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Fig. 1.51: Acoustic panel
1.2.4 Moving-coil instrument
A moving-coil instrument is fragile and easily damaged by higher voltage or current. If you do your own
experiments, make sure that you always have a sufficiently sized series resistor installed. We use a 9V block
battery in our experiments, a series resistor of 4.7 kΩ is thus sufficient. Where current is measured, a suffi-
ciently sized resistor should be connected in parallel. To be on the safe side, start with 10 Ω. Thus, currents
up to about 100 mA will not impact the moving- coil instrument at all.
1.2.5 Practical use of the circuits in home and garden
If you are keen to make use of your favourite circuit, build it on a stripboard rather than a breadboard.
Components and connections are then soldered together. This ensures that these durable connections work
properly over a long time. The soldered connection to the stripboard ensures mechanical stability. Power is
conveniently supplied by a 9 V block battery. You could also use a commercial power adapter, but it should
feature all relevant safety labels – not just the CE mark. Whatever the case, the circuit should be installed
into a suitable case. A watertight housing is essential for outdoor use.
1.2.6 Buttons and switches
Switches and buttons are often needed in electronics. Our experiment box contains no such components.
Where necessary, they are realized by means of jumper wires, where only one wire end is inserted. By
momentarily inserting the other wire we can simulate a button; by alternately inserting the wire into two
different positions, it will act like a switch.
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