Frequency Counter 2Hz ... >60MHz Using The ATtiny424's "EVENT" System

* Sequence control via the ATtiny424's "EVENT" system and  RTC Interval Timer.
  This means, that timers TCB0 and TCB1 are configured in CAPTURE mode via PINA1
  as a 32-bit reference counter and TCA0, also via PINA1, as a 16-bit measurement counter.

* Reference clock via the inexpensive TCXO TG2520SMN 20MHz, temperature coefficient < 5*10^-7,
  frequency deviation can be adjusted in the software (F_CPU in 'lcd_drv.h'). The TCXOs I 
  owned, have a deviation of < 5*10^-8 (measured with a GPS-guided counter)!

* The firmware was created with Microchip Studio 7. The memory usage is approximately 80%.

* Reciprocal frequency measurement. Displaying 7/8 digits (f > 10Hz).

* Power supply 5V DC, preferably via USB. The "power bank keeping alive" can be switched off.
  Reverse polarity protection exists.

* The power voltage is displayed (resolution 5mV)
  Scaling can be adjusted in 'main.c' <#define U_K 32233UL>
 
* The potentiometer controls: Switching between frequency display and period display
                              Gate time: 1 to 9 s
                              Switching off the "power bank keeping alive"

* Sensitivity is <15mV RMS 5Hz to 10MHz, <50mV RMS <60MHz.

* PCB software: Target V33make.

* PCB was created using toner transfer, therefore only center holes are present.

* Mostly components of my stock were used, which can often be replaced with similar parts.