Current measurement probes for scopes from DC to some kHz are not new but still rather expensive. Therefore I had the idea of developing my own probe but I wanted to use an GMR (giant magnetic resistance) based sensor for it. I still had an KMZ51 in my lab and therefore I started development with this component.
This sensor includes a bridge of field depending resistors and two additional coils. The flip coil is needed for degaussing the sensor and the compensation coil can be used for zeroing out external influences like the geomagnetic field.
Creation of the degaussing pulses and automatic zeroing are done by a small ATTiny13 micro-controller. This process starts automatically at power on or on demand by pressing a key. A red LED is on as long as the zeroing process is ongoing and gets off if successful.
Please have a look to the documents, attached to this project. The LabNotes document describes all development steps from the beginning up to now including diagrams and measurement results. The 3D Model document includes my current mechanical solution for a spring loaded clamp including sensor and ferrite yoke. A set of hand milled parts is already finished. The circuit diagram will always be updated to the most recent version if anything changes.
One instrument is completely assembled using final PCBs from Elektor PCB service and it is working well. From my perspective, the project is finished.