Reciprocal frequency counter with Pi Pico. Using four of the internal pwm-counter for counting the input pulses and the reference clock alternately without gap.
Only a few components are required:
- Pi Pico
- 74AC02
- 74AC74
- 10MHz-XO
- LCD-Display with I2C-Bus
This reciprocal frequency counter has a resolution of 7 digits at one second gate time and 8 digits at 10s gate time. The time base error of the used TCXO (IQD CFPT-126) is smaller then the resolution so when tested with the 1pps-signal of a gps-receiver the error is ±1 count in the least significant digit.
With the "range"-switch, the gate time can be changed between 0.25s, 1s and 10s.
The calibration process is started by pressing the "cal" button until "Calibration" is shown on the display. A precise 1Hz signal is required at the input for calibration. After calibration, the correction values are stored on the flash memory.