Recently i bought a sainsmart arduino kit and it came with a LCD i soldered it to a header and tested it out with the default arduino kit, everything works except the backlight! I tested a bunch of these lcd's (mine being a V1 and the others being a V2) there were about 10 LCD's I tested them all and none of the backlights actually worked except for one, the one that was used by someone else before and i can enable the backlight by connection the K pin to the RW pin and it works fine on that LCD but on the others it refuses to work, it makes me think that there is some sort of configuration for the panel!
the LCD model numbers are 1602A and 1602A v2.0 by sainsmart
How did you wire them and what code did you use ? (post your code and a wiring list or schematic) Specifically, which LiquidCrystal LIBRARY did you use ?
Post a link to the lcd.
nnvt:
... and i can enable the backlight by connection the K pin to the RW pin and it works fine on that LCD but on the others it refuses to work, it makes me think that there is some sort of configuration for the panel!
Please link to the product you bought if you like us to check that for you.
If you have the R/W (meaning Read on HIGH and Write on LOW (/W)) fixed to GND, that will possibly be OK.
You need to power the backlight, not connect it to some Arduino output; the output can not handle the power required.
K means Kathode, Cathode in English, and that goes to GND.
A means Anode, it goes to VCC.
But the current to the backlight needs to be controlled, or else it may burn and form a short.
That's why there needs to be a current limiting resistor.
Some displays have such resistor built in, others do not.
You need to check this before anything else.
82 ohm , 1/2 W gives you the required 4.2V backlight Voltage when connected to +5V
A better way to express this is: "82 ohm , 1/2 W gives you the required 50 mA backlight Current when connected to +5V"
Granted the LCD datasheets frequently list such a 4.2 V parameter but this is probably due to limited skills in 'technical English' rather than it being an actual rating of the backlight LED.
What is actually happening is that the 82 ohm resistance is giving you the required ~50 mA forward current when connected to a +5 volt supply. This in turn means that if you were to then measure the voltage across the backlight LED you would find that it is around 4.2 volts.
I bring this up because many people think that if you were to apply a 4.2 volt supply to this particular backlight LED that it would work properly - which isn't the case.
Once again, what is really happening is that when you limit the current (by whatever means) to the required 50 mA you will measure about 4.2 volts across the LED.
I know this is an older thread but thought i would add to it. here is a pdf link http://oomlout.com/parts/LCDD-01-datasheet.pdf to v2.0 and from my understanding the voltage to the LCD backlight varies dependent on the color of the backlight. My blue backlight takes aprox 3.3v and is very bright with that supply.
... from my understanding the voltage to the LCD backlight varies dependent on the color of the backlight. My blue backlight takes aprox 3.3v and is very bright with that supply.
You too have missed the point. The phrase "the voltage to the backlight" is incorrect. The phrase should have been "the voltage across the backlight" since you are not applying the voltage, you are just measuring what is there.
The (forward) voltage parameter associated with LEDs, and any other diode for that matter, is the resulting voltage that you will measure if the diode is operating at the specified current. It is NOT the voltage that you apply in order for the diode to operate properly. This is essentially what I said in the last sentence of my previous post and nothing has changed in the intervening years.
LEDs are manufactured using different materials in order to get the different colors. The result is different voltages measured across properly operating LEDs of different colors as you have observed.