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Thread: Teensy3 + DogM LCD 3.3v Display issue

  1. #1
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    Teensy3 + DogM LCD 3.3v Display issue

    Hello everyone,
    New to this forum . I am in the middle of constructing a flight simulator and would like to incorporate the Navigation Frequency control on the panel as well as interact with NAV controls.
    I am trying to emulate the Nav frequency sketch that Paul Has on his web site. All works well when I fire up Xplane and I can push button the frequency up and down ..not a problem. However, the encoder does not want to increment either way. My real problem is the display (DOG 163). it will not read. I have had this same circuit run from the arduino 2560 and wired up the 163 according to the 5V SPI recommendations. …….run the "hello world" sketch and i get "hello world"..(looks good..no backlight)

    Now when i wire up the Teensy 3 & power it up using 3.3 volts... I wire it with the recommended 3.3 SPI wiring …..that is to say I am now incorporating those two caps you see in the pic. The little .1 microF is jumped across 21 & 22 on the LCD…….and the 1 microF ….is bridging lcd pins 24 and 25 as it goes to 3.3 volts.

    That little resistor you see is the limiting resistor @ 2.2 ohms (even though I do not have the LCD(backlight module) in this setup. (had a 68 ohm with 5v & it was ok)

    I am picking up the 3.3v supply from that big red wire next to AGND……..and GND off of AGND.

    doing something wrong as I can not even get the "hello" to show up…don't mind the blink sketch in the pic…i use it to make sure the board is healthy




    Click image for larger version. 

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  2. #2
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    Update : I have tried all combo's of capacitors to voltage boost the Dog163 LCD with no luck..

    Has anyone successfully powered up a Dog 3.3 v lcd with Teensy3 ?????

    If not I may have to "cut the Pad" and fire up the teensy with a 5 volt external power supply and dump the USB power...don't want to fry my second Teensy however

  3. #3
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    Hey Paul, I did follow all that grey encoder business on the other forum so I know you got that going today..Btw...I have my alps encoder registering pretty well on the Basic sketch with the teensy3.........where you able to fire up your Dog LCD with Teensy 3 yet ....don't know why it wont talk..

  4. #4
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    I came across this code for the DOG LCD operating at 3.3 volts. Does anybody know if these displays are default at 5v but you need this code to tell the lcd its operating at 3.3 volts

    Example 3 When operating at 3.3V we have to supply a value for each of the arguments

    myDisplay.begin(DOG_LCD_M162,0x30,DOG_LCD_VCC_3V3) ;

  5. #5
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    Update : I have the LCD reading with 3.3 volts with code on last post. Very ,,Very faint characters. Below is how i hook up to the teensy3

    Click image for larger version. 

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  6. #6
    https://www.sparkfun.com/products/10968

    No need to cut any pads. This 5v step-up breakout works great for me.

  7. #7
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    so the 3.3v from the teensy3 gets intercepted by the step up and in turn supplies low ripple clean 5volts to the dog163 LCD....that sounds like a quick solution..it is just a shame the teensy can do it on it own

  8. #8
    Quote Originally Posted by Maxx1 View Post
    so the 3.3v from the teensy3 gets intercepted by the step up and in turn supplies low ripple clean 5volts to the dog163 LCD....
    I'm not sure what you mean by intercepted, but as long as the LCD doesn't need more than 100 mA, you can connect the step-up to the teensy 3.3V pin, and then connect the LCD board to the step-up 5V pin. As long as the LCD can still handle 3.3V logic, you should be good to go.

  9. #9
    Senior Member PaulStoffregen's Avatar
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    Ok, I found my DogM test board. I put a Teensy3 in the socket and ran the library's HelloWorld example. It seems to work fine. Here's a couple quick photos.

    Click image for larger version. 

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    (click for large image)
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    In this test, the LCD is powered by 5 volts. The LCD is able to accept Teensy3's 3.3 volt signals. Since all 4 are unidirectional from Teensy3 to the LCD, there's no danger of damage to Teensy3 with the LCD running from 5 volts.

    Hope this helps?

  10. #10
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    Ok Paul it does help..so I take it you have an external 5v going to VDD ,,,,,,,,,SI,,,,CLK,,,,RS,,,,,CSB.....all safe from the teensy....(D5,,,D4,,,D3,,,D2,,,D1,,D0,,,E,,,all to 3.3voltsTeensy)....No Caps
    and daperl.....suggests the 5 volt step up which sound good as well.
    Mike

  11. #11
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    one more question.what was your current limiting resistor value

  12. #12
    Senior Member PaulStoffregen's Avatar
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    100 ohms (brown, black, brown, gold)

  13. #13
    Sorry if I confused you. I need the 5V step-up because I'm running the teensy3 off of a 3.7V battery, but if you're running off of USB power you can get your 5V from the teensy3 VUSB pin. So, when running off of USB power, you don't need the step-up.

  14. #14
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    Paul,Daperl,

    We have success...that little circuit to the lower left is a voltage reg cicuit utilizing 100R1 & 300R2 ohm resistors,,,yielding 5v

    Click image for larger version. 

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