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At Maker Faire Austin, Evil Mad Scientist Labs was demonstrating some really simple and useful circuits powered by solar cells. Today, they’ve posted the details on their site.

Interruption-resistant direct drive:
The “direct drive” circuits work well for their design function, but are rather basic. They provide no energy storage, and so are quite vulnerable to blinking out when a bird or cloud passes overhead. For some applications, like running a small fan or pump, that may be perfectly acceptable. For other cases, like powering a microcontroller or other computer, a brief power interruption can be disruptive. Our next circuit design adds a supercapacitor as a “flywheel” to provide continued power during brief interruptions.

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Adding a microcontroller:
Our last circuit examples extend the previous designs by adding a small AVR microcontroller. We use the voltage output from the solar panel again to perform darkness detection, but instead take it to an analog input of the microcontroller. The microcontroller is potentially a very low current, efficient device that lets you save power by not running the LED all the time, but (for example) waiting until an hour or two after darkness and/or fading the LEDs on or off, or even intermittently blinking for very low average power consumption.

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Simple Solar Circuits

Gareth Branwyn

Gareth Branwyn is a freelancer writer and the former Editorial Director of Maker Media. He is the author or editor of a dozen books on technology, DIY, and geek culture, including the first book about the web (Mosaic Quick Tour) and the Absolute Beginner’s Guide to Building Robots. He is currently working on a best-of collection of his writing, called Borg Like Me.


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Comments

  1. Gadre says:

    The upper end of the inductor needs to be connected to the positive terminal of the battery and not to the PWM output.

  2. Windell Oskay says:

    The schematic as drawn works well. Ours may not be the most conventional design, but it is functional indeed.

    Changing it (as suggested) to connect the inductor to the battery instead of the PWM output would *not* work. It would remove the darkness detection capability of the circuit. The reason is that when the solar cell output is high, that voltage after the diode is high enough to directly drive the LED, even without a voltage boost. This also means that less current is available to charge the battery in sunlight. It could also potentially destroy the LED by allowing too much current to pass through it.

  3. jammit says:

    @Gadre
    I understand where you’re coming from. When I first saw the schematic I thought the same thing. I realized they weren’t really trying to make plain “joule thief”, but a combo voltage booster and flasher. When the transistor first turns on it saturates (or almost) the coil. After the transistor turns off, the coil dumps its load into the LED. In this way there’s no leakage current into the LED when it’s supposed to be off. The only mod I would do is to put the LED across the inductor, with the anode connected to the collector side, and the cathode connected to the PWM output. The way the coil dumps into the LED now is through the parasitic diode in the PWM pin. Since the LED is a diode anyway, you don’t need that, plus the LED will clamp the reverse voltage spike to its forward drop.

  4. from where i can get these small solar panels…..
    and also tell me the cost in details as soon as possible

  5. from where i can get these small solar panels…..
    and also tell me the cost in details as soon as possible

  6. from where i can get these small solar panels…..
    and also tell me the cost in details as soon as possible

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