Hear Those Ohms: An Audible Multimeter for the Blind

A friend recently had a speaking multimeter fail on him, a relic from the olden days when Radio Shack (remember them?) sold neat stuff. Being blind, it was not just a curiosity, but a vital tool for taking electrical measurements.

Fortunately, he had heard about some work using Arduinos to read display data from specific multimeters, as discussed here. In that project, they grabbed the RS232 data output from the meter and converted it into audio.

So I built one, with a few changes, of course:

  • I wanted a simpler (less custom) design, so I opted for the Adafruit Wave shield, which plays audio on a SD card. This made the playback very simple.
  • Of the two ‘lower-end’ meters considered likely to work with this (Digitek’s DT-4000ZC and TP4000ZC) I was able to get the Digitek with a USB connector, not an RS232 port (which would require an RS232-to-USB adapter from eBay as well).
  • Because I could connect directly via USB, it was straightforward to write a VB.net program to read the port and test out the audio. This let Oriano pick the features that worked best, and let me try out some usability ideas (like press to announce, and press and hold to announce repeatedly).
  • For packaging, I ended up with a large project box, almost as large as the meter itself. For that, I turned to the poor man’s 3D printing, balsa wood and JB Weld, and carved a couple of inserts to keep everything in its place without shifting. That and a judicious use of corrugated plastic sheeting, and I even had a battery holder.

The end result is a nice black ‘brick’ which announces the meter settings depending on whether you press (one time announce) or press/hold the button (repeated announcing). Simply plug in headphones (or a powered speaker) and get audio updates of readings – which is handy not just for the blind, but for anyone needing their eyes somewhere else other than on the meter display…

Note: part 2 continues with more construction details.

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