# Character (HD44780 based) LCD backlight is always on

I have a Solomon LM1112SYL 4x16 LCD. The display has 16 pins and the datasheet (http://www.allelectronics.com/mas_assets/spec/LCD-108.pdf) shows that pins 15 & 16 are for the backlight power supply. When I power up the LCD without having any connections made to pins 15 & 16, the backlight is on. I would like to have the ability to dim or power off the backlight.

I see that on the back of the module it is has a block silk-screened on it which appears to be for the backlight.

    VDD/VSS JI,KI
15K/16A JK
15A/16K JA


I believe what this information is telling me is that JI is VDD and KI is VSS. If JK pads are shorted to the pads then pin 15 will be the cathode and pin 16 will be the anode to the backlight LEDs. If JA pads are shorted to the pads then pin 15 will be the anode and pin 16 will be the cathode to the backlight LEDs.

I have not followed the traces yet to confirm this. Does anyone know if my assumption is correct? I have not it tried yet as I don't want to ruin anything but I may give it a go once I trace the connections and make certain there will be no ill affects.

## Update

Thanks Fido UK, for pointing out what should have been obvious but escaped me for a time. For some reason I was thinking that there was a via or something where those blobs of solder were. I took my solder wick out and unsoldered the blobs and found jumper pads underneath. Works great now.

• So what stops you from checking your theory with a multimeter? Is it quicker to post a question and wait for someone to take a guess as to how the PCB is routed? – Armandas Dec 9 '12 at 22:08