16x2 LCD supply and backlight driven from Pic pin ??


Closed Thread
Results 1 to 11 of 11
  1. #1
    Join Date
    May 2012
    Location
    Merseyside, UK
    Posts
    237

    Default 16x2 LCD supply and backlight driven from Pic pin ??

    Hello

    Thank you for the quick read….

    Is it deemed correct to drive a 16x20 LCD and back light direct from a single output Pin.

    Don't worry, when I say direct I "DO" mean via a Transistor or Darlington buffer….

    I am using an interrupt routine which will put the PIC to sleep…but the LCD is hung on the supply rails, The LCD will stay on, so was thinking if I hang it on a spare output port it can be shutdown before the PIC goes to sleep.

    Or is there a more elegant way of doing it??

    Thank you again

    Andy

  2. #2
    Join Date
    Dec 2008
    Location
    Ploiesti, ROMANIA
    Posts
    575


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Something like this ?

  3. #3
    Join Date
    May 2012
    Location
    Merseyside, UK
    Posts
    237


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Close.... I have seen this.

    What I am after is whether I can or can't use the PIC pin to turn the 5v supply to the LCD (Vss / Vee) on and off.

    Thank you.

  4. #4
    Join Date
    Sep 2009
    Posts
    737


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Just connect display VDD to any output pin of pic.
    To turn off display set to 0 all data and control pins for display, then set Vdd to 0. If output pins going to display isn't cleared, and Vdd is set to 0, that will probably damage LCD.
    To power up display:
    1. set Vdd pin to 1
    2. FLAGS=0 'Clear PBP flags to enable LCD Init on first LCOUT command
    3. PAUSE 1000 'Wait for display to turn on
    4. LCDOUT $FE,1 'Clear and Init LCD

  5. #5
    Join Date
    May 2013
    Location
    australia
    Posts
    2,383


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    most pic chips can sink or source 20ma on each I/O pin subject to a maximum package limit .
    some questions
    1 what pic chip are you using ? and what other load('s) does it have
    2 whats the max current requirement of the display ?
    3 whats the minimum vcc for the display to function correctly ( there will be some volts lost in this process)
    4 why not use a mosfet

  6. #6
    Join Date
    Sep 2009
    Posts
    737


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    2. 16x2 LCD usually need only 2-3mA for driving LCD without backlight. So it's not problem to drive LCD directly from pic.
    3. Most LCD operate from 4.5 to 5.5V.
    4. For most standard 16x2 LCD there is no need. But if you want, you could.

  7. #7
    Join Date
    May 2012
    Location
    Merseyside, UK
    Posts
    237


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Thank you all

    Bit the bullet and used a FET 2n7000 I think.

  8. #8


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Any chance you could post a curcuit diagram, for us hardware dweebs.

    George

  9. #9
    Join Date
    May 2012
    Location
    Merseyside, UK
    Posts
    237


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Quote Originally Posted by towlerg View Post
    Any chance you could post a curcuit diagram, for us hardware dweebs.

    George
    Name:  photo.JPG
Views: 777
Size:  562.6 KB

    Looks just like the above ….. It was a 2N7000 (Standard Circuit) Even remembered the pulldown !

  10. #10
    Join Date
    Jan 2005
    Location
    Montreal, Quebec, Canada
    Posts
    2,588


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Now you made me look up MOSFETs to refresh my memory. This guy has a nice explanation:

    http://www.talkingelectronics.com/pr...ET/MOSFET.html

    Lots of DO's and DON'Ts at the bottom; I knew practically none of them.

    Robert

  11. #11
    Join Date
    May 2012
    Location
    Merseyside, UK
    Posts
    237


    Did you find this post helpful? Yes | No

    Default Re: 16x2 LCD supply and backlight driven from Pic pin ??

    Good Find Robert ...

    Very useful !

Similar Threads

  1. Electroluminescent LCD backlight
    By Demon in forum Schematics
    Replies: 17
    Last Post: - 9th May 2011, 09:45
  2. LCD 16x2 HD44780U on 3V pic Directly?
    By ngeronikolos in forum mel PIC BASIC Pro
    Replies: 5
    Last Post: - 28th April 2008, 16:04
  3. Lcd Backlight
    By jcleaver in forum mel PIC BASIC Pro
    Replies: 2
    Last Post: - 10th April 2007, 06:00
  4. 16x2 lcd with blue backlight selling
    By macx75 in forum Adverts
    Replies: 5
    Last Post: - 8th May 2006, 08:12
  5. Easy LCD BackLight
    By Melanie in forum Schematics
    Replies: 0
    Last Post: - 17th October 2004, 14:18

Members who have read this thread : 2

You do not have permission to view the list of names.

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts