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Topic: LCD I2C - Can't see - No PWM available (Read 406 times) previous topic - next topic

aiannar974

Hello - I am using a 16x2 lcd screen with a pro mini running 3.3v.  I am using every pin except the A6.  All are digital reads except A7, A4, A5.  A7 has a pot hooked to it and the A4, A5 have the lcd connected to them.  At first I thought the screen or my hookups were not working because I could not see anything, closer observation barely showed letters on the screen when the pot was set to full.  I thought I would hook the lcd up to a pwm pin to control the backlighting (I think the backlighting it too strong) but I do not have one available.  On the pro mini, the A6 and A7 pins cannot be used as digital pins so I cannot more a pin to them to free up a pwm pin.  I also tried the display with no backlighting and that was worse. 

What might my options be to solve this?  Should I switch to an OLED screen? 

Anthony

pert

Do you need to be able to control the backlight using your Arduino, or do you just need to set it to the desired brightness once and leave it there forever?

aiannar974

just need to set it once.  needs to be able to be read from 2 or 3 feet away

anthony

groundFungus

Is the LCD specified to run on 3.3V? 

aiannar974

I went back and looked at the specs.  It does say 5v.  I do have 5v that is being supplied to the pro mini.  Can I power the screen with the 5v and then use the sda and scl to communicate to the screen?

groundFungus

I use 5V I2C LCDs with 3.3V ESP8266.  I use bi-directional level shifters made with MOSFETS on SDA and SCL. 

Paul__B

If you are powering the LCD from 3.3 V, it is quite remarkable that you would see any text at all (unless it is a 3.3 V LCD which has a charge pump added to the PCB.  :smiley-lol:

You need to power the LCD module from 5 V and remove the two pull-ups on SDA and SCL on the backpack, providing your own 4k7 pull-ups to 3.3 V, not 5 V.

pert

The common PCF8574 I2C driver modules for LCDs have a jumper marked "LED". You can replace the jumper with a resistor to adjust the brightness of the backlight.

Paul__B

The common PCF8574 I2C driver modules for LCDs have a jumper marked "LED". You can replace the jumper with a resistor to adjust the brightness of the backlight.
Yes, I meant to mention that.  :smiley-lol:

bperrybap

#9
Jun 25, 2019, 11:02 pm Last Edit: Jun 25, 2019, 11:03 pm by bperrybap
The common PCF8574 I2C driver modules for LCDs have a jumper marked "LED". You can replace the jumper with a resistor to adjust the brightness of the backlight.
I've seen more than one design for the jumper.
I've seen these design variations:

-  jumper connects between power/ground and the LCD anode/cathode
(Removing jumper forces backlight off - this is the most common design - A resistor instead of the jumper lowers brightness when backlight is turned on by PCF8574 backlight pin

- jumper shorts PCF8574 backlight pin to ground or power
(jumper installed can either force backlight on or off depending on design - cannot use resistor instead of jumper for dimming)

- jumper is between PCF8574 backlight pin and transistor base
(jumper removed disables backlight control from PCF8574 backlight pin - jumper removed can either force backlight on or off depending on design - might be able use resistor instead of jumper for dimming)

--- bill


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