LCD Contrast Voltage on 16x2 LCD

[Joe.G]

Hi All,

Product - 20x4 Standard LCD using a similar HD44780 controller. The LCD is
standard and not extended tempreature. and Vlcd is near typically 0v.
(Vlcd is the contrast voltage pin)

1. I am interested in the methods used to set Vlcd (the contrast voltage).
Please comment .

2. Does the Voltage acrross the LCD planes (commons) very in production?

3. Can I use a single resistor to ground to adjust the Vlcd over the
operating tempreature range to set the contrast.

4. What other factors should I consider.


What are your thought on these questions?

Regards
Joe

 

[John Fields]

On Wed, 23 Mar 2005 00:26:43 +1100, "Joe.G" <joe.g@optusnet.com.au>
wrote:

Hi All,

Product - 20x4 Standard LCD using a similar HD44780 controller. The LCD is
standard and not extended tempreature. and Vlcd is near typically 0v.
(Vlcd is the contrast voltage pin)

1. I am interested in the methods used to set Vlcd (the contrast voltage).
Please comment .

---
Connect the ends of a pot from Vcc to ground and connect the wiper to
Vlcd.
---

2. Does the Voltage acrross the LCD planes (commons) very in production?

---
Who cares?
---

3. Can I use a single resistor to ground to adjust the Vlcd over the
operating tempreature range to set the contrast.

---
See 1., above.
---

4. What other factors should I consider.

---
Go to the LCD manufacturer's website for authoritative data.

--
John Fields

 

[Tim Mitchell]

In article <42401cdb$0$5599$afc38c87@news.optusnet.com.au>, Joe.G
<joe.g@optusnet.com.au> writes

Hi All,

Product - 20x4 Standard LCD using a similar HD44780 controller. The LCD is
standard and not extended tempreature. and Vlcd is near typically 0v.
(Vlcd is the contrast voltage pin)

1. I am interested in the methods used to set Vlcd (the contrast voltage).
Please comment .

2. Does the Voltage acrross the LCD planes (commons) very in production?

3. Can I use a single resistor to ground to adjust the Vlcd over the
operating tempreature range to set the contrast.

4. What other factors should I consider.

I always do it with a 10K preset from +5V to GND, wiper to Vlcd. Preset

is set on manufacture, works fine.

If the equipment will be subject to extremes of temperature you will
need to do some temperature compensation or the display will disappear
in the cold and go black in the heat.
--
Tim Mitchell