The LM3914 is a 10-step dot/bar display driver. It compares the input voltage (pin 5) to a reference voltage set between pins 7 (Ref Low) and 8 (Ref High). In the Blue Ring Tester, the reference is set so that the input voltage from the decaying ring crosses each threshold in sequence.
Blue Ring Tester is a specialized diagnostic tool used primarily for testing high-Q inductive components, such as flyback transformers (FBT) switched-mode power supply (SMPS) Blue Ring Tester Schematic Diagram
The "Blue Ring Tester" gets its name from the characteristic blue color of the original PCB and the "ringing" waveform it produces. Unlike a conventional LC meter or multimeter, it injects a short, sharp voltage pulse into the coil under test. If the coil has no shorted turns, it will "ring"—producing a decaying sinusoidal oscillation. If there are shorted turns, the energy is dissipated instantly, and the oscillation dampens almost immediately. The LM3914 is a 10-step dot/bar display driver
Should I help you find for this specific electronic project? Blue Ring Tester is a specialized diagnostic tool
When the 555 output goes HIGH:
While various manufacturers produce "Blue Ring Testers," the underlying schematic diagram almost universally derives from classic pulse-testing circuits popularized in electronics magazines and open-source forums. The diagram can be broken down into three functional blocks: