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Nextion, TJC, Character LCD current consumption

Nextion, TJC, Character LCD current consumption

When using Nextion LCD, the first question I get is 'What is the current consumption?' I do not know. I did not even know the name of Nextion LCD until recently.
CEC Firmware Users continued to talk about Nextion LCD, so I got to know Nextion LCD. I even confused TJC LCD and Nextion LCD.
Instruments used in this document are not guaranteed to be accurate.



1.Experimental conditions
 Nextion LCD : 2.4", 3.2"
 TJC LCD : 2.8"
 Character LCD (Blue backlight) : 16x02, 20x04

2.TJC LCD 2.8"
2.1 Current consoumption for Backlight adjust
LCD Setup Screen
Backclight : 100%


Current Consumption : 86mA


Backlight : 50%


Current Consumption : 47mA



Backlight : 10%


Current Consumption : 29mA



2.2 Brightness measurement at Main VFO Screen
Backlight : 100%


Current Consumption : 88mA



Backlight : 50%


Current Consumption : 47~48mA


3.Nextion LCD 2.4"
3.1 Backlight adjust
Backlight : 100%


Current Consumption : 89mA


Backlight : 50%


Current Consumption : 56mA


Backlight : 10%


Current Consumption : 30mA


3.2 Main VFO Screen
Backlight : 100%


Current Consumption : 90mA


Backlight : 50%


Current Consumption : 57mA


4.Nextion 3.2"
4.1 Backlight adjust
Backlight : 100%


Current Consumption : 124mA


Backlight : 50%


Current Consumption : 75mA


Backlight : 10%


Current Consumption : 37mA


4.2 Main VFO
Backlight : 100%


Current Consumption : 125mA


Backlight : 50%


Current Consumption : 76mA


5.Character LCD 16x02, 20x04
5.1 16x02 LCD Green Back Light


Current Consumption : 21mA


5.2 16x02 LCD blue backlight


Current Consumption : 19mA


5.3 20x04 LCD bluebacklight


Current Consumption : 57mA


6.Character LCD 16x02, 20x04 with I2C
16x02


Current Consumption : 24mA


20x04 LCD


Current Consumption : 59mA


7.Conclusion of experiment
LCD100%50%10%
Character 16x02 I2C blue backlight (parallel)24(19)
Character 20x04 I2C blue backlight (parallel)59(57)
TJC 2.8"864730
Nextion 2.4"895630
Nextion 3.2"1247537

The results are shown in the table above.
Most of the common 5Volt power supplies built into the transceiver support 250mA ~ 1A, so there is no big problem to use. I recommend that you attach a heatsink to the regulator (EX: 7805), a 5Volt power supply built into the transceiver.
As you can see from the table above, you can further reduce current usage by slightly reducing the brightness.

But it has a problem !!!.

If you adjust the brightness of the LCD, noise will occur. It may be a common problem in most LCDs that adjust brightness with frequency control.
Perhaps you can come up with a variety of ways to reduce noise, There may be a way to shield the LCD or make some modifications.

If you want to change the default brightness of the LCD in hardware, it is recommended to limit the current supplied.

8.Using resistors to adjust brightness
This method is used when you want to use your radio as Portable and want to reduce the current consumption a little more.
Insert a resistor in the middle of the +(5volt) line,  The resistance can be between 20 ohms and 100 ohms. You can adjust the desired brightness without any noise.
important : 
1. If you use this method, you will no longer be able to update using the SD card.
2. If the resistor value is too high, the LCD will not operate normally.



In case Nextion 2.4",
It will probably be applied to other size LCDs as well. Below is a calculated value, which will cause some errors in actual use.

Direct Connect (without any resistor) : 89ma
20ohm : 60~70ma
50ohm : 40~50ma
80~100ohm : 29~33ma

Most resistors have a capacity of 1/4W. That's why I built two 100-ohm resistors in parallel to make 50 ohms as shown below.
If you use a slightly larger LCD, I recommend using three 100~200ohm ohm resistors in parallel.

Below is a 50 ohm connection to the TJC LCD for experiments


It is a screen with current limit of 50 ohm.


Current Consumption : 43mA



9.My DIY
Too bright the LCD tires the eyes, so I decided to reduce the brightness.

resistor 100ohm * 2
(It is recommended to connect three 150ohm resistors in parallel)

slide switch : 1


Two 100 ohm resistors were connected in parallel to make 50 ohms.
This is the end. It's too simple, right?




Applied to LCD


Switch On : direct connection (without resistor)


Swtich Off : 50ohm Resistor

Current consumption is reduced to 1/2, I probably need to increase the resistance a little more.

If you limit the current to the LCD with a resistor, you can not update the firmware using the SD card as shown below.


Below, you can see the normal operation when the switch is turned on.


Thank you for reading.
Ian KD8CEC

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