[SOLVED] LCD PC1602-H contrast problem

[mariuszoll]

Hi,

I use on my project a LCD PC1602-H from PowerTip. I connected Vo to GND, but I can barely see what is displayed on the display. The software works well.
I read on forums that the LCD works well with Vo connected to -1.2V.
Could you help me please with some ideas of getting this negative voltage with only discrete components?

I'm looking forward to hearing from you.

Thank you in advance.

 

[amayilsamy]

Read this data sheet.

https://www.farnell.com/datasheets/50573.pdf

Page # 18. It have details about Contrast adjustment of LCD . Vo Schematic.



I hope Its helps you

 

[mariuszoll]

I tried to do it internal, by making a short on J2, and I played a little bit with the values of R7 from 0 to 4k7, but without positive results.

 

[amayilsamy]

Try this schematic .

.

Use single power source.

 

[mariuszoll]

I made the following test:
I supplied pin Vo through a 4k7 with negative voltage. I noticed that, starting with -1.3V the contrast improved and I can read what is displayed.
At -1.6V the characters can be read very well. I am thinking to a possible solution with diodes connected in series.

 

[bigdogguru]

The vast majority of HD44780 compatible displays in production today, do NOT require a negative voltage be applied to Vo.

Typically a 10kΩ pot used in the manner indicated by the schematics posted by amayilsamy should suffice.


BigDog

 

[mvs sarma]

Perhaps a combination of 8.2K and 1.5 or 1.8K would be cheaper solution.instead of diodes whose voltage drop changes with temperature.

 

[mariuszoll]

As far as I seen, LCDs that are used in a wide range of temperatures, like PC1602H use a negative voltage for the contrast. The necessary voltage I got it from the MAX232 charge pump(pin 6) with a voltage divider.

 

[bigdogguru]

As far as I seen, LCDs that are used in a wide range of temperatures, like PC1602H use a negative voltage for the contrast. The necessary voltage I got it from the MAX232 charge pump(pin 6) with a voltage divider.

Apparently you have not seen or bothered to review the Powertip PC1602-H Datasheet available from Farnell.

Reference: Powertip PC1602-H Datasheet, Section: 1. Adjusting the contrast of a character LCD module.

Which clearly recommends the use of a 10kΩ to 20kΩ between Vdd and Vss (GND) to bias the contrast (Vo) as previously suggested.


BigDog

 

[mariuszoll]

Hi,

Unfortunately, I tried with a 50K pot, because I didn't have such a pot provided by the datasheet. The result wasn't very good, the contrast was very poor. Then, I connected the Vo line through a 4k7 resistor to a power supply, and I applied a negative voltage to the pin, based on some comments from the forums.
Astonishing, the results started to reveal starting with a -1.3V, at -1.6V the contrast is very good, and the characters can be read without problems.

 

[mvs sarma]

Nice that you had overcome the issue.
in fact , had you tried my solution at post#7 you get same result. i even make it more simple like one single 1K or 1.2K resistor from pin3 to ground suffices. I generally use a single 1N4148 diode in that place with cathode to ground.