And if you're running the backlight off the T2's regulator, make sure it's not drawing too much current. Some of the big ones can be pretty power hungry.
Scott Fred Hillhouse wrote: > > [Attachment(s) <#TopText> from Fred Hillhouse included below] > > Hi Steve, > > > PIN Symbol Level Function > 1 VSS - GND(0V) > 2 VDD - Supply Voltage for Logic(+5V) > > 3 V0 - Power supply for LCD <-- A pot between 5V and GND with the wiper > connected to PIN 3 works well. The contrast can be changed as > temperature changes. > > 4 RS H/L H: Data; L: Instruction Code > 5 R/W H/L H: Read; L: Write > 6 E H/L Enable Signal > 7 DB0 H/L <-- not used > 8 DB1 H/L <-- not used > 9 DB2 H/L <-- not used > 10 DB3 H/L <-- not used > 11 DB4 H/L > 12 DB5 H/L > 13 DB6 H/L > 14 DB7 H/L > > ================== > 15 A - Backlight Power (+5V) > 16 K - Backlight Power (0V) > These connections should have a current limiting resistor added in > series. At least on the ones I have used in the past. Actually a pot > here helps to adjust the brightness as needed with a series fixed resistor. > > I added a portion of my schematic. I don't show the VO circuit or the > backlight circuit either. I have a simple pot for VO. I think my pot is > 20K. I am thinking my data sheet actually had a current listed for the > VO pin. > > I usually control the backlight with PWM (contrast too) but it seems a > bit overkill here. > You will want to limit the current to the backlight LEDs. > > The Vf is 4.2 for the Y-G version. > So > 5.0V - 4.2Vf = 0.8V > 0.8V / 0.180A = 5 ohms (rounded 4.44 to 5) > A 5 ohm resistor in series with the backlight LEDs should keep it safe. > > The Vf is 4.0 for the WHITE version. > So, 5.0V - 4.0Vf = 1.0V > 1.0V / 0.030A = 33 ohms > A 5 ohm resistor in series with the backlight LEDs should keep it safe. > > So depending on which model you find, either a 5 or 33 ohm resistor > should keep the backlight in action. > > In you want to dim it further, then a pot in series with your other > resistor can decrease the current (light output) without allowing you to > overdrive the backlight. > > I also added pictures showing my additions to the Tracker2. And there is > one of the LCD in action. > > Best regards, > Fred >
