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RE: [tracker2] Tracker2 with LCD display

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  • Fred Hillhouse
    Hi Steve, PIN Symbol Level Function 1 VSS - GND(0V) 2 VDD - Supply Voltage for Logic(+5V) 3 V0 - Power supply for LCD
    Message 1 of 34 , Sep 17, 2009
     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
  • JohnD
    ... Power up sequence? What Power up sequence? Ohhhhhhhhh, you mean *that* power up sequence. Fred tells me the following in an email The LCD has a
    Message 34 of 34 , Jun 7, 2010
      > - display outputs gibberish characters on lines 1/3 when T2 writes to it. But I never see gibberish on lines 2/4
      >


      Power up sequence? What Power up sequence? Ohhhhhhhhh, you mean *that* power up sequence.

      Fred tells me the following in an email "The LCD has a particular startup sequence and this will only be done at the T2 startup."

      Whereas, I took the WIKI quite literally "No configuration is necessary. The standard Tracker2 firmware will begin using the display automatically. "

      So, I just plugged it in, hot. What a newbie mistake!

      > -I put an SPST switch on +5v input (pin 15 on the mono8) and
      > here's the really weird part. When I turn on the switch, the display and the backlight LEDs come on. When I turn off the switch, the LEDS remain on, but dim down a bit.
      >
      >
      Bad switch - still delivering +3.9V power in the OFF position
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