Here is a dandy two-transistor metronome which you can build into a small
plastic case. You can use an old nonworking transistor radio to house this
gadget. In most case you can merely remove the main circuitry but retain
some parts, such as the on-otf volume control potentiometer, speaker and
battery holder. lf you have done this, you have just eliminated the following
items: SPKR, 51, and 81.
The circuit can be powered with two orfourAA cells and drains about 10 mA.
As soon as 31 is closed, the metronorfle stbrtq clacking. By adjusting potentiometer P1 you find the "beat'or frequency of clacking you wish to set.
To calibrate, you have only to synchronize your metronome with a commercial
type or any known source.
Figure l shows the schematic diagram for the Mini-Metronome. At the heart
of the circuit are Q1 and Q2, as a two-stage direct-coupled amplifier, which
allows the circuit to generate intervalled pulses.
Figure 2shows a mechanicalview of the metronome, using a terminal strip
as "chassis" for the small components.
Position of the polarized components,uch as Gl, C2 and the transistor,
should be observed in the mounting.
Parts of Mini Metronome
Q1 - 8C548 NPN transistor
Q2 - 8C558 PNP transistor
51 - SPST toggle or slide switch
81 - 3V or 6V - two or four AA cells
SPKR - 4 or I ohm, 2 to 4-inch loudspeaker
P1 - 1,000,000 ohm Potentiometer
Rl - 10,000 ohm, 1l4W,5olo resistor
PA - 1,000 ohm, 114W,5% resistor
C1 - 10 pf, 6 VVVDC electrolytic capacitor
C2 - 10 Uf, 6 WVDC electrolytic capacitor
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