Firefly Cap - Great Scott Gadgets

Great Scott Gadgets

Firefly Cap

An electronics kit for building a jar of fireflies or powering your own device with indoor photovoltaic energy harvesting.

Firefly Cap photo

Unfortunately, the Firefly Cap Kickstarter campaign was unsuccessful, but you can still build your own.

Firefly Cap hardware design files and firmware source code are available on GitHub.

Assembly Instructions

To build a jar of fireflies, use the following instructions (currently in development). For technical information you’ll need if you want to do something else with the Firefly Cap, see the wiki on GitHub.

  1. Acquire the necessary materials and equipment. You’ll need a soldering iron and some solder. Your Firefly Cap should come with 12 LEDs. You can use your own LEDs if you want instead (but only if they have a forward voltage of 2.2 V or less). You’ll also need a standard Mason jar with a lid the size of the Firefly Cap (not the larger three inch size).

  2. Locate points P1, P2, P3, and P4 on the underside of the Firefly Cap. Each one is marked with a circle and a label.

  3. Check the polarity of your LEDs. Usually the anode (the side that connects to higher voltage) has a longer lead than the cathode (the low side). When I say “solder the LED from P1 to P2” I mean that the anode should be connected to P1 and the cathode to P2. It is important to get the orientation correct.

    (Actually, If you get the orientation wrong, it will still work, but only if you consistently get them all backwards.)

  4. Solder two LEDs to the Firefly Cap.

    • Connect one LED from P1 to P4.
    • Connect one LED from P2 to P3.

  5. Solder two LEDs to the leads of the LEDs soldered in the previous step.

    • Connect one LED from P1 to P2.
    • Connect one LED from P3 to P4.

  6. Solder two LEDs to the leads of the LEDs soldered in the previous step.

    • Connect one LED from P1 to P3.
    • Connect one LED from P2 to P4.

  7. Solder two LEDs to the leads of the LEDs soldered in the previous step.

    • Connect one LED from P4 to P1.
    • Connect one LED from P3 to P2.

  8. Solder two LEDs to the leads of the LEDs soldered in the previous step.

    • Connect one LED from P2 to P1.
    • Connect one LED from P4 to P3.

  9. Solder two LEDs to the leads of the LEDs soldered in the previous step.

    • Connect one LED from P3 to P1.
    • Connect one LED from P4 to P2.

  10. Connect the photovoltaic panel to the circuit by soldering a pin header to location P5. Install a jumper on the header.

  11. Install the Firefly Cap into the lid of a Mason jar, replacing the flat lid but using the ring to hold the Firefly Cap in place.

  12. Your jar of fireflies is complete! To test it, place it in moderate to bright light for an entire day and then watch the light show when it gets dark.