Campbell Scientific CR200/CR200X-series Dataloggers - Manual (Page 61)

Section 5. Measurement and Control
Peripherals
Peripheral devices expand the CR200(X) input / output capacity. Classes of
peripherals are discussed below according to use.
Read More! For complete information on available measurement and control
peripherals, go to APPENDIX. Sensors and Peripherals (Appendix p. 28),
www.campbellsci.com , or contact a Campbell Scientific applications engineer.
5.1 Control Output
Controlling power to an external device is a common function of the CR200(X).
On-board control terminals are available for binary (on / off) control.
Many devices are conveniently controlled with the SW Battery (Switched 12
Volt) terminal on the CR200(X). Applications requiring more control channels
or greater power sourcing capacity may be satisfied by using control ports C1 –
C2 in conjunction with single-channel switching relays.
5.1.1 Binary Control
5.1.1.1 Digital I/O Ports
Each of 2 digital I/O ports (C1 - C2) can be configured as an output port and set
low (0 V) or high (5 V) using the PortSet () or WriteIO () instructions. A digital
I/O port is normally used to operate an external relay driver circuit because the
port itself has limited drive capacity. Drive capacity is determined by the 5V
supply and a 330 ohm output resistance. It is expressed as:
Vo = 4.9V - (330 ohms) * Io
Where Vo is the drive limit, and Io is the current required by the external
device. FIGURE. Control Port Current Sourcing (p. 50) plots the relationship.
49