Hnegi3's PIC-Powered Frequency Counter Displays Waveform

Hnegi3 has demonstrated a frequency counter that can even display the waveform, giving a user the option to specify which part of the input waveform to count. The design is based on Microchip's PIC24FJ64GC006IC MCU (with a built-in high-speed ADC) along with a character LCD to show frequency and a graphic LCD to display waveform.

"By applying an arbitrary bias voltage to the waveform, you can arbitrarily set the threshold value you want to count," Hnegi3 explains. "It is possible to measure by aiming at the fundamental wave part of the waveform with complicated frequency components or the ringing part of waveform including ringing such as overshoot and undershoot."

There are several pre-amplifiers on the input side of the circuit that amplify the input signal. This amplification factor is selected by the MUX (multiplexer). "By applying an arbitrary bias voltage to this signal with a DAC, the frequency can be counted at any part of the waveform," Hnegi3 adds. As shown in the block diagram, the frequency counter consists 16-bit software and 16-bit hardware. The character LCD is connected via I2C, while the waveform viewer through the SPI communication protocol.

This 18650 li-ion battery-powered device is capable of measuring DC frequency up to 48MHz. It has a maximum waveform observable sampling rate of 250ns per sample with frequencies above 2MHz are observed as beat components. The 99mm x 80mm measuring board can also be powered using a Li-ion battery charging board (if installed) via USB Micro B.

More details on the assembly of the PCB and instructions are available in Hnegi3's Instructable post.