Go Down

Topic: Max. Current LCD with I2C backpack (Read 567 times) previous topic - next topic

Hltlnd112

Yesterday i learned how to work with an lcd 1602(with I2C backpack), but i am afraid that if i have an project with an LCD, i cant really connect more stuff to my uno board (max. 200 mA) due to too much current.
How much current is there really drawn with the backlight on?
I searched (probably not good enough), but cant find a usefull answer.

david_prentice

The backpack has a 2-pin header with a jumper.
Remove the jumper.   Measure the current with a DMM.

Normally a 16x2 backlight would take 20mA - 50mA.   Anything more and it means the backlight needs a series resistor.    Some modules just have 0R resistors mounted on the pcb.

Either replace the 0R with a sensible value SMD resistor e.g. 47R
Or connect a wire-ended resistor across the 2-pin header.

David.

Hltlnd112

Thanks
But do you (maybe) know how much current the entire lcd draws?
Thanks in advance.

david_prentice

Not really.   You can measure it yourself.   

I would guess 2-10mA for the LCD and 20-50mA for the backlight.

David.

bperrybap

The current can vary substantially.
I have several 16x2 LCDs that have backlights that draw under 3ma and I have some 20x4 that draw over 200ma.
There can also be a significant difference between the positive vs the negative type LCDs.
i.e. the ones that have black pixels on a green/yellow background vs the ones that have white pixels on a blue background.
The 2-10ma range is about right for the LCD chip itself, I've seen about 15ma on quite a few, but the current varies depending on the state. i.e if you turn the pixels off, the base level current of the chip drops significantly.

The only want to know, how much current your particular LCD draws will be to actually measure it.

--- bill

david_prentice

@Bill,

Does your 200mA 20x4 have 0R resistor in R8 / R7?
100R is quite common.    Meaning that you get about 20mA LED current with 5V on VA, VK

I just assume that the LEDs have some internal resistance e.g. 10R would give about 200mA @ 5V
If you use PWM you could vary the average current but I doubt if any backlights are specified to run with a continuous 200mA.

An internal 10R resistance would give you a sensible backlight current @ 3.3V.

Ebay vendors don't care what they sell.

David.

bperrybap

Well, I can't find my high current backlight LCD. I did measure the current on 5 different LCDs with i2c backpacks.
One 20x4 used 25ma for the backlight, the 4 others (16x2) which were different types positive and negative displays used between 15ma and 20ma.
The device (LCD and backpack - some of which have pullups) with the backlight off was 1.7ma to 7.5ma

The ballpark for the 16x2 devices with the backlight on was around 20ma.

Hltlnd112,
You should actually measure the current for you device.
If you don't have a meter, then go buy one they are not expensive; harbor freight gives them away all the time.

--- bill

Hltlnd112

I measured it on the 5v jumper cable and it turned out to be 20 mA

david_prentice

That confirms that your LCD is taking a sensible current.

You have no worries about power supply or current consumption.
I guess that your LCD module has 100R SMD resistor in R7 / R8 position.   (marked 101)

David.

Perehama

i cant really connect more stuff to my uno board (max. 200 mA) due to too much current.
This only applies to ports on the UNO that are sourcing or sinking current, and up to 20mA per port (40mA max.). For example, if you connect up to 8 ports on your UNO to a ULN2803, you can sink 500mA per channel, up to 2.5A for all 8 channels. (Refer to the manufacturer's spec sheet for actual product specifications.)
F=C/V=(A*s)/V=J/V^2=(W*s)/V^2=(N*m)/V^2=C^2/J=C^2/(N*m)=(s^2*C^2)/(m^2*Kg)=s/Ω=1/(Ω*Hz)=s^2/H

you have read boarch and understand to porton thẻ undo lcd, when you knowlege , you will receive project. thank all share. dang ky bong88

Go Up