Test a known good inductor (e.g., a 100uH choke). Slowly adjust R_Cal (the 50k trimmer) until the Green LED remains steady but the Yellow LED flickers occasionally. This is the "sweet spot" for detecting 1 shorted turn out of 100.
Below is a text-based schematic of the classic Blue Ring Tester. Components are arranged for clarity. blue ring tester schematic diagram exclusive
+9V DC
|
|
| R1
+--/\/\/--+----+----+
| 10k | | |
| | --- C2
| | --- 100nF
| | | |
| | GND |
| | |
| +--+--+ |
| | | |
| |/ Q1 | |
+-----| 2N3904 | |
| |\ | | |
| +---+ | |
| | | | |
| R2 | | |
| 1k | | |
| | | | |
| +---+ | |
| | | |
| +---+-----+
| |
| | R4
| +--/\/\/--+-----> Output to
| | 10k | Comparator/
| | | Microcontroller
| | --- C3
| | --- 1nF
| | |
| | GND
| |
| |
| | R5
| +--/\/\/--+
| 100k |
| --- C4
| --- 100pF
| |
| GND
|
+-----------> Test Coil (Lx)
(connected between
this point and GND)
Note: This is a simplified representation. An actual PCB layout includes additional filtering and protection. Test a known good inductor (e
Following the blue ring tester schematic diagram exclusive above, trace the signal path: Note: This is a simplified representation
Do not test a coil. With probes open (air core), the tester should show maximum ringing (Green LED). If it doesn't, your threshold comparator resistors are too sensitive.
After assembly, do not connect a coil yet.
Connect a known good 10µH to 1mH inductor. The green LED should illuminate steadily. Short one turn of wire around the core. The red LED should now light.