# I need to connect a lcd to an arduino without potentiometer.

I don't have a potentiometer at the moment, I have a few 1k resistors and a few 470 ohm resistors and I need to wire a lcd to arduino, I am a beginner - can anyone help me with proper circuit diagram, I tried the arduino lcd tutorial, nothing happened to the lcd.

The potentiometer is usually just for contrast control. Wire two of your 1K resistors end-to-end and put them in place of the contrast pot (the middle connection is the ‘wiper’). That should get you close enough to display stuff on the LCD. To 'fine tune" you can add a 1K or 470 resistor in parallel with one of the two sides of your ‘contrast pot’ to turn the contrast up or down. One of the five combinations of resistors should get you fairly good contrast:

±–1K—±–1K/470—+
±–1K—±–1K/1K—+
±–1K—±–1K—+
±–1K/1K—±–1K—+
±–1K/470—±–1K—+

The fixed values that work for me are a 4K7 resistor Vcc--> contrast pin (3) and a 330R resistor contrast pin (3) --> Gnd. (from an LCD display kit sold by PH Anderson)
The contrast pin wants to be at +.5 to +1V for "normal' LCD's and a small negative voltage for the "Extended Temp Range" LCD's.. 99% of all lcd's are of t'he common' type. HTH..

Bob

That should get you close enough to display stuff on the LCD.

I think that most LCDs will be blank with 2.5 v on pin 3.

I would start out by just connecting pin 3 to GND and see if the resulting display is adequate. It works quite well for my ancient Optrex displays.

In most cases you will need around 0.5 V or less on pin 3. This means that you need less than 1/10 of the 5 Volt supply that is usually used to drive the LCD controller and therefore your voltage divider resistance ratio should also be less than 1:10 with the lower resistance side between pin 3 and GND.

Since you don't have the resistors that Bob uses this puts John's first or last suggestion (depending on which end is GND) as the closest viable solutions with your available components, but it doesn't get you too close. Also, the total resistance is relatively low so you would be drawing more current from your power supply than is really necessary.

You would probably want several 470s in parallel on the low side and several 1Ks in series on the high side. Do the math!

Don

If you have 100uF capasitor, you can try this hack from hobbytronics. You will lose one digital port, but get possibility to change lcd contrast by arduino.

-Jafarin

Jafarin:
If you have 100uF capasitor, you can try this hack from hobbytronics. You will lose one digital port, but get possibility to change LCD contrast by Arduino.

As so often happens, there are just so many things wrong with that suggestion, such as grossly overloading Arduino pins to start with.

The notion that it is necessary to “adjust” the contrast is just one other, to say nothing of the awful diagram.

In any case, a common misunderstanding is that there is some need to use a potentiometer to set the voltage on Vo. This is in fact completely spurious. It happens that a 10k potentiometer was cited - clearly as a matter of convenience - in the original HD44780 datasheets and this has been mindlessly imitated by various users since. The fact that it is a 10k potentiometer (being perhaps the most commonly available value) and that only one tenth of its range at most is usable should strongly hint that the adjustment is anything but critical and is in fact “set and forget” (particularly with the inaccessible design of some of the I2C “backpacks”).

The point is that internally there is a resistor chain (R1 to R5, possibly R7) totalling 11k, connected back to Vcc. There is absolutely no need to parallel this with another resistor, that is, to connect any external resistor between Vo and Vcc . This does mean however that the value of a resistor you place between Vo and ground can be between zero and 1k - the latter to set Vo to about 0.45V.

So to start with, just try connecting Vo to ground. If that looks wrong, try a 470 ohm resistor to ground and depending on whether that gives the opposite effect, you can try other values. One resistor only required!

440 ohm between GND and Vo wil do the trick just fine