User Manual

RedLab 1208LS User's Guide Functional Details
20
Figure9. Digital connection Port A0 detecting the state of a switch
+5V+GND
Port A0
Figure 10. Schematic showing switch detection by digital channel Port A0
For more information on digital signal connections
For more information on digital signal connections and digital I/O techniques, refer to the Guide to Signal
Connections (available on our web site at www.mccdaq.com/signals/signals.pdf).
Power terminals
The PC +5 V connection (pin 30) is on the bottom screw terminal of the RedLab 1208LS. Refer to the pinout
diagrams on page 16 for the location of this pin. This terminal draws power from the USB connector. The +5 V
screw terminal is a 5 volt output that is supplied by the host computer.
Caution! The +5V terminal is an output. Do not connect to an external power supply or you may damage
the RedLab 1208LS and possibly the computer.
The maximum total output current that can be drawn from all RedLab 1208LS connections (power, analog and
digital outputs) is 500 mA. This maximum applies to most personal computers and self-powered USB hubs.
Bus-powered hubs and notebook computers may limit the maximum available output current to 100 mA.
Just connecting the RedLab 1208LS to your computer draws 20 mA of current from the USB +5 V supply.
Once you start running applications with the RedLab 1208LS, each DIO bit can draw up to 2.5 mA, and each
analog output can draw 30 mA. The maximum amount of +5 V current available for experimental use, over and
above that required by the RedLab 1208LS, is the difference between the total current requirement of the USB
device (based on the application), and the allowed current draw of the PC platform (500 mA for desktop PCs
and self-powered hubs, or 100 mA for bus-powered hubs and notebook computers).
Pin 40
GND
Pin 30
PC +5 V)
Pin 21
Port A0