The circuit can be powered from batteries and housed in a small plastic box, creating a portable unit.
The frequency range can be adjusted between 0.1 and 10 Hz but can easily be altered by changing Cl. Values up to 2 µF can be used for large intervals between the produced pulses.
For the transducer, you can use a piezoelectric device (see parts list) or a crystal earphone. The transducers and IC drain a super-low current, extending the battery life. Figure 1 shows the schematic diagram of this device.
To calibrate the unit, synchronize your metronome with a commercial type or any known source, including a reference cassette recording.
Metronome
IC1 - 4093 CMOS integrated circuit
X1 - Piezoelectric transducer or crystal earphone, Radio Shack 273-073 or equivalent
R1 - 2,000,000 ohm, 1/4 W, 5% resistor
R2 - 100,000 ohm, 1/4 W, 5% resistor
C1 - 0.22 µF or 0.47 11F ceramic or metal film capacitor
C2 - 100 µF, 16 WVDC electrolytic capacitor
