National Instruments NI USB-6221, NI USB-6229, NI USB-6251, NI USB-6259 LEDs

LEDs

USB-6221/6229/6251/6259 OEM devices have two LEDs that reflect

the device state. The green READY LED indicates whether the device is

powered on and configured as a USB device. The yellow ACTIVE LED

indicates whether there is USB bus activity.

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

circuit to the device. 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 resis tor to t he 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 on. You also can limit this current further by using external

resistors as shown in Figure8.

Figure 8. USB-6221/6229/6251/6259 OEM LEDs

Figure 9 shows how to connect an external READY or ACTIVE LED

circuit to the device.

Figure 9. Schematics of the USB-6221/6229/6251/6259 OEM LEDs

DS1

E3 E2 E1

100 Ω

Internal

3.3 V

External

READY LED

External

ACTIVE LED

External Resistor