Solar Powered Espruino

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  • I was thinking it'd be good to have a tutorial on making Espruino solar-powered, so I went and ordered a solar powered keyring torch from eBay, as it should have basically everything that's needed.

    Only problem is it has a standard non-rechargeable lithium cell and the solar panel isn't actually connected! I don't suppose anyone knows of a decent source of solar panel + battery that is cheap and actually works? :)

  • Hello Gordon,

    Only problem is it has a standard non-rechargeable lithium cell and the solar panel isn't actually connected!


    I've got some solar cells from this german ebay store. With this one I have powered an Atmega and a LCD. But it works only outside. A Lamp or sun shining through a window doesn't provide enough power. The 5V / 100mA of the cell is only reached with direct solar irradiation.

    I think the modules are from china and should be available in the UK, too.

    Btw: My espruino has arrived today (January 29) in Germany

  • Probably not exactly what you were thinking of, but I bought a 10,000 mAh battery pack with solar panel the other day specifically for running an Espruino.­X3OQI

    Unfortunately, this particular one is stupidly designed with the blue power-level indicator LEDs lit at all times while it supplies power to USB, rather than momentarily when a "test" button is pushed. No idea how well it'll work, but I've got an Espruino running off it at the moment. It's not a particularly fair test considering how little sunlight it's getting right now.

  • Thanks! That looks like quite a nice one actually. My guess is that the LED might run it down though. If you don't mind opening it (you might do if you paid £20 for it :) ) then soldering wires onto the internal Li-Ion battery would be perfect. Espruino can run off the battery's 3.7v without needing the step-up converter.

    I've just ordered a really cheap (~£5) battery pack, so we'll see how that one works.

    In the mean time, I found that by removing the voltage regulator in Espruino it lowers the power consumption to around 20-30uA which means that even the small solar cell from the torch above is enough to run it, even today!

    edit: I'll document that in a bit I hope.

  • That's a good idea... I was planning to open it up to add a momentary button for the LEDs anyway.

    I'm guessing the relationship between solar cell output for typical light level over 24 hours at various times of year, vs. charger/battery efficiency, vs. power drain by the Espruino (plus other drains, such as wireless modules) would be a pig to figure out.

    Any rough guesses on whether the solar cell kept in daylight charging up the Li-Poly battery would be enough to power the Espruino with a typical(!) activity load in perpetuity?

  • On yours I'd be pretty sure the solar cell gave out enough power or it'd never be able to charge the LiPo in any sensible time...

    A normal Espruino board takes 110uA in deep sleep mode, and if it woke up every minute for quarter of a second and drew 35mA, that's about 250uA on average. That means that on your 10000mAh battery it should last over 4 years - so unless it takes that long to charge off a solar cell I'd say you're sorted :)

  • Good point :)

    Clearly not that much of a pig to figure out then!

  • Thinking about this, is there a way to control when the Bluetooth radio is on? Or is there any Bluetooth LE module available? This is one of the rare thing that my RFduino has better than Espruino at the moment! Those RFduino are very very low power; maximum current is 18mA while transmitting on BLE with ultra low power modes down to 4uA. Not the same speed, features and size but its integrated BLE radio really rocks.

  • Hi, have you seen this post on the BLE module?­566/#comment6652

    It looks like you can just solder it on. There's also another post on entering low-power mode with the HC-05 (­). I'm not sure anyone has tried it yet, but even that can get down to 3mA. There might even be a way to programatically turn it off, and then only turn it on when you need to transmit data.

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Solar Powered Espruino

Posted by Avatar for Gordon @Gordon