adopting a 5v LCD for 3.3v

lord loh.

Member

• Jun 6, 2008

• #1

I have got a 5v LCD module that i need to adopt for 3.3v of operation. Could anyone suggest me anything?

I have a board which has a 3.3v IC so I have to keep my supply voltage 3.3v The LCD goes blank at this voltage. One way is that I put a separate voltage source for the LCD. But this shall mean 3.3v of IO signals. Is this okay? Do I need to place a level shifter on all IO pins?

Please don't ask me purchase a 3.3v module I cant find one in the local store and shall not be allowed to order one from Digikey or some such online store

Thanks in advance.

 

U

Ubergeek63

Well-Known Member

• Jun 6, 2008

• #2

if the module has TTL instead of CMOS you can run it at 5V. If the logic will run at 3V just run the VLCD at 5V. Otherwise put an HCT buffer between the two and run the LCD and buffer at 5V.

 

Last edited: Jun 6, 2008

Hero999

Banned

• Jun 6, 2008

• #3

Simple, use a low dropout regulator to get 3V3 and a level shifter IC to convert the 5V logic to 3V3.

 

Boncuk

New Member

• Jun 6, 2008

• #4

If you can get in India I suggest to use a stepup booster LT1615. It's maximum output current is about 350mA, more than you require for the LC-display.

LC-displays are normally 3.3V tolerant concerning data lines. They just won't get enough contrast with a supply voltage of 3.3V.

The LT1615 is easy to handle and comes in a SOT-23/5 package.

Boncuk

 

lord loh.

Member

• Jun 6, 2008

• #5

I was considering using a seperate power supply... That appears the simplest with minimum number of extra components.

 

Hero999

Banned

• Jun 6, 2008

• #6

Oh sorry, I got that backwards, you need to power a 5V LCD from 3V3.
What generates your 3.3V supply?

Is it generated from a higher voltage?

If so you might be able to skip the boost converter.

 

gramo

New Member

• Jun 6, 2008

• #7

This thread seems familiar

You would need to check the datasheet, eg this one specifies that the Logic Voltage must be 4.5-5.5V and the supply voltage to be 4-5V

In that case, running it purely from 3.3V would not be suffice, neither would interfacing it directly with a 3.3V device for logic communication

I am taking a guess to say that your supply voltage before the 3.3V regulator is over 6.5V, and setting up a second supply only takes 3 components;

**broken link removed**

 

Mikebits

Well-Known Member

• Jun 6, 2008

• #8

What about one of those LVC devices 3.3v to 5v and back level shifter ic's to transfer the logic signals?
One example:
**broken link removed**

Not saying this is the ideal part for your app, rather just to give an idea the level translators exist.

 

Last edited: Jun 6, 2008

blueroomelectronics

Well-Known Member

• Jun 6, 2008

• #9

lord loh. said:

Please don't ask me purchase a 3.3v module I cant find one in the local store and shall not be allowed to order one from Digikey or some such online store

Click to expand...

Building anything sans parts is always a bit of a challenge.

 

lord loh.

Member

• Jun 10, 2008

• #10

I used an additional L7805

I used an additional L7805 to power the LCD at Vcc and for the back light. The input levels from the microcontroller is 3.3v. It works okay.

Thanks a lot for the help.

 

S

SYE

Member

• Jun 10, 2008

• #11

Do your LCD routines use simple delays or do you check the busy flag ?
If you are checking the busy flag your LCD will output 5V, this could damage your 3.3V system. The safest way is to use delays.