PIC16F1827 counter uses Real Time Clock 2 PPM crystal oscillator. The PIC sets the DS3231 module to output accurate 1 Hz which is used to gate the input frequency, I use this module because it is cheaper than other 2 PPM crystal oscillators. The 3V battery isn't needed. Measuring the 32768 Hz output of the module gives exact readings.
The frequency is displayed on line 1 by 8 digits with leading zeros removed down to 3 digits. Signal input is a TTL type.
Period is displayed on line 2. The period is calculated. For frequencies greater than 1000Hz the display is ns and for less than 1000Hz the display is in us (micro sec).
Contrast trimmer can set contrast from zero to max, set the trimmer to about middle to start with. Included C code and circuit diagram. The LCD and driver module is a 2 lines 16 characters. The LCD is driven by 4 bits data bus.

Counter uses PIC16F1827 . The frequency range is 0.25Hz to 10KHz displayed in millihertz. Included C code and circuit diagram. The LCD and driver module is a 2 lines 16 characters. The LCD is driven by 4 bits data bus. The frequency is displayed on line 1 by 8 digits with leading zeros removed down to 4 digits.
The software counts the number of pulses of 1MHz oscillator during 1 cycle of the input and then calculates 1 billion divided by counts and the result is in milliHz.
The input is connected to the inverting input of the comparator and the non inverting input is connected internaly to 2.5V. The input signal can be down to 0.1VAC and 2.5VDC.
Contrast trimmer can set contrast from zero to max, set the trimmer to about middle to start with.

Counter uses PIC16F1827 . Included C code and circuit diagram. The LCD and driver module is a 2 lines 16 characters. The LCD is driven by 4 bits data bus.
The frequency is displayed on line 1 by 8 digits with leading zeros removed down to 3 digits. Signal input is a TTL type. The time base is generated by the 8MHz crystal oscillator using timer1 and CCP1.
The counter measure the frequency for 0.1sec first, if the frequency is greater than 2MHz TMR0 prescaler divides by 2 to increase the input frequency range to 16MHz with resolution of 2Hz, if the frequency below 2MHz TMR0 is set for no prescaling and the measurment is with resolution of 1Hz.
Period is displayed on line 2. The period is calculated. For frequencies greater than 1000Hz the display is ns and for less than 1000Hz the display is in us (micro sec).
Contrast trimmer can set contrast from zero to max, set the trimmer to about middle to start with.

Counter uses PIC16F628A . Included C code and circuit diagram. The LCD and driver module is a 2 lines 16 characters. The LCD is driven by 4 bits data bus.
The frequency is displayed on line 1 by 7 digits with leading zeros removed down to 3 digits. Signal input is a TTL type. The time base is generated by the 20MHz crystal oscillator using timer1 and the CCP.
Timer0 is used to count the input frequency up to 5MHz with resolution of 1Hz
Period is displayed on line 2. The period is calculated. For frequencies greater than 1000Hz the display is ns and for less than 1000Hz the display is in us (micro sec).
Contrast trimmer can set contrast from zero to max, set the trimmer to about middle to start with.

Counter uses PIC16F628A . Included C code and circuit diagram. The LCD and driver module is a 2 lines 16 characters, it has 14 way connector. The LCD is driven by 4 bits data bus.
The frequency is displayed on line 1 by 7 digits with leading zeros removed down to 3 digits. Signal input is a TTL type. The time base is generated by the 32768Hz crystal oscillator. The CPU frequency is 4MHz from the internal oscillator.
The lcd_counter2MHz firmware is the older version it counts up to 2MHz only.
The lcd16mhz firmware resolution is 1 Hz for frequencies up to 1 MHz and 8 Hz for frequencies over 1 MHz.
The counting is first for a period of 1 second with resolution of 8 Hz and if the frequency is over 1 MHz it is displayed. If the frequency is less than 1MHz the counting is repeated for a period of 2 seconds with resolution of 1 Hz and then displayed.
I tested the counter at up to 2MHz, I don't have the means to test higher frequencies.
Period is displayed on line 2. The period is calculated. For frequencies greater than 1000Hz the display is ns and for less than 1000Hz the display is in us (micro sec).
Contrast trimmer can set contrast from zero to max, set the trimmer to about middle to start with.

Counter uses ATtiny85/45, included .ino file and circuit diagram. OLED 0.96'' 128x64 or OLED 0.91'' 128x32 pixel driven by I2C interface and using SSD1306 driver IC. ATtiny drives the Oled using software I2C.
ATTINY is programmed using Arduino IDE and Arduino as ISP. Use these instructions https://gist.github.com/ij96/804e731bd31dbb95b2b043e93c79ceab with the difference of burning bootloader with setting "Clock Source 16MHz external", this makes the CPU work at the crystal frequency.
The frequency is displayed by 7 digits with leading zeros removed down to 3 digits. Signal input is a TTL type. The time base is generated by the 16MHz crystal oscillator.
The counting resolution is 1 Hz for frequencies up to 6 MHz.

Counter uses PIC12F629 . Included C code and circuit diagram. HEX file is included. OLED 0.96'' 128x64 or OLED 0.91'' 128x32 pixel driven by I2C interface and using SSD1306 driver IC. Pic drives the Oled using software I2C. For OLED 128x32 code line 11 has to be commented. HEX files for both size OLED are included.
The frequency is displayed by 7 digits with leading zeros removed down to 3 digits. Signal input is a TTL type. The time base is generated by the 32768Hz crystal oscillator. The CPU frequency is 4MHz from the internal oscillator.
The counting resolution is 2 Hz for frequencies up to 2 MHz.
OLED 128x64 from ebay: https://www.ebay.co.uk/itm/0-96

Counter uses PIC16F628A . Included C code and circuit diagram. Color Oled display 0.95", 96 x 64, SSD1331 driver. Pic drives the Oled using software SPI.
The frequency is displayed on line 1 by 7 digits with leading zeros removed down to 1 digits. Signal input is a TTL type. The time base is generated by the 32768Hz crystal oscillator. The CPU frequency is 4MHz from the internal oscillator.
The counting resolution is 1 Hz for frequencies up to 2 MHz.
Period is displayed on line 2. The period is calculated. For frequencies greater than 1000Hz the display is ns and for less than 1000Hz the display is in us (micro sec).
OLED module: https://www.ebay.co.uk

The project is for Arduino Uno or Nano. The Arduino generates an accurate 1 second time base for the counter by cascading timer0 and timer2. The link between digital inputs 3 and 4 connects the output of timer2, 250 Hz, to input of timer0. The software waits for the output of timer0 to go positive to start the count of frequency input to timer1. Timer1 is a 16 bits timer, it overflows at the count of 2 power of 16, that in turn advances over-flow register. At the end of the 1 second the 16 bit register is recorded. The Arduino then calculates the frequency and period and displays them on the LCD.
There is a big selection of LCD modules, and they are very similar in characteristics . The LCD module has to be HD44780 compatible.
The frequency input is TTL signal levels. The MCU spects recommend input up to 6 MHz, I tested it at 2 MHz.
Contrast trimmer can set contrast from zero to max, set the trimmer to about middle to start with.

You are free to use the circuit diagram and the software with no limitations.