Jar of Fireflies

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About the Jar of Fireflies project

Mason jars outfitted with LEDs and a small microcontroller programmed to mimic the behavior of fireflies caught on a warm summer night. The addition of a piezo sensor enables a degree of interactivity that everyone wished their jars did as kids; tap the jar, and the lights react! Based on an old project found on Instructables, this project includes a number of great updates, including Arduino compatibility, interactivity and easier-to-use parts! Plus, the entire project embraces the principles of Open Source Hardware (OSHW), which means you can learn from and modify all of the code, design files, schematics and more for free!

Project links

And watch for activity on this project's official Github repo:


Project goals

  • Use the ATTiny85 microcontroller with HLT's Arduino bootloader to make programming easy.
  • Use through-hole components to make assembly easier, with the option to use SMD LEDs.
  • Add interactivity using a piezo sensor.
  • Include a variety of interchangable power options
  • Include a wealth of high-quality documentation, to make assembly and troubleshooting easy
  • Minimize parts count and build complexity to make this kit suitable for teaching soldering
  • Adhere to OSHW 1.0 definition, keeping all code and design files open


  • ATTiny85 microcontroller mounted with a DIP IC socket, so it can be easily removed and reprogrammed externally using HLT's Arduino bootloader (see http://hlt.media.mit.edu/?p=1695).
  • Six charlieplexed LEDs (with the option to use SMD LEDs with fancy soldering).
  • Piezo sensor to detect tapping for interaction.
  • Four ways to connect power to the board - standard 2.1mm DC jack for wall adapters, 2-pin JST for batteries, 2-pin screw terminal for raw wires and 2-pin male header for female jumper wires.
  • Contacts for alligator clips so multiple jars can be daisychained to a single power source.

Bill of materials

Source files

All of the latest source files, including Eagle files, BOMs and firmware, can be found at this project's official Github repo:


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