I got out a Sparkfun white on black 16x2 that I have had for a few years now and was testing some things on a circuit I'm working with. Apparently it's a GDM1602K according to Sparkfun's website, unless they changed the model since I bought it.
The spec sheet suggests 140mA current for the backlight.
I'm confused because my entire project measured at power supply to Vin is only 35mA. Everything is running off of a 5V 2A buck stepdown module, and the Arduino is powered through the Vin pin. I measured the volatage at the A-K pins on the LCD and it was at 5.0-5.1V, and the current there measured about 16-17mA, so the Arduino and everything else is using about 18mA. There are 3 DS18B20 temp sensors and an SD micro breakout module connected as well.
Thinking my multimeter was inaccurate, I made a simple test circuit with a 220 ohm resistor (measured 219ohm) using the same power supply and got 22.85 mA. V=IR suggests 22.7, so I'm thinking my DMM is accurate enough.
I'm suspecting the datasheet is wrong, or this is not exactly the same model? The backlight is quite bright.
Is this a possibility or am I missing something?
To be clear, I do not have a current limiting resistor on the backlight. I measured the project current by connecting the power from positive output of the 5V power supply to my red lead, then my black lead to the point where the power connects to the circuit. DMM is an Extech 355 and I had my leads on the mA and COM sockets, measuring mA DC.