Most simple frequency counter designs are based on the 74C926 integrated counter chip. Unfortunately, this device is now quite expensive and can only handle four digits which means the resolution isn’t all that great. By contrast, this alternative design is much lower in cost and has six digits for improved display resolution.

As presented, the circuit features two signal inputs. The first of these is fed directly to the main counter circuit and this gives a direct readout in Hertz (Hz) up to a maximum of 999999Hz (ie, just under 1MHz).

The second input is fed to the counter circuit via an onboard divider circuit or prescaler. This prescaler divides the input frequency by 1000, which means that the display now shows the measured frequency in kHz. As a result, the circuit can now measure frequencies up to about 40MHz.

Because the display reads directly in Hz or kHz, there is no need for decimal point switching and the associated complexity that this involves. There are no switches or controls – you simply feed the signal into the appropriate input for a direct readout in Hz or kHz.

Specifications Frequency Readout: 6-digit 7-segment LED display. Frequency Range: 1Hz-1MHz (1Hz resolution); 1kHz-40MHz (1kHz resolution). Can be easily modified for other ranges and resolutions. Input Signal Level: 5V TTL/CMOS compatible. Decimal Point Switching: Optional. Size: 116mm x 35mm x 25mm x 30mm. Supply Requirements: 5V DC @ 90mA.