Linear scale Small size

40 to 208 beats per minute

Parts:

P1______100K   Linear Potentiometer

R1_______10K   1/2W Trimmer Cermet
R2_______10K   1/4W Resistor
R3______330K   1/4W Resistor
R4_______50K   1/2W Trimmer Cermet
R5______100K   1/4W Resistor
R6,R7_____1K   1/4W Resistor

C1________1µF   63V Polyester Capacitor
C2_______10nF   63V Polyester Capacitor
C3_______47µF   25V Electrolytic Capacitor

IC1_____NE555   General purpose timer IC

Q1,Q2___BC560   45V 100mA Low noise High gain PNP Transistors
Q3_____ZTX753   100V 2A PNP Transistor

SW1______SPST Switch (Ganged with P1)

SPK______8 Ohm 40mm. Loudspeaker

B1_____12V Battery (MN21, GP23A or VR22 type)

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Notes:

• Q1 & Q2 provide linear frequency operation of IC1 following P1 resistance variation.
• Q3 was added in order to obtain a louder click, similar to clockwork metronomes.
• 12V micro battery was used to obtain more output power and more compactness.
• Rotate P1 fully towards R2, then set R1 to obtain 40 beats per minute (compare with another metronome).
• Rotate P1 fully towards R3, then set R4 to obtain 208 beats per minute.
• Finally mark the entire scale with the usual metronome steps as following:
  40 - 42 - 44 - 46 - 48 - 50 - 52 - 54 - 58 - 60 - 63 - 66 - 69 - 72 - 76 - 80 - 84 - 88 - 92 - 96 - 100 - 104 - 108 - 112 - 116 - 120 - 126 - 132 - 138 - 144 - 152 - 160 - 168 - 176 - 184 - 192 - 200 - 208.