Photo Sensitive Running Top

If you run at night this is for you. This lights up as it gets darker outside on two independent photocells and no micro controller!

Materials 

• 10 x 3mm red LEDs 
• 12 x 3mm white LEDs 
• 2 x PNP 2N3960 -E13 Transistors 
• 2 x 5mm Photocells 
• 1 x 22k Ω resistor (not pictured) 
• 2 x 47k Ω resistor
• Battery holder with a switch that holds two 3V batteries
• 2 x 3.3V batteries 
• Ribbon wire
• ~ 1 yard athletic fabric - anything stretchy and breathable 
• 1 yard 1 inch elastic  ( I used fold over elastic; its softer. Found at a craft store) 
• Piece of balsa wood (if you're using a laster cutter) 

Tools

• Soldering iron (and solder)
• Hot glue gun (and hot glue)
• Sewing machine (and thread)
• A brain (and food)
• Optional, but nice: Laser cutter

​Skills 

• Intermediate sewing/pattern making
• Beginner soldering 
• Laser cutting  
• Patience

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1. Solder and place the LEDs

Laser cut the pattern of your choice into a piece of balsa wood and your fabric. Then place the LEDs in the wood, and solder them together with ribbon wire (black (-), red and purple (+)), making sure your connections are good and your LEDs light up. You can trim the tails to about 2 inches.  Then pop into the fabric and hot glue to secure. Do this for all your red LEDs, and repeat for the white LEDs. 

2. Solder and place the transistor and photo cell 

Solder together the transistor and the photo cell. With the flat side up, solder one leg of the photocell to the left leg of the transistor, and the other to the middle. Solder the resistor to the middle leg after the photocell.The solder the positive line from the LEDs to the far right leg of the transistor (the one that doesn't have anything else soldered to it yet). Then use black ribbon wire to extend the leg that has the resistor, and red to extend the last, (far left) leg. Then cover with hot glue.

​** In the photo, each transistor only has 1 47k Ω resistor. When I put it together the first time, the white took all the energy when both strings of LEDs are on, so I had to put a 22k Ω resistor in. 

3. Sew it all together and add the batteries

(1) Cover the line of LEDs with a strip of fabric, secure with hot glue. ​(​2)  Shape the top hem by folding over the top edges, feeding the wire in the seam towards the right, and sew into place. (3) Chalk out then sew the side seams. (4) Measure and attach the elastic straps. (5) Solder the positive line of the back to the positive line of the front. Extend ribbon wire from that solder joint 14 in, and solder to the positive line of the battery pack. Cover all exposed solder joints with hot glue. Repeat for the negative line. 

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4. More sewing

Sew wire in seam: Sew another line next to the seam created when you sewed the front and back together, and feed the thread through. Sew together the straps: This simply makes it so they don't slip around. Hem it: Pin wherever you want the hem, and sew it with a zig zag stitch. Create battery pocket: Sew a bit of fabric on three sides on the inside of the top, that will fit the battery and whatever excess wire is about. I made it so the tube the wire was in extended around the bottom of the pocket so you don't see the wire. 

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Done!