A few words from the books: A distinctive feature of electronic measurements is the multiplicity of the quantities and the wide ranges of the values measured. In measuring the parameters of electronic equipment, it is often necessary to use indirect methods, requiring the use not only of measuring instruments but also of auxiliary apparatus, such as generators for voltage and current at various frequencies, operating in a continuous mode or with different types of oscillation modulation. (Momot, E. G. Radiotekhnicheskie izmereniia. Moscow-Leningrad, 1957.) There is a saying that you can judge about the craftsman by his instruments.
To develop your own projects, or to repair electronic devices, you will need: Oscilloscope - the most versatile instrument. It will help you actually see the form of the signals, changing with the time. Modern Digital Storing Oscilloscopes offer great functionality at a really good prices. If these are your first steps in electronics, though, do not be discouraged by its price. EDI will give you cheap solutions how to monitor signals. Still, sooner or later, you will buy one. Tip! An old trick will help you when you measure fast changing signals. Older oscilloscopes, as well as the cheap ones, have relatively high input capacitance – 30pF to 50pF. This will distort the high frequency signal. The solution is to use the oscilloscope probe at 10x and increase the oscilloscope gain. Digital Multimeter - its name says it – it measures lots of properties – Voltage, Current, Resistance, Capacitance, Temperature, Transistor’s gain. Digital Multimeters are intuitive to use and come in a great variety. The following tips might be helpful. Voltage - If you are not sure what range to use, start from the highest one. All instruments have an input protection, but better safe, than sorry. If you do not have a special probe, avoid measurement of a high voltage impulse signals – for example in a switched-mode power supply. Current – Usually the range of 200 mA is fused, so if you measure higher current, the fuse will burn. If you measure currents of 2 to 20A range, be sure to do it fast (5-10 seconds), or you will melt down the probes and/or the instrument. Duty cycle - Assuming that you do not have an oscilloscope, old trick will help you to measure the duty cycle of a digital (rectangular waveform) signal with a known amplitude using a digital multimeter. Measure the voltage of the pin you know that has rectangular waveform output with a known amplitude. Let assume we get a reading +3.3V and the signal amplitude is 6V. Divide this result with the amplitude (3.3/6=0.55) and you will get the duty cycle of the measured signal.This method is good enough for frequencies between 10Hz and 500kHz. Transistors – If your Multimeter does not have a transistor measurement section, you can still tell which terminal is which. Turn resistance measurement on (if you do not have a special area for PN junction, use 200 to 2000 Ohm) For NPN transistor, connect the positive probe (the red one) to some of the transistor's terminals and repeatedly measure other two. When you get close readings, the positive probe shows Base, the terminal with less resistance is Collector and third one – Emitter. For PNP transistor you do the same, only the negative probe shows Base Capacitors – A very important issue with capacitors is the Equivalent Series Resistance. Wiki info Big ESR values may cause modern Switch Mode Power Supplies to malfunction, can generate heat or perform bad in audio/video analog circuits.Sometimes a defected capacitor is easy located - it is swollen and the electrolyte leaks. In other cases, you have to chek it with a ESR meter. Signal Generator – It provides a known signal form, with an appropriate level and frequency, so you can test elements, modules or ready devices. Each time you measure some electrical circuit, its electric properties – resistance, impedance, capacitance – change, depending on the measurement instruments. Each time you make any electronic measurement, PLEASE, REMEMBER, that the electricity may be hazardous!