When is a Multimeter Not Enough?

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A digital multimeter, or DMM,  is a great tool for debugging many types of electrical circuits. It is my first choice when experiencing a problem with my electrical projects. However sometimes a DMM is insufficient to show the root cause of a problem.

When a DMM is unable to solve a problem, there are several different types of tools that I can turn to depending on the problem. These tools include Oscilloscopes, Function Generators, Logic Analyzers, and Network Analyzers, which are all the next step up from a DMM. Luckily, all of these tools are built into the Analog Discovery 2 and WaveForms 2015!

waveformsTools

Some examples of when a DMM fails to assist in debugging usually include rapidly fluctuating signals, and this includes the following situations:

Clocked Signals

There are many instances when I want to check a microcontroller timer period or the clock of an FPGA. To simulate this, I use the Function Generator in Waveforms 2015 to create a square wave at 50 Hz.

When trying with the multimeter, it refused to show the oscillation of the signal.

square_wave

However the Oscilloscope in Waveforms 2015 has no problem showing the square wave!

Bus Protocols

Ensuring that serial communication is working properly can be difficult without the correct tools.

This time the multimeter tries to help by giving the average voltage of the serial line based on the number of bits set high. While the attempt is appreciated, it’s not quite as useful as a Logic Analyzer.

UART_dmm

The Logic Analyzer in Waveforms 2015 gives the actual waveform received by the Analog Discovery 2, as well as an interpretation of the bits in a human readable format.

uart_logic_analyzer

Debugging/Verifying Filters

When designing filters, it is nice to be able to verify that the cutoff frequency is as designed. The standard test is to use a Function Generator and an Oscilloscope to slowly increase the input frequency and observe the output. For this task, the multimeter once again refuses to help…

hightpass_dmm

But the Network Analyzer in Waveforms 2015, on the other hand, has no trouble giving the Bode plot of the filter.

In conclusion, while a DMM is great for checking continuity, DC voltages, currents, resistance, and sometimes even capacitance, oftentimes a DMM is not sufficient for successfully finding the cause of an electrical problem. My go-to tool for quickly debugging a simple circuit is still a DMM, but when it comes to problems that require a little more, or something other than what I mentioned above the Analog Discovery is my first choice.

If you are interested in learning more about the Analog Discovery 2, take a look at either the reference page or the Analog Discovery 2 Quick Start videos.

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