Repurposing Moving Coil Meters To Monitor Server Performance

Snazzy analog meters can lend a retro flair to almost any project, but these days they often seem to be retasked as indicators for completely different purposes than originally intended. That’s true for these Vu meters repurposed as gauges for a Raspberry Pi server, and we think the build log is as informative as the finished product is good-looking.

As [MrWunderbar] admits, the dancing needles of moving-coil meters lend hipster cred to a project, but getting his Vu meters to cooperate and display network utilization and disk I/O on his Raspberry Pi NAS server was no mean feat. His build log is full of nice details on how to measure the internal resistance of the meter and determine a proper series resistor. He also has a lengthy discussion of the relative merits of driving the meters using a PWM signal or using a DAC; in the end, [MrWunderbar] chose to go the DAC route, and the video below shows the desired rapid but smooth swings as disk and network usage change. He also goes into great depth on pulling usage parameters from psutil and parsing the results for display on the meters.

Looking for more analog meter goodness? We saw a similar CPU load meter a few months back, and there was this mash-up of Nixies and old meters for a solar energy CEO’s desk.

[via r/raspberry_pi]

11 thoughts on “Repurposing Moving Coil Meters To Monitor Server Performance

  1. the scale (-20…+5) isn’t really intuitive, a simple piece of printed paper could make it much more understandable. Perhaps with some colors of green orange and red. Just a thought.

    1. Agreed, it looks indistinguishable from stepper drive gauges. IMHO the draw of analogue gauges is their inherent damping that smooths out a noisy signal and gives them their mechanical feel.

      I think the acceleration also needs to be biased in the positive direction – needle rises smooth but fast, and has a natural decay rate when decreasing, rather than being ‘driven’.

      The other thing is these feel distinctly ‘digital’, like they are being driven on a common clock, due to their rapid and regular movements, and that totally upsets the analogue feel. I think a longer sampling period combined with those other suggestions would probably also result in a better kinematic.

    2. +1 on ‘missing analogue feel’

      Stepped = digital feel.

      But cheep meters/circuits had that delayed and sometimes variable rise/fall rate, or input was smoothed by too large a cap. Higher quality devices/meters had a very fast response (15″ high-end tape decks), as you see these meters respond to a stepped input.

      The other issues with the super fast stepped movements, is eye strain. Those super fast movements are a no-no. Your eye will try to keep up with the movement. The start and stop is too abrupt. Can cause eye and mental fatigue. After a while, some people experience pain.

      Adding a moving average would make a huge improvement in both reducing or eliminating eye strain, and in proving more of an analogue feel.

      Instead of the SMA (Simple Moving Average), I’d suggest using the Linear Weighted Moving Average and with a short period; try 3 to 10 to start. Smoothed, but responsive. Even an EMA would be worthwhile.

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