Adjusting the contrast on an LCD screen depends on the type of display you are using. For consumer monitors, laptops, or televisions, this is typically done through on-screen menus. However, for certain LCD displays, often found in electronics projects (like character LCD modules), the contrast is adjusted differently using a physical control and a dedicated pin.
Adjusting Contrast on Specific LCD Types
For many small character and graphic LCD modules, such as those commonly used with microcontrollers, the contrast is controlled via a dedicated connection pin and a voltage input.
The Contrast Pin
These LCDs have a contrast pin, which is typically pin 3 on standard parallel interface displays. The contrast of the pixels is adjusted by a voltage into this pin.
Physical Adjustment on the Board
On the LCD module itself, there is usually a physical component designed to easily control this voltage. You can adjust the contrast by the area designed into the top right corner of the board. This area commonly contains a small potentiometer (a variable resistor) or a trimpot.
How Voltage Affects Contrast
The contrast level is directly tied to the voltage supplied to the contrast pin. According to how these types of displays function:
- Setting the contrast pin to a lower voltage makes the LCD contrast higher. This makes the lit pixels appear darker and stand out more against the background.
- Conversely, applying a higher voltage to the contrast pin will decrease the contrast, potentially making the pixels appear faint or invisible.
Adjusting the potentiometer on the board changes the voltage supplied to pin 3, allowing you to find the optimal contrast level for readability.
Practical Example: Using a Potentiometer
A common method to provide a variable voltage to the contrast pin (pin 3) is to use a 10k ohm potentiometer.
- Connect one outer leg of the potentiometer to the LCD's power supply (VCC, typically +5V).
- Connect the other outer leg of the potentiometer to ground (GND).
- Connect the center leg (wiper) of the potentiometer to the LCD's contrast pin (pin 3).
By turning the shaft of the potentiometer, you vary the voltage at the center leg, which in turn adjusts the contrast of the LCD pixels.
Summary: Adjusting Contrast on Character/Graphic LCDs
To adjust the contrast on LCDs featuring a contrast pin:
- Locate the contrast adjustment component, often found in the top right corner of the board (usually a potentiometer/trimpot).
- Turn the potentiometer/trimpot using a small screwdriver or knob.
- Monitor the display as you turn it to find the desired level of contrast.
- Remember that setting the contrast pin (pin 3) to a lower voltage results in higher contrast.
While standard consumer displays use menu-based adjustments, understanding the role of the contrast pin and voltage is key for working with many small electronic LCD modules.