Using LEDs, LCDs and GLCDs in Microcontroller Projects

11.6 PROJECT 11.6 – Digital Voltmeter

This project is about the design of a digital voltmeter device with LCD output. The device can be used to measure voltages from 0 V to +5000 mV.

The voltage is measured and displayed every second. The measured voltage will be displayed in millivolts and in floating point format as follows:

11.6.1 Block Diagram

The block diagram of the project is shown in Figure 11.21.

Figure 11.21 Block diagram of the project

11.6.2 Circuit Diagram

The circuit diagram of the project is shown in Figure 11.22. The LCD is connected to PORT B as before. The analogue voltage to be measured is applied to port pin RA0 of the microcontroller, and this pin is configured as an analogue input pin. The project is based on a PIC18F45K22 type microcontroller with an 8 MHz crystal clock, although most other PIC microcontrollers supporting A/D converters can also be used.

Figure 11.22 Circuit diagram of the project

The connections between the microcontroller and the LCD are as follows:

LCD Pin	Microcontroller Pin
D4	RB0
D5	RB1
D6	RB2
D7	RB3
R/S	RB4
E	RB5

The contrast of the LCD is controlled by connecting a 10 KB potentiometer to pin 3 of the LCD. The microcontroller ...