I have bunch of 16x2 LCD's from different manufacturers and I have bunch of mcu's that talk <3V3 only. I only tried to make them talk once and it didn't work the way I hoped (I attached the pull up's to 5V and connected everything to LCD) so I ended up adding 6 transistors to do a level shifting from 3V to 5V.
What are your experiences with driving 5V character lcd's with 3V logic?
I've used the 3.3V microcontrollers connected directly (except the R/W pin) with 5V LCDs without any troubles. I don't know if that's a good practice, but worked for me.
Good luck!
I have had it work and not work directly at 3.3volts. I have also used open drain pin types and pull-up, but could never get a max refresh rate high enough to make scrolling look smooth.
That's exactly what I'm worried about :( ... I have one 5V lcd that came with some coolrunner2 cpld dev board from digilent and it works perfectly with 3v, but attaching a "same looking, different brand" lcd instead mostly don't work .. sometimes the same lcd work for few days then stop working for few hours, then works again .. too bad .. and then ppl ask me why I love those small nokia 3310 spi lcd's :D
I've had major issues with this, even LCD's that were supposed to be run from 3V were a lot of trouble. Did manage to get them working in the end, with a 4.somethingV for the contrast pin. I really have a love/hate relationship with those LCD's, there's always something wrong with them...
Hey,
no its possible to run it at 3.3V logic.I had gone thru the schematics I found someplace online(cant locate em now) and ended deciding to short 'R7' (yes,usually all have the same R7,tried this hack with a few different LCDs) and you can have it going at 3.3V
heres a post from my blog on that : http://http://kmmankad.blogspot.com/2011/04/quick-lcd-hack.html
interesting, will try
Just looked at your blog and none of my lcd's here has anything similar to the resistor array you have on your picture :(
wrt contrast, make a negative voltage and bring it to the contrast pin, -2 or -3V should give you great contrast
[quote author="kmmankad"]Hey,
no its possible to run it at 3.3V logic.I had gone thru the schematics I found someplace online(cant locate em now) and ended deciding to short 'R7' (yes,usually all have the same R7,tried this hack with a few different LCDs) and you can have it going at 3.3V
heres a post from my blog on that : http://http://kmmankad.blogspot.com/2011/04/quick-lcd-hack.html[/quote]
I find that your method is very subjective to part manufacturing and performance of the components on an LCD module particularly the screen itself. 3.3V logic is possible for most LCDs but not for the power supply.
After analyzing your picture and the datasheet for HD44870 (http://http://www.adafruit.com/datasheets/HD44780.pdf), the resistor from the array are actually to divide the voltage supply to pins V1-V5 for proper drive waveform. In the datasheet, there are 2 types of bias which are 1/4 and 1/5 by which the former has V2 and V3 shorted while the later has them separated by another resistor. Each of them has a pot after the series of resistors which is the trimmer that we usually used for contrast adjustment. Also notice that later in the datasheet there is also requirement of more than 1.5V from VCC to V5, which means possible for 3.3V operation.
But one thing to note is that, although your LCD has 5 resistors in the array, that does not mean your LCD is made to the 1/5 bias configuration. I have a "relic" 40x2 LCD here using the original FP-80B package with 1/4 bias configuration and it has 5 resistors in the array. The first 4 resistors are wired for the 1/4 bias configuration from V1 to V5 while the last resistor is of 0 ohm and connect from V5 to contrast pin. That means if the contrast pin were to directly connected to ground, this last resistor in the series could be used for fixed contrast by applying the correct fixed value.
Here's my thought. You could be the lucky one to have LCD modules that has screens that could work at lower voltage. But the LCD modules has to be compliant with the standard LCDs out there. With 1/4 bias configuration the 5th resistor could be used to compensate for the lower voltage acceptance. From the picture of your LCD, it is obvious that there is a jumper pad for shorting contrast to the ground and from there, links to R7. I couldn't find any trace after R7 that connects into the chip under the plastic blob. So I really think that your LCD has 1/4 bias configuration with low voltage screen.