Circuit: DIY Compact Isolated Oscilloscope Probe

Do you need an isolated connection to an oscilloscope? You can buy a solution, or you can DIY! If you are thinking about the latter, check out this "retro" isolated oscilloscope probe project.

Oscilloscope Probe Circuit & PCB

You can always log on to the Internet and have an electronic component or solution shipped to your door. But it's often more fun and more educational to build the solution yourself. Many of the projects that have appeared in ElektorMag over the years were developed for such reasons. For instance, a few years ago, Elektor author Erik Lins designed and wrote about a practical isolated oscilloscope probe. Refer to the nearby schematic. 
  As Lins explained, the ADuM5242 (U1) generates the electrically isolated voltages 5 V (VCCiso) and 0 V (GNDiso) for the input side. The two electrically isolated digital channels are taken to a three-pin connector strip, CON5. The supply for the AMC1200 (U2) is fed via a small choke that smooths the output voltage of the ADuM5242 a little more.
  "Using modern, low-cost components, it’s easy to construct a simple isolation amplifier for oscilloscope probes," Lins explained. "The restricted analog bandwidth does admittedly restrict the potential applications, meaning that it’s not feasible to measure, for example, the signal quality of differential high-speed signals (such as LVDS, USB or Ethernet). On the other hand, the true electrical isolation provided can occasionally be advantageous for connecting expensive differential probes, if the signal/offset relationship is of importance or when avoiding ground loops is a priority. The modest cost means you can also make several units of this circuit and equip every channel of your scope with electrical isolation. This isolation is provided not merely for the device under test, as could also be achieved with an isolating transformer; doing it this way, every channel is isolated from each other. Consequently, you can take potential-free measurements at different points in a circuit with just one single oscilloscope."

More About the Scope Probe

The Elektor article (130297) associated with this scope probe project appeared in the September 2014 edition of Elektor. Elektor Members receive ElektorMag, an Elektor Store discount, and full access to Elektor’s comprehensive online library, which includes this article and hundreds of others. Take out a membership today!