NI USB-622x/625x/628x OEM User Guide

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Attaching External LEDs

USB-622x/625x/628x OEM devices have two LEDs that reflect the device

state. The green READY LED indicates when the device is powered on and

configured as a USB device. The yellow ACTIVE LED indicates USB bus

activity.

Three connectors on the device allow you to connect an external LED

circuit to the device, as shown in Figure 10. To connect an external READY

LED, use E1 as the positive connection (+3.3 V) and E2 as the negative

connection. To connect an external ACTIVE LED, use E1 as the positive

connection and E3 as the negative connection. E1 is current limited with

a 100

Ω resistor to the 3.3 V internal supply. This configuration limits

the current to approximately 16 mA into a single external LED or

approximately 8 mA each when both LEDs are lit. You also can limit this

current further by using external resistors, also shown in Figure 10.

Figure 10. Schematic for External LED Circuits

E1

External

READY

LED

External

ACTIVE

LED

E2

E3

100

Ω

3.3 V

OEM (On-Board)

E1

E2

E3