I saw one day an interesting looking multi-meter MUSTOOL MT77 Large Screen Smart Digital Multimeter Voltage Tester 3-Line Display Fully Auto-Range True RMS 6000 Counts DMM with Analog Bargraph.It is advertised as phone size design: 12 mm thin body and pocket size design make it looks like a smartphone. The meter has unibody design so no need to plug in and out probes because wires are fixed to the case (that has it’s pros and cons but on quite cheap multi-meters I consider it to be OK design choice). The pricing seemed reasonable at list price around $15, was on sale around $12.
It was also advertised as having an interesting Automatic Identification Design: Automatic identification design allows for no-switching when testing AC/DC voltage, Hz, continuity and resistance. The meter also promised a large screen triple line display can show 3 test results on the screen, such as voltage, frequency and analog bar.
DC voltage measuring worked well and was pretty accurate to 0.1V resolution.
AC voltage measuring also worked when you just put the measurement probes to voltage source.
I tested the resistance / continuity testing functionality. It worked but it was a little bit annoying slow. I am used to get the beep on continuity testing immediately and after few seconds…
Electrical field measurement seemed to indicate nearby mains electrical wiring well.
The V-ALERT is a buzzer that sounds when NEAR a voltage, without needing actual contact by a probe. Hold the unit near a power line, it will buzz, more buzz and bigger bar on display means higher voltage. The meter has also LIVE mode that allows to determine which lead is HOT and which is ground on mains wiring, by touching the the wire to be tested with at least one probe.
On the back side of the meter there is a LED lamp that is a nice addition to features.
For most measurements you use the AUTO mode that the meter is automatically set when power is turned on. AUTO is the setting for actual use of the probes across a voltage. If the meter sees voltage between the probes, it will determine if there is AC or DC and show the voltage. The meter also shows the voltage on bar-graph. For AC the meter shows also shows the frequency (40-1000 Hz).
If there is no voltage, the meter tries to read resistance. The meter promises to show the resistance value in 1 ohms to 6000 ohms range. If the resistance is below 30 ohms, the CONTINUITY buzzer sounds as well. The buzzer and resistance measurements seem to take more time than voltage measurements.
Those basic functions worked OK, but the next question is the accuracy and how the automatic mode detection actually works.
Some small testing shows that if there is DC more than around +-0.3V the meter measures DC. If there is AC component more than around 2V then the meter measures AC voltage and frequency. I have not figured out the exactly how meter always works when there is both AC and DC on the incoming signal. When voltage between pins below those tries to measure resistance in 1-6000 ohms range. This can be confusing when measuring for example very flat battery, instead of zero volts you can start getting strange resistance values on screen.
The measurement accuracy was OK considering that the voltage measurements had only just one range with 0.1V resolution. My tests with DC and AC gave accurate reading I expected to get. I used my other multi-meter and my reference meters as reference for voltage accuracy.
I was not happy with the resistance measurements. The resolution is one ohm. The measurement feels very slow, especially it takes annoying long time for beeper to react to low resistance. The measurement accuracy especially at the low resistance range was bad. When I measured 3.8 ohms resistor, I got reading zero ohms. When I measured 38 ohms resistor, I got 24-25 ohms reading. Those are quite much off. When I measured 5.1 kohms resistor, I got 5 kohms reading, which is reasonably close.
- Small size that fits nicely to pocket with the wires
- Large easy to read display with bargraph
- Can show AC voltage and frequency at the same time
- Quite stylish and Good looking as it looks like a smartphone when it sticks out of your pocket.
- OK accuracy for basic AC and DC measurements
- Built in LED lamp
- Built in contact-less voltage detector
- OK safety ratings at least printed to meter
- Inaccurate resistance measurement mode
- Resistance measurement is slow
- Continuity beeper is annoyingly slow to act
- The automatic measurement mode acting is sometimes annoying
- Has only has one range for Volts (up to 600V in 0.1V steps)
- Only one range for ohms (up to 6000 Ohms in 1-Ohm steps)
- The technical data on product page is not accurate
The end verdict that that the MUSTOOL MT77 multi-meter is overall overall disappointing. A not so smart “Smart Meter”. It was promising, but did it feels like it got only half way to being good on the actual implementation (would their newer model MUSTOOL MT99 have improved from that?).