QC1602A (v2.0) Contrast not working?

Hi,

i just started playing around with components.
Im following this guide to use my LCD with an Arduino UNO: http://www.dreamdealer.nl/tutorials/connecting_a_1602a_lcd_display_and_a_light_sensor_to_arduino_uno.html

To the point where i wired the LCD and got the backlight on everything seems ok.

After i wired the potentiometer as shown(mine is 50K), trying to operate it doesn’t result in any change on the screen, i dont see any of those black square.

I did search in google without luck- I tried through code to change the contrast with analogWrite as shown here: http://engineeringlearning.blogspot.fi/2013/10/interfacing-lcd-without-potentiometer.html but no change.

Can it be that something is wrong with the LCD?

Any suggestion is appreciaated. :blush:

Thanks

Some breadboards have a break at the center of the horizontal bus bars that you are using for +5V and GND. Typically those breadboards also have a break in the blue and red lines painted next to those buses but you never can tell.

If you don't have a voltmeter to check things out then just connect the potentiometer feeds left of the center of those buses and see what happens.

Don

It is difficult to make out but I cannot see solder on the connections of the LCD.

Apparently you are using pin headers to connect the LCD into the breadboard. Surely you are not just resting the LCD module on the pin headers and expecting them to contact? And are they actually firmly located in the breadboard?

A 50k potentiometer is a somewhat high value but should provide contrast turned to the ground end. In fact, you should get contrast with pin 3 connected straight to ground - pin 1 - when using a 5V supply.

Clorofilla: I tried through code to change the contrast with analogWrite as shown here: http://engineeringlearning.blogspot.fi/2013/10/interfacing-lcd-without-potentiometer.html but no change.

Somehow I suspect that article is total garbage! PWM is inappropriate for this purpose (and certainly without a low-pass filter)

Clorofilla: Can it be that something is wrong with the LCD?

Some LCDs do require different voltages. We might have no idea as you have not cited a link to the one you are using, however the somewhat garbled and unhelpful datasheet for the QC1602A implies that it should work just fine at 5V.

Thanks for the answers.

That is the correct datasheet for the LCD.

I now realize as Paul pointed out, the pin headers being not soldered to the LCD may cause the problem (in the example i was following i just noticed they were soldered indeed :blush:).

Is there anything i can do to make a stable connection to the LCD's pins while i wait for the soldering equipment?

There is no way to do that. You might think you'd be able to press the LCD board to the header pins, but that would in no way be stable. Bending the header pins might also seem to be a good idea, but these pins typically don't bend that well, and you'd have to have some header with pins that are longer than standard.

Soldering is the way to go. And practice a bit before you do the soldering to you LCD board. There have been some pictures on this board, showing really horrible soldering jobs, asking what might be wrong with that setup.

alright, thanks for the info, i will then solder it