Frequency and LC Meters

Here we have put the diagrams of our devices for measuring frequency, inductance and capacitance.

Options

• Frequency meter v3.1 (2003 – 2007)
  • 1Hz – 1000MHz
• Frequency meter with functions v2.4 (2004 – 2005)
  • F1: 1Hz – 1000MHz
  • F2: 1Hz – 50MHz
  • F3: 1Hz – 50MHz
• Frequency and LC meter v1.2 (2005 – 2008)
  • 1Hz – 60MHz
  • 0.01pF – 150nF
  • 150nF – 1uF
  • 0.001uH – 100mH

If you have an interest in any of the measuring instruments, we can produce one for your own use. For a price quote and device manufacturing time information, please contact us: LZ2GL

Frequency Meter Gallery

L/C Meter Gallery

Other Meters Gallery

Description

We started making a frequency meter with PIC16F84A for the first time using schemes on the Internet in 2003. We also wrote the program using material from Microchip and other developments, which we found on the Net. The device was started in early 2003 and by the end of March the same year we launched the first version. It measured quite well, although there were some errors in the software.

In the next 2004 we came up with the idea to make the frequency meter more sophisticated, or strictly speaking to just make another device, which can be measure three frequencies simultaneously and to make arithmetical calculations between them. One such important calculation turned out to be F1 – (F2 + F3), where: F1 – is the frequency of the radio synthesizer, F2 – is the frequency of the first intermediate and F3 – is the frequency of the second intermediate. With this device you can measure exactly at what frequency can transmit an amateur radio transceiver with one or two conversions.

In 2005, after a short research, and with experience already gained around the new transceiver and its program, we improved the software of both types of frequency meters, as we improved the code and key reading and corrected a small error in main cycle of times. This error generated the following anomaly: at precision of 10Hz -> 10.000.01Hz the last character was fluctuating between 0 and 1. That is normal, but moving to a higher step 10KHz -> 10.02kHz here the last digit was fluctuation between 1-2 instead of 0 and 1. It turned out that we had not foreseen 1 instruction in the time cycle, and that was a combination of half an instruction for opening and half for closing the Freq Gate. The main cycle of time is developed by us with 4 levels of nesting. This yields a good combination of number of cycles and number of possibilities for selecting the times for the various factors that are put in front of the frequency meters, of 64 or 256. This allows the device to measure frequencies of 1000-1500MHz.

Then we decided to also make an LC meter, it turned out that we need a microcontroller to measure the frequency of an LC generator and a lot of calculations. Formulas and schemed of that generator can be found in many places on the Internet. A good place is L/C Meter IIB by Neil Heckt.

The program is developed by us, and we added the calculations needed for the frequency meter to it. It turned out that floating-point operations Microchip AN575 were required, therefore the code increased significantly reaching the 1Kb code page limit of PIC16F84. So we decided to use PIC16F88(PIC16F628/648), they are identical in terms of the placement of feet for core functions and memory is sufficient.

It is possible that the device can be made with PIC16F84, by removing the function of a frequency meter (to reduce the code) and leaving only the LC measurement, but I found out that the price of a common processor is much more expensive than the cost of new processors PIC16F88, simply because Microchip’s costs are less to produce based on newer technology, and due to the demand for the older model it has a greater price. Which is absurd and therefore it is better to use the new models that have a lot more features, memory, and as it turns out, greater sensitivity when measuring frequency.

After the release, the device was calibrated with standard inductance and capacitance from a laboratory in Veliko Tarnovo, after which the error of the device reached about 1% for the ranges 1pF-100nF and 1uHy-1mHy, and for other ranges the error was not measured, but is believed to be about 1-2%.

In 2007 we upgraded the frequency meter to version v3.1. We removed 74HC164 to save consumption, and we made a 4 bit interface for the LCD. We also changed the current divider, and we began to use PMB2313T for the high frequency input. This divider is in SMD format and has very good parameters in the range 50MHz – 1.1GHz. We also changed the design to PCB, to fit in a smaller box, and started using an SMD format for most of our components.

In 2008 we upgraded the LC meter to version v1.2. We changed the design to PCB of this device too, to fit in a smaller box, and started using an SMD format for most components. As additional option we tested 74AC132 and reached a very good maximum frequency of measurement, up to 60MHz without a high-frequency divider.

Datasheets

• PIC16F84A
• PIC16F88
• PIC16F628/648
• Microchip AN575
• PMB2313T

Schematics