LED Stepper Tester v1.0
Here is a useful diagnostic device that you can plug in in place of a stepper motor to test your RepRap controller boards. It is very simple to solder up on an old offcut of stripboard, or you can get a proper little board from the RRRF.
It consists of two green and two red LEDs (though the colour scheme is up to you) wired back to back with current limiting resistors. As the L298N (U2) steps the motor the polarity sent to its two coils changes in sequence. If you plug this device in to the stepper connector and use the Step + and Step - buttons on the control window you can see this happening. It works because of the convenient fact that the LEDs don't blow up if you put them in the wrong way round, they just won't glow.
- Both LEDs off: all L298N outputs at ground.
- Red: this output goes + -.
- Green: this output goes - +.
For those of you needing more precise instructions, here are close-up photos taken by someone who constructed one from red LEDs (click to enlarge):