0.91 inch 128 x 32 Dot Matrix 4 Bit OLED USB Voltmeter Current Power Capacity Tester

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Main Features:
Overvoltage, undervoltage remind
Screen flip up / down storage
USB signal lines through without affecting communication
The screen turns off
Group 9-capacity storage
Unit switching capacity
Automatic calibration current zero
Display color: Blue / White
Brand: Jtron
Product weight: 0.013 kg
Package weight: 0.093 kg
Product size (L x W x H): 5.7 x 2 x 1 cm / 2.24 x 0.79 x 0.39 inches
Package size (L x W x H): 12 x 6 x 3 cm / 4.72 x 2.36 x 1.18 inches
Package Contents: 1 x USB Tester

It forbid for being used for inductive load,  eg: The load with motor and fan. 
It can be used for digital products,  eg: mobile phone,  power bank,  USB flash drive,  etc.

When contact the power supply, the screen shows welcome window firstly and then comes into main interface. The first line displays voltage, power and data set. The second line displays current and accumulated capacity.

Current zero calibration function:
Because of the influence of component aging and temperature variation after long-term use, the error may become bigger when it measures small current. So you can keep pressing the button on the back to connect power supply in the no-load terms, until the LED lights. The calibration is accomplished.

Over-voltage and Under-voltage reminding function:

When the voltage is over 5.3V (less than 4.7V), the arrow ˆ (ˇ) will be flashing to remind the voltage is too high (low). When the voltage becomes to 4.7V-5.3V, the arrow will be disappeared.

In the main interface, you can click the button to switch data set one by one. And it provides for storing and checking 0 to 9 totally ten group data set.

Capacity stored function:
When data set is between the 1 to 9 group, the current capacity will be stored after power off. And the stored capacity will be accumulated after power on. When the data set is 0 group, the current capacity will be stored after power off. When power on next time, the stored MAH is blinking displayed .When the new MAH is up to 1 MAH, the stored MAH will be covered, and the values will start over.

 In the main interface, click 2 times the button on the back (the time interval of the two times is within 0.5s), then you can get into data check window and see the capacity of the current data set. In this window, you can click the button to check the next data set, and when you keep pressing the button more than 2s, the current data set will be cleared. And if you click the button two times, it will come back to the main interface.

Counting the capacity and efficiency of the mobile power bank battery:
Ah data * output voltage ÷battery voltage ÷ efficiency = mobile power bank battery Ah (output voltage is typically 5V, the battery voltage is generally based on 3.7V, typically by 85-90% efficiency)

Capacity unit switch function:
In the main interface, keep pressing the button, until the LED lights (time about 2s), loose the button, the capacity between mAh and mWh is switched.

Screen rotation function:
In the main interface, keep pressing the button, until the LED lights and then goes out (time about 4s), loose the button, the screen is rotated and automatically stored for being used next time conveniently.

Shut-down screen function:
In the main interface, keep pressing the button more than 6s, then loose the button, the screen display can be shut-down and come into power saving mode. In the meaning time, the LED is flashing. You can click the button to come back to the main interface.

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