Huawei EM820W 11LEDWWAN signal, Pins Name Description Additional Direction to Module, Ledwwan

HUAWEI EM820W HSPA+ PC Embedded Module
Hardware Guide				Description of the Application Interfaces
	Table 3-11LED_WWAN signal
	Pins	Name	Description		Additional	Direction to
					Description	Module
	42	LED_WWAN	Active-low LED signal		L: Light on	Output
			indicating the status of		H: Light off
			the module.

This signal is used to display the state of WWAN. The reference circuit diagram is shown in the following figure.

Figure 3-4LED_WWAN# signal reference circuit diagram

Normally, when the HUAWEI module is enabled, the LED is on, and when disabled, the LED is off. The wink mode of the LED can be customized according to the requirement of the client.

For resistance of R placed on PC, choose the value that satisfies the following equation:

IF*R+VF+IF*100 =VCC

VF: Forward Voltage

IF: Forward current

Take the LED 19-213/GVC-AMNB/3T as an example (its manufacturer is Everlight Electronics., Ltd. and the website is http://www.everlight.com). Figure 3-5 shows its IF-VFcurves. If VCC is 3.3 V and the desired current through the LED IF is 3 mA, then the voltage of the LED VF is 1.5 V. According to IF-VFcurves, the corresponding value for resistance of R is (3.3 - 0.003 x 100 - 1.5) / 0.003 = 500 Ω.

The brightness of the LED depends on the current value, and for most of the indicator lights the current between 2 mA to 5 mA is adequate.

Issue 01 (2010-12-31)	Huawei Proprietary and Confidential	15
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