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Very Accurate LC Meter based on PIC16F84A IC

Very Accurate LC Meter based on PIC16F84A IC

This is claimed as a very accurate and simplest LC inductance capacitance meter. It allows you to measure incredibly small inductances starting from 10nH to 1000nH, 1uH to 1000uH, 1mH to 100mH and capacitance from 0.1pF up to 300nF.
The circuit uses an auto ranging system so that way you do not need to spend time to select the ranges manually. Another neat function is the “Zero Out” momentary switch that will reset the initial inductance / capacitance, making sure that the final readings are as accurate as possible.

The LC Meter uses a popular LM311 IC that that functions as a frequency generator and this is exactly what we need. If we want to calculate the value of an unknown inductor we use a know Ccal 1000pF capacitor and the value of an unknown inductor. LM311 will generate a frequency that we can measure with a frequency meter. Once we have this information we can use the frequency formula to calculate the inductance.


The same thing can be done for calculating the value of a unknown capacitor. This time we don’t know the value a capacitor so instead we use the value of a known inductor to calculate the frequency. Once we have that information we apply the formula to determine the capacitance.

In the next step we use the frequency generated by LM311 IC and pass it on to PIC16F84A’s PIN 17. We designate this PIN as an input, as well as all other PINs that are directly connected to switches and jumpers. User can use these inputs to tell the microchip to execute specified set of instructions or perform calculations.

Once the microchip will calculate the unknown inductance or capacitance it will use PINs that are designated as outputs and pass the results on to the 16 character LCD display.

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