PIC16F870 Based LC Meter

The project illustrates a measuring tool based on PIC16F870 microcontroller that would calculate the inductance and capacitance.

The main components included with the PIC16F870 microcontroller are the oscillator LM311 and a standard 16 characters by 2 lines LCD display. A 4-wire mode is used to connect the display to the PIC. The PIC is being operated by a 4MHz crystal while the LC oscillator based around IC2 is the heart of the construction. The frequency comes out at Pin 7 and then enters the PIC at Pin 11.

To prevent stray inductance/capacitance and to ensure making the measurement more automatic, two relays have been added. The relays keep the stray inductance/capacitance down to a minimum level while improving the accuracy. This is why the relays are preferred over switches that get connected using long wires. They also keep the current consumption to a constant low level while the 4 transistors are used to control the two relays. The measurement will be affected if the current fluctuates and for this reason, a double-coil latch type relays were used.

The 4 wires from the transistors Q1-Q4 should be connected to the relays before soldering the LCD.

Rest of the project