What you will need:
- 3 relay coils (I had some with 200 and others with 600 windings);
- 1 HD magnet;
- 3 diodes (general purpose diodes are ok, I used 1n5818 schottky for the low voltage drop);
- 18 blue LEDs (you may use how many you want or even other colors - white is also cool).
For the continuous mode just add:
- 1 capacitor (4700uF seemed fine, you could test some other values);
- 1 switch to be able to choose between modes.
Each coil is placed in series with a diode and three of these configurations in parallel. This way when one coil is providing energy, that power will not be consumed by the two other coils (simple half wave rectifier). The current flows directly to the LEDs where the voltage is the one generated by the coil with about 0.6V drop at the diode in case of a general purpose one. For a schottky it should drop only 0.3V or even less.
When the capacitor is connected to the circuit, it will be charged and will keep the LEDs on for some time when no coil is providing power.