Step 2: Test the SD Interrupter

Power on the interrupter. Depending on whether or not you have a micro SD card installed, you should be greeted with either “Fixed Mode” or “No SD card found” on the display. Press [Down] until you see “Fixed Mode”, then press [Select] to launch fixed mode. Look into the optical transmitter and verify that you see a blinking red light. If you do, hooray, your interrupter works! Proceed to step 3.


If no display is present...

  • Make sure all ICs are correctly installed in their sockets.
  • Measure the voltage between pins 7 and 8 of the ATMega328 and confirm that it is 5 volts. If it is not, check for soldering errors around the 78L05 regulator and the pins of the ATMega328.
  • Make sure R1 and R9 are not switched. Swapping R1 and R9 will cause extremely low contrast on the screen.
  • Try switching on the backlight. In bright lighting conditions the screen may be hard to see without a backlight.


If no backlight is present...

Lack of a backlight indicates that the 5V rail is absent. Check for shorts on the board. Verify that the batteries are installed in the correct orientation.


If the display is present but the LED does not light...

  • Check the soldering of R3 and the fiber transmitter.
  • Check the ATMega328, particularly pin 4.
  • Confirm that the fiber transmitter is not mechanically damaged.


If the buttons don’t work...

Check the soldering of the buttons and the 1K resistors next to them. Be gentle with the buttons, as they are tall and too much sideways force will damage them.



Testing that the basic interrupter functionality works will let you test your coil. If you want to do more advanced troubleshooting go to step 17.


SD interrupter controls


Need help?

If you encounter a problem that isn’t covered here, take a look at our online help forum. Someone else may have had the same problem and figured out a solution.

Please post on the forum rather than emailing us for support, so that everyone can learn from how you resolved your problem!



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