I'm a programmer not an EE so I'm in need of a sanity check before I pursue my idea to completion.
Basically I want to have a software switch to an I2C LCD display (the dfrobot one) to turn it on and off by powering it from an Arduino pin and from what I can see I should be able to do it.
The LCD data sheet is not clear on it's power consumption however I found that it consumes a measured 17.5mA operating at 5v and the arduino pins (from the data sheet) have a max of 40mA.
17.5mA is even less than some LED's configurations run at.
I know that I could put it through a transistor but don't want to if it's not necessary.
The rest of the circuit that the arduino is controlling consists of I2C and Shift registers so there is no other significant power consumption to speak of.
So it should be good from what I can see but I cannot trust that i'm not missing something fundamental so would be happy if someone could validate my thinking on this.
I would think it's ok. One thing you should consider though, is the voltage sag when a load is applied to a digital pin. As far as I know, they are only guaranteed to output 5V without an appreciable load. 17ma might cause it to drop somewhat (perfectly normal and within specs), and this might be below the minimum supply for the lcd module to function properly.
I ran the arduino off 4 partially depleted AA's to see how it performed and due to the voltage drop the current through the display dropped by 0.5mA and it got a little dimmer but still seemed to be going strong.
The rest of the project should run on a supply down to 3.8v without issue but probably not the LCD.
As an alternative, use a transistor to power the LCD.
This is what I ended up doing for exactly the reasons stated. I was concerned about hitting my current out limit on the Arduino but I need the Arduino to turn the LCD on. I used a TIP120 to power the LCD straight from the 5V pin.
