor switch open). This interrupts
current flow through the external device.
+5V
1kΩ
Pull Up Resistor
Pin 9 - Digital Ground
Pin 1 - Digital Output #1
Pin 5 - External Voltage Flyback Connection
Digital Output #1
Flyback Diode
To other three
digital outputs
Relay
Coil
Relay
Coil
(+)
(+)
(-)
(-)
External Power
(+5V to +33V)
External Power
(+5V to +33V)
Model 6514
Transistor Switch
Flyback
Diode
Equivalent Circuit
Figure 11-3
Controlling externally
owered relays
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