Circuit diagram
This project describes how to make a digital voltmeter with a PIC microcontroller. A character based on HD44780 LCD display is used to measure voltage. The PIC microcontroller used in this project is PIC16F688, which has 12 I / O pins of which 8 can be used as analog input channels to the built-in 10-bit ADC. The measured voltage is fed to one of eight analog channels.
The reference voltage for the AD conversion is chosen to be the supply voltage Vdd (+5 V). A resistor divider network is used to end the inning with a map of the range of input voltage range of ADC input voltage (0-5 V). The technique can show that the input voltage from 0 to 20 V, but can be expanded with an appropriate choice of resistance and make the calculation described below.
Since the PIC port can not be directly 20V input, the input voltage is reduced by using a resistor divider network simple. The resistors R1 and input voltage range R2-range of 0-20V to 0-5V, before being implemented in PIC16F688 channel analog input AN2. 5.1V zener diode connected in parallel between the port pin AN2 and earth provides protection to the PIC pin input voltage is accidentally beyond 20V. The LCD screen is connected to the 4-bit mode, and the head of CPSI makes firmware development easier than you can reprogram and test the PIC while it is on. When you’re happy and you want to transfer the circuit of the test card to a PCB or prototyping board for general purposes, it is not necessary ICSP header.S:
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