1602 LCD Internal contrast and brightness control J1 J2 J3 R1-R9 16x2

I notice there are some marked labels on my 16x2 LCD: J1 J2 J3 R1-R9 . Are there any expert who can tell me how these connections work? It seems to me that these resistors and jumpers can be connected in a way that they can be use to control brightness and contrast of the LCD. what I really want is that I don’t want to have that external to control the contrast, and don’t want to supply power through pin 16, 15 (A, K) to save some space for my project. I have read many of the datasheet. They don’t really make any sense to me, so of them even have J4, J5, which I can’t find on my board.

There are hundreds (probably thousands) of different LCD display modules out there that use the HD44780U compatible controller. They do not however all use the same circuitry on their pc boards.

I don't think the brightness of the LCD is adjustable and the contrast of the LCD is almost universally controlled by an external potentiometer.

Pins 15 and 16 have nothing to do with the LCD, they typically provide power to the backlight. Those resistors may be current limiting resistors for the backlight so you may be able to vary its brightness via the jumpers, but not the brightness of the display itself.

You may be able to power the backlight via connections near one end of the display but you will then need to provide external current limiting resistors.

We will be better able to determine what those resistors do if you provide good photographs of both sides of your module along with a link to it's datasheet.

Don

J1 to J3 are the jumpers that are used to configure the 3.3V version of the module when the adjacent U3 “charge pump” IC together with C1 and C2 are fitted to generate 6V from the 3.3V supply.

R1 to R5 (2k2 or “222”) are the resistors which provide from the contrast voltage, the six multiplexing voltages used to drive the display. R7 is an additional jumper (“000”) related to these contrast voltages. Nothing to fiddle with here.

R8 and R9 (when present) are the current limiting resistors for the illuminating LED. One is usually zero, the other 100 ohms (“101”) meaning you need no other limiting resistor to operate from 5V. If you don’t power the LED (pins 16 and 16) you will have great difficulty reading the display.

If you don’t want to use a potentiometer (or just a 470 ohm resistor between Vo and ground) to set the contrast, just connect Vo to ground. It will usually work acceptably, especially if the supply voltage drops a few hundred millivolts. :smiley:

Paul__B:
J1 to J3 are the jumpers that are used to configure the 3.3V version of the module when the adjacent U3 "charge pump" IC together with C1 and C2 are fitted to generate 6V from the 3.3V supply.

R1 to R5 (2k2 or "222") are the resistors which provide from the contrast voltage, the six multiplexing voltages used to drive the display. R7 is an additional jumper ("000") related to these contrast voltages. Nothing to fiddle with here.

R8 and R9 (when present) are the current limiting resistors for the illuminating LED. One is usually zero, the other 100 ohms ("101") meaning you need no other limiting resistor to operate from 5V. If you don't power the LED (pins 16 and 16) you will have great difficulty reading the display.

Thanks for the info. I understand R8 and R9, but the rest is not very clear to me, so how can I control the contrast of the LCD using R1-R7? Maybe I can't? I am pretty good at SMT soldering, and I have a stock of SMT resistors, so I really want to save external component for a cleaner project by doing onboard contract control.

floresta:
There are hundreds (probably thousands) of different LCD display modules out there that use the HD44780U compatible controller. They do not however all use the same circuitry on their pc boards.

I don’t think the brightness of the LCD is adjustable and the contrast of the LCD is almost universally controlled by an external potentiometer.

Pins 15 and 16 have nothing to do with the LCD, they typically provide power to the backlight. Those resistors may be current limiting resistors for the backlight so you may be able to vary its brightness via the jumpers, but not the brightness of the display itself.

You may be able to power the backlight via connections near one end of the display but you will then need to provide external current limiting resistors.

We will be better able to determine what those resistors do if you provide good photographs of both sides of your module along with a link to it’s datasheet.

Don

thank you. I understand about pin 15, 16 are just a connector to the LED backlight through R8, R9. One of them is 0 ohm, and one is 220 ohm. The thing I don’t understand is what those 3 jumpers do, and how to use R7 (0 ohm as well) to control the contrast of the LCD. My LCDs model is 1602A; I bought few of these from different sellers, and they are all the same pretty much. so I think there is a standard for these LCD modules.

... My LCDs model is 1602A; I bought few of these from different sellers, and they are all the same pretty much. so I think there is a standard for these LCD modules.

This is the first time that you have specified which module you are talking about. The ones you are familiar with are likely all the same because they are all copies of one specific original design.

The modules available in the decades before the introduction of cheap (and inexpensive) Chinese copies on eBay are likely to be different.

Don

arduinomagbit:
I bought few of these from different sellers, and they are all the same pretty much. so I think there is a standard for these LCD modules.

Indeed they are, apart from a few “outliers”.

As I explained before, the 3V version of the module (which is available, though I do not have one) is fitted with U3 as a “charge pump” IC. J1 to J3 either connect or bypass this voltage converter according to whether it is fitted or not.

R7 is in series with Vo. If you want not to have an external resistor setting the contrast, you need to connect a potentiometer - about 1k - between Vo and ground - note, as a variable resistor with the wiper connected to one end, two terminals only. Use this to determine the appropriate value and then measure it and solder a corresponding fixed resistor between Vo and ground. Now I am not sufficiently aware of the purpose of R7, but it may be appropriate to solder your resistor in place of R7 and just connect Vo directly to ground. It may in fact be sufficient simply to connect Vo directly to ground and be using a zero value of resistor; you can assess this for yourself with the potentiometer.