This frequency counter is practically classic example of MCU based device. It captures frequency pulses directly to MCY pin without any special prescalling circuitry or even protection. So it is capable to accept 3.3V CMOS level signals. But it is designed as module which can be integrated in to end device if needed. The counting workload is done by MSP430G2202 microcontroller which is capable to count up to 10MHz signals.
The display is connected to microcontroller using transistor based column selector decoded by 74HC238 and rows driven by MCU pins. One interesting feature included in this project is that counter can be calibrated to achieve +-10Hz error at 10MHz.