Key technologies: USB, isolated power supplies, high-voltage safety
In 2011, my brother and I looked at buying some electronics equipment but were disappointed at the high cost of multimeters and oscilloscopes. We wanted a USB-connected multimeter with some oscilloscope capabilities. After some research, we didn’t find any of these available online, so we decided to build our own.
We designed a board that could measure voltage, current, and resistance. We supported measurements up to 1000 Volts, 10 Amps, and 10 megOhms. We designed the system to be software-controlled ranging with full auto-ranging support. The system connected to the PC via USB and was powered by USB.
Safety considerations were a large part of the design. We separated the communications and control section of the board from the analog section with an isolated DC/DC converter. The analog section used large trace spacings to give adequate creepage/clearance distance. Optocouplers were used everywhere that data needed to be transferred between the isolated and the control sections of the board.
The USB communication was handled through a USB CDC emulator and corresponding driver on the PC. The EETool appears on the PC as a serial device. I wrote a simple shell to parse commands and display data.
The system worked and we were able to take measurements. My brother used the multimeter on a school project when he needed to capture some circuit transient response curves.