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Computer Controlled Frequency Counter

Computer Controlled Frequency Counter

This circuit is a stable frequency counter accurate to 5 significant digits. The range is 0 – 30MHz with an input sensitivity of greater then 100mV. The probe connects to the PC serial port.
So by using the crystal oscillator already present on your PC serial card and software calibration, the Probes’ external circuitry is kept to a minimum. Probe 9 can also be used as a logic probe/analyzer using included software .

Part Total Qty. Description Substitutions


R1,R2,R3,R4 4 100K 1/4W Resistor
R5 1 10M 1/4W Resistor
R6, R7 2 3.3K 1/4W Resistor
R8 1 390 Ohm 1/4W Resistor
R9 1 1M 1/4W Resistor
C1, C4 2 0.1uF Ceramic Disc Capacitor
C2, C3 2 100uF 16V Electrolytic Capacitor
D1 1 1N4148 Signal Diode Any 200mA silicon signal diode
D2, D3 2 3.3V Zener Diode
D4 1 6.2V Zener Diode
U1 1 74HC00 Quad Highspeed NAND Gate
U2, U3, U4 3 4021 8 Stage Shift Register
U5 1 74HC393 Dual Highspeed 4 Bit Counter
U6 1 4040 12 Stage Binary Counter
MISC 1 PC Board, Wire, Suitable Pro be, DB9/DB25 Connector

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