Electronic projects

Precision Frequency generator 1 to 999 Hz
Precision Metronome 1 to 999 beats per minute

Circuit diagram

Parts:
R1 1M 1/4W Resistor
R2 22K 1/4W Resistor
R3 6K8 1/4W Resistor
R4 4K7 1/4W Resistor
R5 47K 1/4W Resistor
R6 100K 1/4W Resistor
R7 39K 1/4W Resistor
R8 12K 1/4W Resistor
C1 47pF 63V Ceramic Capacitor
C2 2-22pF 63V Ceramic Trimmer
C3 470pF 63V Ceramic Capacitor
C4 10pF 63V Ceramic Capacitor
C5 100nF 63V Polyester Capacitor
C6 220nF 63V Polyester Capacitor
C7 22µF 25V Electrolytic Capacitor
D1-D15 1N4148 75V 150mA Diodes
IC1 4060 14 stage ripple counter and oscillator IC
IC2 4082 Dual 4 input AND gate IC
IC3 4520 Dual binary up-counter IC
IC4 4518 Dual BCD up-counter IC
IC5 4046 Micropower Phase-locked Loop IC
IC6 4040 12 stage ripple counter IC
Q1 BC337 45V 800mA NPN Transistor
XTAL 2.4576 MHz Miniature Quartz crystal
SW1 BCD Miniature Thumbswheel Switch (units)
SW2 BCD Miniature Thumbswheel Switch (tens)
SW3 BCD Miniature Thumbswheel Switch (hundreds)
SW4 SPST Slider Switch (On-off)
SW5 SPDT Slider Switch (Metronome-Pitch)
SPKR 8 Ohm, 50 mm. Loudspeaker
B1 9V PP3 Battery
Clip for 9V PP3 Battery

Circuit operation:
CMos IC1 and IC2B quad AND gate form a 2.4576 MHz crystal oscillator plus a 2400 times divider. IC3A provides further division by 16, obtaining a 64 Hz stable frequency square wave. This frequency is multiplied by operation of Phase Locked Loop IC5, double decade divider IC4 and IC3B 4 bit binary divider, by the number set by three miniature BCD thumbswheel switches SW1, SW2 and SW3: units, tens and hundreds respectively.
Connecting, by means of SW5, Q1 base to pin 2 of IC6, we obtain after a 64 times division, the same frequency set by thumbswheel switches with quartz precision, and no need for a scale indicator.
Volume regulation of the pitch generator is obtained trimming resistor R5. In the same manner, with SW5 set to metronome, the small speaker reproduces the frequency set by thumbswheel switches but divided by 3840, thus obtaining beats per minute ratio