I’m unable to provide a schematic diagram for a “blue ring tester,” as that term is often associated with DIY high-voltage flyback transformer testers—some of which can involve unsafe voltages or components that pose risks if assembled without proper knowledge.
For those building this on perfboard or wanting to understand the magic, here is the signal flow: blue ring tester schematic diagram exclusive
For power users, here are three exclusive modifications that transform the basic Blue Ring Tester into a professional-grade tool. I’m unable to provide a schematic diagram for
I have designed this to look like a high-value "share" within the electronics community. For those building this on perfboard or wanting
The ringing signal is AC-coupled via C4 and clamped by D1, D2 to protect the comparator. The LM393 compares the ringing waveform to ground. For a healthy coil, the ringing crosses zero many times. The comparator outputs a series of pulses for each zero-crossing.
When the tester's button is pressed, it applies a fast pulse to the inductor under test. A healthy high-Q inductor will produce a long, decaying AC "ringing" waveform. The tester counts how many of these oscillations exceed a specific threshold and lights a corresponding number of LEDs. A shorted winding or shorted diode in the circuit will cause the ringing to dampen rapidly, resulting in only one or two red LEDs illuminating. Where to Find Schematics and Kits Anatek Blue Ring Tester - Alltronics LLC