By Dionna Moore
Want to leverage your pumpkin’s untapped potential? Root3 Labs has created an easy guide to help you build your own self-powered illuminated pumpkin.
Need: A pumpkin that can illuminate itself without a candle or an external power source.
Objective: Utilize the acidity of a pumpkin’s flesh to make a galvanic battery and use this electrical energy to power multiple LEDs that will illuminate the pumpkin.
Design: The pumpkin circuit is shown in Figure 1. Each battery represents a section of pumpkin physically isolated from the rest of the pumpkin. The sections are connected in series to produce a resulting voltage of roughly 5V. This value will vary depending on the selected pumpkin.
Figure 1– Schematic showing the pumpkin circuit.
Materials: (See Figure 2.)
Figure 2 – Materials used throughout the experiment.
- (Qty 1) Pumpkin (5+ pounds)
- (Qty 2) LED’s (any color)
- 28 AWG insulated wire (7 ft of green, 7 ft of red)*
- Solderless Breadboard*
- (Qty 6) 1”x1” piece of copper
- (Qty 6) 1”x1” piece of pure zinc
- Plastic Wrap or Ziplock Bags
- Electrical tape (optional)
* If soldering is unavailable to you, use alligator clips with test leads instead of a solderless breadboard and 28 AWG wire. *
Step 1: Cut, Clean and Prep Pumpkin
Pumpkins are my least favorite thing to clean out, but make sure you clean out all the seeds and guts so you can cut out sections in the pumpkin without making a mess. If you would like to carve a special design in the front of the pumpkin, I recommended that you cut out the chunks of the pumpkin before cutting your design. Each section should be about 2”x 2”. Number them and take a picture for reference. Then, remove the cells. I carved out 6 cells for my battery to get the desired voltage of 4.7 volts (See Figure 3). An LED requires a voltage between 1.2 to 3.3V. Cells in series create an additive voltage. If one cell measures 0.7V, you will need between 2 and 5 cells (1.2V/0.8V = 1.7 and 3.3V/0.8V = 4.7). A higher voltage will result in a brighter LED.
Figure 3 – Sections of pumpkin cut out and labeled.
Step 2: Prep your Materials
- Create your 6 zinc and 6 copper 1” squares. I cut these plates from two larger sheets using cutting sheers and a Dremel.
- Prep your wire. Cut 6 pieces of red -28 AWG wire and 6 pieces of green -28 AWG wire all measuring 10-12”. Strip both ends of all the wires.
- Solder wire leads to your plates. Solder one end of the red wire to each copper piece and solder one end of the green wire to each zinc plate (See Figure 4). Use flux and create a solder pool on each plate before attempting to join the wire. The plates will require significantly more heat than the wire before the solder will begin to flow. The final product should be (12) pieces all together – 6 pieces of copper with red wire and 6 pieces of zinc with green wire.
- Prep your plastic wrap to isolate each pumpkin cell. Cut and separate 6 rectangular pieces of plastic wrap measuring 5”x 5”(this may vary based on the size of your pumpkin cells). Alternatively, you can use 6 plastic Ziplock bags.
Figure 4 –(Left) The zinc plate soldered to the 28 AWG green wire. (Right) The copper plate soldered to the 28 AWG red wire.
Step 3:Assemble your Pumpkin Battery Cells
- Insert 1 zinc plate and 1 copper plate into your first chunk of pumpkin (see Figure 5). Do not let the zinc and copper plates touch. There should be about one inch of space between the pieces to allow the electrons to flow through the rind between the plates.
- Using a multimeter, measure the voltage produced from that cell. The voltage should be between 0.7V and 0.8V. If your voltage is lower than 0.7V, try pressing the zinc plate deeper into the rind and re-test. Repeat this process for all the cells.
Figure 5 – Measuring the voltage between zinc and copper plates inserted into the pumpkin.
- Isolate each cell from the rest of the pumpkin. Without isolating each link, you are effectively shorting the pumpkin battery. Wrap each cell individually with the plastic wrap or Ziplock bags. To keep the wires together, add electrical tape. Then insert the cells back into the pumpkin, with the zinc and copper plates on the inside and the wires coming out of the top. (See Figure 6 and Video 1.)
Figure 6 – Wrap plastic wrap around the pumpkin sections and insert them back into the pumpkin.
Video 1– Assembling battery cells back into the pumpkin.
Step 4: Assembling the Pumpkin Cells in Series
- Connect your cells in series using a solderless breadboard. To connect the LEDs, insert the positive side (the longer lead) into any row on the solderless breadboard and the ground (shorter lead) into the negative rail. Next, take the red wire of the first cell and place it in the same row as the LED. Take the green wire from the first cell and place it in a different row from the LED or red wire. Take the red wire from the second pumpkin cell and connect it in the row with the green wire from the previous cell. Repeat the process of combining the green wire of the previous cell with the red wire of the next cell.
A pattern should start to occur and at the end you should be left with one green wire. The last green wire should go into the ground rail of the solderless breadboard to connect it back to the LED. Once you place the green wire in the ground, your LED should light up. If your LED does not light up, check the voltage between cells to make sure they are correctly linked in series. (See Video 2 and Figure 7.)
Video 2– Assembling breadboard to power LED’s.
Figure 7 – (Left) Breadboard schematic of series circuit. (Right)Wires assembled in the breadboard powering the LED’s.
- Alternatively, you can assemble the battery without soldering, using alligator clips. Connect the cells in series by connecting the zinc component of the first cell to the copper component of the second cell. Test the voltage across the 2 pumpkin pieces to make sure they are connected in series correctly. If the voltage did not double, then they are not connected in series. Repeat the process by connecting the zinc component of the second cell to the copper component of the third cell. Once all cells are connected, take one alligator clip with a test lead, and connect it to the first piece of copper. Repeat the same step and connect another test lead to the piece of zinc on the last cell. Lastly, check to see if the voltage increased by using the multimeter. (See Figure 8.)
Figure 8 –Measuring the voltage across 2 sections connected in series using alligator clips.
Step 5: Add Additional Items (Optional)
If you want to add any additional items to your breadboard before placing it inside the pumpkin, this is the time to do it. I added a toggle switch to the circuit to turn the LED off and on. To, do this, I just added the switch in series between the battery cells. (See Video 3 and Figure 9.)
Video 3– Installing a toggle switch.
Figure 9 –(Left) Breadboard schematic showing the toggle switch connected in the series circuit. (Right)Breadboard assembly with toggle switch.
Step 6: Illuminate Pumpkin
Now that your LED is on, its time to show off your masterpiece and light up the pumpkin. Place your breadboard inside the pumpkin, turn off the lights, and watch your pumpkin glow!
Figure 10–Breadboard installed inside of the pumpkin.
Figure 11 –Final Product; Pumpkin illuminated by LED.