User manual

a very low scatter of the electrical properties by now, the

technology used in the learning package can also be used with

a single fixed resistor. For this, we use a 2.2-kΩ-resistor that

is placed between the ground and the contrast connection Vee of

the LCD to firmly set the contrast.

When using a potentiometer without ballast, the adjustable range

that affects the contrast is very low, however. For a better

spread of the contrast range, it is recommended to Switch a

corresponding ballast between Vcc (+5 V) and one end of the

potentiometer.

The voltage at the pin Vee should be adjustable between 0 and

1.5 V. This circuit is suitable for an ambient temperature of

0 to 40 °C. If the adjustable range is not optimal, (some LCDs

deviate from this), we need to change the ballast. Practical

values are in the range from 10 to 22 kΩ.

If we use the display outside of the normal temperature range

(0 to 40 °C), it is recommended to perform the wiring as shown

in the circuit diagram above. This circuit adjusts the contrast

to the ambient conditions. The temperature will be measured with

a temperature sensor NTC (Negative Temperature Coefficient

Thermistor) that will shift the contrast voltage via the

PNP-transistor. The LCD-modules can no longer be read properly

at too-low temperatures below 0 °C. The contrast is tempera-

ture-dependent.

5.8 | The Character Set

The displays have a character set that is firmly integrated in

the display controller. By sequencing the upper and lower 4 bits,

the data byte for the corresponding ASCII-character will be

formed. Example of the ASCII-character A: 01000001

Let us do an experiment with the LCD-character set. The following

program code shows how you can write the characters from the

character table onto the display. Special characters like the

degree symbol or the Ohm symbol are not possible via a strong

output. Since this is the expanded character set of the LCD ,

we need to do so using the character table.

001 lcd.write(B11110100)

Here, we will write the binary value in the display controller

to output the Omega character. The B at the beginning of the