Kindly Morrow
4000-Count TRMS Auto-Range Digital Multimeter
Diagnose switching supplies, PWM circuits, and motor drivers with readings that are actually correct. True RMS measurement means the meter calculates real waveform power instead of assuming a clean sine and scaling from there. The difference shows up every time you probe something that isn't a wall outlet.
The 4000-count display gives enough resolution to catch a 3.28V rail sagging under load versus a healthy 3.30V. Auto-range gets you a reading fast. Manual range locks the input for a faster refresh when you already know the ballpark. Built for bench work, but rated and sized for field use.
Things to build with this
- Tune ESP32 deep sleep firmware by running the meter in DC microamp mode with a series shunt resistor in the power rail. Read actual sleep current draw, adjust wake intervals, and project real coin cell runtime from measured numbers instead of datasheet estimates.
- Catch ripple on a 12V PSU feeding a CNC controller by switching to TRMS AC mode while the supply is under load. A non-TRMS meter underreports ripple on switch-mode supplies. This one won't, so you'll see whether the cap bank is actually failing.
- Map cold solder joints on a freshly assembled PCB revision using resistance mode with the continuity beep. Probe each net from pad to pad before powering the board, and flag any joint reading above a few ohms before it causes an intermittent fault under thermal stress.
Key Features
- TRMS measurement: accurate on non-sinusoidal waveforms including PWM, motor drivers, and switching regulators
- 4000-count display: resolves down to 1mV on the 4V range, enough to catch subtle rail sag
- AC/DC voltage: measures up to 1000V with CAT III/CAT IV rated input protection (verify on unit label)
- Auto-range and manual range: switchable, manual locks range for faster display refresh
- Resistance measurement with audible continuity beep for tracing PCB nets quickly
- DC current mode: supports shunt-based current measurement for low-power circuit diagnostics
- Ships from US warehouse, in stock
Frequently Asked Questions
What does TRMS actually mean and when does it matter?
True RMS meters compute the real power content of a waveform by integrating the full wave shape. A non-TRMS meter assumes a perfect sine and scales from the peak, which gives you the right answer on mains voltage and the wrong answer on everything else. PWM signals, motor drivers, switching regulators, and class D amplifiers all produce non-sinusoidal waveforms. On those circuits, only a TRMS meter gives you a trustworthy reading.
When should I use auto-range versus manual range?
Auto-range picks the correct measurement range on its own, which is faster for general probing when you don't know the expected value. Manual range locks to a specific range and typically updates the display faster, which is useful when you're watching a value in real time or already know the voltage ballpark and want snappier response.
Is this safe to use on mains voltage?
The meter measures up to 1000V AC/DC. Before working on mains or any fixed installation wiring, check the CAT rating printed on the unit label. CAT III covers fixed installation wiring like breaker panels. CAT IV covers utility entry points and outdoor wiring. Your probes need to match the same CAT rating as the meter, not just the meter alone.
Can I measure current draw with this, or just voltage?
Yes. Use DC current mode with the correct input terminal (not the voltage input) and the appropriate current range. For very low current measurement on battery-powered projects, put a known shunt resistor in series with the load and measure the voltage drop across it, then calculate current from Ohm's law. Always check the input range limits and fuse rating in the datasheet before measuring anything near the maximum current range.
Why we stock this
Curated by Kindly Morrow. We test and vet every product before it hits the store. If we wouldn't use it in our own builds, we don't sell it.
Things to build with this
Fun projects to try once you get your hands on it.
Connect it to Home Assistant
Most hardware plays nice with Home Assistant. Add it to your dashboard, write an automation, and make your home a little smarter.
Hook it up to Claude
Wire it to an API, point it at Claude, and let AI decide what it does. The future of hardware is firmware you didn't write.
Give it to a kid and watch what happens
Half the fun of hardware is watching someone else figure it out. No instructions, just vibes.
