HYDRAmeter Reimagines DMMs as Open Source, Customizable Tools

The digital multimeter (DMM) is a ubiquitous tool found in every electronics lab, toolbox, or travel bag. However, most are static, unmodifiable devices. To address these limitations, John Duffy developed and built the remarkable open source HYDRAmeter, a DMM that stands out with its upgradeable design and enhanced usability features.

HYDRAmeter's primary microcontroller is a Raspberry Pi RP2040 on a Pi Pico board. The measurement front-end uses a Microchip MCP6S28 programmable gain amplifier in front of a Microchip MCP3461R 16-bit analog-to-digital converter. Together, Duffy hopes to add the capability of simultaneously measuring voltage and current to calculate a device's power consumption.

Duffy had several usability goals for HYDRAmeter to provide an improvement when compared to existing commercial options. For example, most DMMs have on-screen indicators, menus, or multi-function buttons to select or toggle features like AC or DC measurements. Instead of following that convention, Duffy gave HYDRAmeter an array of toggle switches. These multi-position buttons make it easy to change the functions and see the current settings at a glance. An added bonus of this approach is that more space on the display is available for non-static information.

A graphic LCD provides the readouts with physically large numbers. Duffy spent significant time reviewing and designing fonts that maximized readability. The detachable display is one of HYDRAmeter’s most unique features. Duffy opted for nRF24 radios instead of Bluetooth for reduced power consumption. This feature means easily and quickly placing the display somewhere in your eye line while putting the measurement unit closer to the device under test.

HYDRAmeter has several input options. Along the bottom are the familiar four-millimeter banana jacks found on traditional DMMs (and power supplies). Duffy also added a modular plug for upgradability. Currently, an XT-60 module is available. These DC connectors are typical for connecting batteries in remote-controlled vehicles like drones. Duffy targeted HYDRAmeters voltage of 60V and current of 30A for the XT-60 port. These specs make the meter suitable for characterizing 12S battery packs.

The open source project is an active work in progress. The HYDRAmeter GitHub repository has the KiCad Design, PCB gerbers, and firmware files. Duffy continues to refine the circuit board, so check the project log for the latest changes.