4 is better. Do not buy an analog storage scope in order to learn about oscilloscopes, because these are much harder to use. Get as much scope as you can afford; like good books, good tools are cheap if you use them.

POWER SUPPLY

A power supply (aka bench supply) provides “ known-good” power to your circuit. After we figure out how much power our circuit actually needs, we can then decide how to power it for regular use, like with batteries or a wall wart.

Bench supplies let you adjust the output voltage, which is good for initial testing: while slowly increasing the voltage to your circuit’s operating value, you can look for burning components, smoke, arcing, explosions, etc. The fanciest supplies also have current limiting, which sets the maximum amount of current the circuit is allowed to draw. A circuit that draws way too much current could be cooking itself, or might have a power short to ground — maybe through that screwdriver you left under the PC board. Some power supplies also have meters that show voltage and current.

Many circuits require both positive and negative DC voltages. To test these, you need a dual-output supply, which has separate V+, V-, and ground terminals. Expect to spend a minimum of $50 for a good supply, more if you want dual output and meters.

MULTIMETER

A multimeter measures the voltages and currents in a circuit, as well as the characteristics of individual components such as resistors and diodes. They all measure resistor values (ohms), but try to find one that can also measure capacitance (microfarads), since it is sometimes difficult to read the values on capacitors.

Use a multimeter to “ohm out” an unknown circuit. This means tracing out the connections on a circuit board to see what is connected to what, so that you can create a schematic drawing that shows all the circuit’s connections.

Multimeters are designed to withstand wide ranges of inputs, so you can use one to check for high voltages in unknown circuits. The terms volt-ohm meter (VOM), multimeter, ohmmeter, and voltmeter all refer to pretty much the same thing. Expect to spend a minimum of $10 for a handheld voltmeter,

or $50 for one with capacitance ranges.

FUNCTION GENERATOR

A function generator injects a regular signal at a selectable frequency into a circuit. In certain circumstances you can do this with a CD player or other gear, but a function generator is more flexible. Look for one that can generate sine waves (handy for testing audio circuits), square waves (handy for testing filters, amplifiers, and digital circuits), and triangle or sawtooth waves (handy for graphing circuit behavior). More costly units can produce any waveform shape you want; these are called programmable waveform function generators or arbitrary waveform generators. Expect to spend $75–$500, or more for ones that can generate arbitrary waveforms, or go up to higher frequencies.

HOW TO USE AN OSCILLOSCOPE

The oscilloscope draws a graph of voltage versus time on the display screen (known as a graticule to old-timers). By connecting probes to your circuit and generating these scope traces, you can see what’s going on.

Don’t be intimidated by the large number of knobs and buttons. These controls are grouped into 3 basic function areas: timebase, sensitivity, and trigger. Timebase and sensitivity controls change the graph’s appearance, setting the horizontal and vertical axes, respectively. Trigger controls tell the oscilloscope when to start drawing the trace. Here’s how to operate each control area.

Timebase — Adjust the Horizontal Find the biggest knob on the front of the scope, and “ratch” it around clockwise and counterclockwise. This is the horizontal scale adjustment, and it determines the time represented by each grid line (or “division”) on the display. A typical range is from 100 nanoseconds to 1 second per division. At the short end of this scale, the trace zips left to right so fast on the display that all you see is the line left behind. At the long end, the trace appears as a traveling dot. At any setting, the trace starts at trigger time, which you can think of as time=0.

Sensitivity — Adjust the Vertical Most scopes have multiple channels, which plot separately to the display. Each channel corresponds to its own electrical input, usually a BNC connector

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