DIY Active Differential Probe for your oscilloscope | Do-it-yourself electronics

An active #differential #probe designed for the measurement and visualization of waveforms of mains voltage (or at mains' voltage level) on a common #oscilloscope without running the risk of frying the scope, the probe, or worst yourself!

In a previous video (here:    • Easy DIY passive #probe to measure #m...  ) I've showcased a passive probe, unlike that one this active probe uses only one input channel of the oscilloscope.

The probe run on a 9V battery that lasts about 20 hours (based on Duracell's data sheet calculated for the current drawn by the circuit.)
It features an input impedance greater than 4MΩ, an output impedance of ~50Ω and an attenuation ratio of x200 (200:1). The theoretical maximum input voltage is 800Vp (given by the voltage limit of the resistors used in the attenuator). This allows to take measurements not only on common 230/240Vrms but even at 380/400Vrms (used in Europe), including phase-to-phase on a three phases system.
BEWARE that if you try to make this project yourself you'll do it under your own sole responsibility, I'll take no liabilities! Keep in mind that the circuit's performance and limits heavily depends by the components used and how the circuit has been made. I mounted two of the four resistors of the attenuator on the PCB and has been covered with an insulating resin that is NOT visible in the pictures.

The probe is built around an LM4562 in IA configuration, and a resistive attenuator. Tests confirmed that there is no need for capacitive compensation since the input capacitance is remarkably low (less than 2pF) and the frequency range of interest is about mains frequency (50/60Hz) and its harmonics, so rarely there is the need to read frequencies above 20Khz.
I hadn't the possibility to test the probe for its actual bandwidth, though.

For the sake of simplicity I used common 1% resistors (with 20ppm/C) rated 250V. The "high" voltage must be well separated by the low voltage part. The key point of this probe is the link to ground, or PE (Protective Earth) that provides its safety. It works on both TT and TN systems. The PE is also carried by the oscilloscope, but the provision of a separate connection for grounding (the green banana socket) is important in the case of fault of the cable, the use of a battery powered oscilloscope and the case when the plug is disconnected from the scope.

This probe MUST NOT be used where the line is not protected by a GFCI, RCD or RCCB.

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