An old solar powered street number sign was in front of our house when we moved in ten years ago. It has never worked and the solar panel has been missing. I used parts from this sign to create a new one that could function in the cloudy, wet, short winter days of the Pacific Northwest.
Step 1: Some New Parts
I decide to replace the entire power system with new components sized to achieve my performance objectives. As usual, adafruit.com had some great components to make this project easy. First is a lithium ion battery charger (part number 390) designed to be used with a solar panel as the charging source. You can read all the details on the website, but it basically utilizes a lithium ion charging circuit with a capacitor that stores up enough energy to pulse charge the battery. Next, I selected a 2W panel (part number 200) which should typically provide enough energy to charge the system during the short winter months. The battery I selected (part number 354) is a bit more than required, but will serve to store enough energy to get though days where the solar panel is covered in snow. Finally, a simple photo cell (part number 161) will turn on the LEDs (part number 754) after dark.
Step 2: Control Circuit
I created a simple transistor controlled circuit to turn on/off the LEDs based on the light detected by the photo cell. I had tried to use the solar panel itself as the source for light/dark detection, but the charing circuit caused huge voltage ripples as the draw would come and go. I settled on an independent light detection source in order to keep things simple. As designed, each LED draws about 5mA at 3.7V, the transistor can support about 10 LEDs if needed.
Step 3: Putting It Together
I used some old cedar lumber from a fence to make a new box and reused the original diffuser and street numbers (after some significant cleaning). I placed the electronics into a water tight project box and just used some non-conductive adhesives and calk to put everything into place. I was not sure how the LED would need to mount in order to have the display light well, so I just left them all with several inches of wire enabling me to move them around.
Step 4: Final Product
After placing everything in the box and connecting it up, it was time to try it out.