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The most important debugging tool in any E.E.'s toolbox is a trusty multimeter. A multimeter can measure continuity, resistance, voltage and sometimes even current, capacitance, temperature, etc. It's a swiss army knife for geeks!

You should go through all of these sections in order, as they build on each other.

• Continuity measurements
  How to tell if two points are electrically connected
• Resistance measurements
  How to measure resistance - resistors, potentiometers and sensors
• Voltage measurements
  How to measure voltage - battery testing, wall-wart adaptor testing, and the terror of mixed AC/DC measurements.

Everyone always asks What multimeter should I get?

Well, since they're rather commodified (there are dozens of manufacturers) it is hard to make everyone use the same model, even though it would make things easier.

These are the necessities:

• Continuity testing with piezo buzzer
• Resistance test down to 10 ohm (or lower) and up to 1 Megaohm (or higher)
• DC voltage test down to 100mV (or lower) and up to 50V
• AC voltage test down to 1V and up to 400V (or 200V in the US/Canada/Japan)
• Diode testing

Here are nice things to have in your meter

• Auto-off - to keep from draining the batteries
• AC and DC current test, from 10mA to maybe 200mA and then also a 10A one as well
• Stand - a thing that flips out and keeps it upright on your table
• Auto-ranging - note: some people don't like auto-ranging because its slower and not as precise
• Hold - keep the maximum value on the screen so you can probe without looking at the meter.
• Common battery - such as 9V or AA's, pocket meters use hard-to-replace coin cells

These are things that I rarely (if ever) use, in decending order

• Frequency counter - before I had a scope this was surprisingly useful!
• Capacitance testing - usually to check random SMT caps
• Inductance testing - how often do you really use an inductor?
• Duty cycle - never used this
• Transistor beta meter - people don't really work with transistors anymore
• Temperature probe - I use the "Pease temperature test": a finger

I have a selection of suggested meters on this page, I strongly suggest the "better" (At $15 its a great value) or "best" ($50, autoranging, has a temp probe, all sorts of other junk) ones as the "good" one is really kinda bad. If you already have a multimeter then just use that one. I'll only be covering digital multimeters here so if you have an analog one, it may be a little different and you'll have to experiment to figure out what's up

A good multimeter will cost about $25. I suggest getting a ranging one , with current testing, and a wide range as well as easy-to-replace battery. You don't need to spend $200 on a Fluke 73! A $50 meter will be excellent. Auto-ranging meters may keep you from tripping up on ranges at first, but they're slower and often flakier.

I have had a Wavetek Meterman 27XT for half a dozen years and its been really good to me, but it was also about $80.

Here are many other links for learning how to use a multimeter

• TangentSoft's half-hour video tutorial
• Make Magazine's Bre & Joey Grand on how to use a multimeter
• Robot Platform tutorial on using digital multimeter