View Full Version : 16x2 LCD supply and backlight driven from Pic pin ??

- 3rd August 2014, 11:22

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


- 6th August 2014, 06:16
Something like this (http://www.picbasic.co.uk/forum/showthread.php?t=794) ?

- 7th August 2014, 09:12
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.

- 7th August 2014, 10:29
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

- 7th August 2014, 10:31
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

- 7th August 2014, 10:50
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.

- 24th September 2014, 21:32
Thank you all

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

- 25th September 2014, 15:53
Any chance you could post a curcuit diagram, for us hardware dweebs.


- 26th September 2014, 19:00
Any chance you could post a curcuit diagram, for us hardware dweebs.



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

- 26th September 2014, 23:58
Now you made me look up MOSFETs to refresh my memory. This guy has a nice explanation:


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


- 27th September 2014, 08:06
Good Find Robert ...

Very useful !