Can someone kindly explain to me how I would construct positive voltage of 3.3v at one end of a 4k7 ohm trim-pot with -3.3v at the other end as I want the ability to change my voltage from 3.3v to -3.3v with a center tap. Please reference why I need this here: http://www.lcd-module.de/eng/pdf/doma/dips082e.pdf
On page two at the top right under the contrast setting it shows what I explained above but I need some help getting me there.
Thank you for your kind assistence.

P

 

The simplest way is to use an ICL7660 to generate the negative voltage.

 

If it is being used in a unit without a bipolar supply then put the pot between 5V and Ground instead - per the datasheet. If you have a bipolar supply then what's the problem?

 

If it is being used in a unit without a bipolar supply then put the pot between 5V and Ground instead - per the datasheet.

I believe that he is running the display at 3.3 volts, not 5 volts. The 3.3 volts requires a negative LCD bias to get full contrast adjustment range.

 

I believe that he is running the display at 3.3 volts, not 5 volts. The 3.3 volts requires a negative LCD bias to get full contrast adjustment range.

Yes I am trying to figure out whether or not I can just run it with the pot between 3.3v and ground or if I HAVE to use 3.3v/-3.3v. as I am getting nothing on my output now (3.3v and ground) and want to know if this is the reason why. This is my first attempt at using a LCD display.

Peaches

 

Yes I am trying to figure out whether or not I can just run it with the pot between 3.3v and ground or if I HAVE to use 3.3v/-3.3v. as I am getting nothing on my output now (3.3v and ground) and want to know if this is the reason why. This is my first attempt at using a LCD display.Peaches

I think so. A typical LCD needs about 5 volts of bias. That is why grounding the bias pin when powered from 5 volts works. To get the equivalent 5 volt of bias when running on 3.3 volts you need about about -1.7 volts of bias.

 

I think so. A typical LCD needs about 5 volts of bias. That is why grounding the bias pin when powered from 5 volts works. To get the equivalent 5 volt of bias when running on 3.3 volts you need about about -1.7 volts of bias.

Ok, I see. Could you explain to me the easiest way for me to do this? 3.3v, -3.3v as per the datasheet. (I have never done anything w/ neg voltage before and not sure how to do this). Thank you for your help.

Peaches

 

Ok, I see. Could you explain to me the easiest way for me to do this? 3.3v, -3.3v as per the datasheet. (I have never done anything w/ neg voltage before and not sure how to do this). Thank you for your help. Peaches

See posr #2.

 

I think so. A typical LCD needs about 5 volts of bias. That is why grounding the bias pin when powered from 5 volts works. To get the equivalent 5 volt of bias when running on 3.3 volts you need about about -1.7 volts of bias.

Ok, I see. Can you explain to me what would be the easiest way to create 3.3v and -3.3v as per the datasheet? (I have never done anything with negative voltage before and really need some guidance here). Thank you for your help.

Peaches

 

Is there any other way?

 

Is there any other way?

At least a million but few would be simpler.

 

If a micro is in use, a IO pin available and adding some code is possible, a negative voltage could be obtained from there.

 

Is there any other way?

For testing, a couple of 1.5 volt cells in series will do it.

 

One simple way is to forget about the -3.3 v and instead make both positive 5v and 3.3 volt power from your main supply.

Power the display with 5v and the micro and the rest off the 3.3 volt. Yes the display will work just fine with 3.3 volt signals on the data lines.

 

The simplest way would be to use a 3V coin cell. -3V should be plenty to get the correct contrast.

Connect the + terminal of the battery to ground and the - terminal will then be -3V.

Bob