Generates a square wave pulse.
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To calibrate the Blue Ring Tester, adjust the R19 sensitivity potentiometer until the first two LEDs (or the first red one) just barely illuminate with the test leads open. blue ring tester schematic diagram exclusive
Note: Ensure the component is removed from the circuit, or at least one side is disconnected to avoid false readings from parallel capacitors. All LEDs lit (or 4-5 LEDs): The coil is good. No LEDs / 1-2 LEDs: The coil is bad (shorted turns). Why This Tool is Essential (Exclusive Insights)
low-power CMOS timer) to generate the initial excitation pulse. Threshold Detection: Generates a square wave pulse
| | Component Description | Quantity | | :--- | :--- | :--- | | IC1 | LM393 Dual Comparator (or 1/2 LM358) | 1 | | IC2 | CD4015 Dual 4-Stage Shift Register | 1 | | Q1, Q2 | General-purpose transistors (e.g., BC547, BC557) | 2 | | D1-D8 | LEDs: 3 Green, 2 Yellow, 3 Red | 8 | | C1, C2 | Ceramic capacitors (values vary, e.g., 100nF) | 2 | | R1-R10, etc.| Resistors: 1/4W, values ranging from 100Ω to 1MΩ | ~15 | | R19 | Trimpot for calibration | 1 | | Misc. | Power Switch, 9V Battery Clip, Test Probes, PCB | - |
: The tester uses low voltage (approx. 600mV), meaning it will not detect high-voltage breakdowns that only occur when the device is fully powered. Where to Find Resources First, I need to search for core technical
: A detailed one-page PDF showing the sequential LED control circuit.
: This pulse excites the inductor, causing it to parallel-resonate with an internal capacitor inside the tester. This forms a temporary LC tank circuit.
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.
The wiring from the PCB to the test probes must be as short and thick as possible. Stray inductance in long test leads adds resistance and dampens the ringing effect prematurely.