I am looking around for a nice easy to use setup for running student mbed projects off of solar power. I have seen a couple modules with a small solar panel and battery. I suspect there are probably some other options out there. I also need to tell students how to reduce power consumption (just a bit) at times and I have seen a couple forum posts about it, so I realize that you will not get to really low power levels. I need several, so I would like to avoid building things up, if possible.

So here are a couple of the small solar power modules with a charger and internal batteries in the $50 range that I found:

One for Arduino and other microcontrollers from http://www.nuelectronics.com, but they say out of stock. Are there other sources for it?

And this one from Wagan Tech to charge cell phone and USB devices with an internal battery is available from http://www.frys.com.

Has anyone seen some others I should look into - perhaps with a bit more power?

This could lead to quite an interesting competition - alternate ways of powering mbed!

You could make the students turn a handle and power it off a dynamo, or steam power, or small wind turbine, etc etc...

Hi !

Very interesting.

I work on something like you.

I try an boost DC/DC circuit to give power to my mBed with a single AA NiMh battery with success.

The boost DC/DC converter is the LTC3525 3.3, only 1 self and 2 capacitors -> fantastic.
Alternative : TI TPS61097-3.3

Now i will try to add a little solar charging circuitry to perform a solar floating charge of the AA NiMh battery... solar cell come from "low cost garden lamp" (just for example : http://www.supplierlist.com/photo_images/51214/Solar_Garden_Light-Stainless_Steel_Lamp.jpg).

Chris.

My guess is that you probably need several of those from the solar garden light to get enough power out of it. Just by looking at the surface area in the other Solar panels that put out around 1-3 watts.

Might even look at one of the larger solar garden light setups like this one http://www.homedepot.com/Lighting-Fans-Landscape-Deck-Lighting/Hampton-Bay/h_d1/N-5yc1vZarq9Zp4Z1xg1/R-100649216/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

But then it is getting near the $50 price range and probably not as neat of a package as some of the others. This one has 3 Ni-MH AAs in it and I suppose it might be nicer for a permanent setup outside.

Here you can find some solar chargers, with battery or individual solar cells. I use to by from Dealextreme for some time.

http://www.dealextreme.com/search.dx/search.solar%20panel

That site sure has a nice variety of them. The one you show looks like a really good deal. http://www.dealextreme.com/details.dx/sku.42139  . The area for the Solar cells looks a bit small for the power mbed would use while running, but they do not say anything about Solar power output. My guess would be about .5W based on the others.

This one seems to be about the next step up in power. It is about the size of a laptop, but it runs $200. http://www.thinkgeek.com/gadgets/travelpower/e193/

So it looks like you really need to decide if the mbed will run at night from batteries, and if you really want it to be able to charge batteries while the mbed is running.

As someone suggested a few posts back, one of the crank LED flashlights or radios could also be hacked to generate power. This one is $5 from http://www.ccrane.com/lights/led-flashlights/mini-dynamo-wind-up-led-flashlight.aspx. Looking at the power output info it looks like it might run mbed as long as you keep cranking it fast!

And there are even some small wind turbines available with 5-10W or less of power in the $200 or less price range. This one above is from http://www.fswindpower.com/Mini10W.html

And yes, someone has already even combined all three in one unit (solar, crank, wind) in this $75 one from http://store.sundancesolar.com/hywisohychfo.html

Sundance Solar  also has some basic DIY solar charger kits.

along with some of the rollable Solar cell setups.

I got one of those cell phone charger hand crank gizmos at a conference in Seoul a couple years ago. So I dug it out at home and it just happened to have the correct USB connector in the kit to power an mbed. So here is perhaps the first hand crank powered mbed blink LEDs project!

It's not easy being green, you have to turn the hand crank pretty fast. Note that when I slow down a bit at the end the mbed crashes.

It looks like a number of places still sell them for around $12. Here is one I found with a search at http://www.atomicmall.com/view.php?id=159481 

Solar, Battery, Car, and AC power for mbed in one small module.

I got one of the Wagan Solar e Power II model 2558 solar cell charger modules in from Fry's and gave it a try. Overall the quality seems OK. Just a bit larger than an older cell phone or a billfold.

The mini USB cable provided with it fits mbed, or you can plug the larger mbed USB cable into it's two USB connectors on the side. Either way it just plugs in without mods. Flip the power switch and my mbed is running. The case opens up to expose two Solar cells - a bit more area than some of the lower cost ones. A small red LED lights up when the Solar cells are charging the battery.

Here it is above running the blink LED example code  and you can see the relative size. So the specs say that the Solar cell output is 5.5V at 1.65W and it will generate 300MA of charge current from the Solar cell. Internal lithium batteries are 2000 mAH and the output with both USB  connectors can be up to 1A. The output can be switched in three ranges from 4.5-9V. It comes with a car lighter plug and an AC adapter (90-240V) for charging without Solar. It also has an LED flashlight feature and adapters to charge most cell phones.

Overall not a bad way to go for a mobile mbed setup - as long as it does not need a lot of current for external devices. The students bought a really cheap Solar charger (a real no name brand) first and it turned out the Solar cells were not even connected on it! It was just a battery pack with an AC charger. Perhaps this one is a bit pricey, but everything seems to work, it's handy, and no mods are needed out of the box.

CPC are offering a solar charger with integral batteries. Rated at 5.5V 500mA

Their part number BTO459301

web is www.cpc.co.uk

On the CPC one, is that 500MA from a charged battery or directly from the Solar cell? The specs seem kind of iffy and hard to find on all of them. I have seen several reviews for some of the different ones where people say they can never seem to charge the batteries from the Solar cells even in an entire day. Given the one we took apart and found that the Solar cells were not even connected, I can believe it. Quite a few of them only generate about 150MA of output directly from the Solar cells, when you can find the specs. I guess the other issue is likely to be what happens on a typical cloudy winter day - probably will need several of them for enough output.

That must be the current from a charged battery.

http://mbed.org/users/simon/notebook/interface-powerdown/ has new firmware that turns off the "magic" USB interface chip allowing the mbed to use the low power sleep modes. If you are running off limited power (i.e., Solar, Wind, Battery), you will want to check it out.

 http://mbed.org/users/no2chem/notebook/mbed-power-controlconsumption/ has some info on power and some functions to save power.

So using the two ideas above here is a code example that cuts power consumption by a bit more than half on the mbed.

#include "mbed.h"
#include "PowerControl/PowerControl.h"
#include "PowerControl/EthernetPowerControl.h"
// Need PowerControl *.h files from this URL
// http://mbed.org/users/no2chem/notebook/mbed-power-controlconsumption/

#define USR_POWERDOWN    (0x104)
int semihost_powerdown() {
    uint32_t arg;
    return __semihost(USR_POWERDOWN, &arg);
}

DigitalOut myled1(LED1);
DigitalOut myled2(LED2);
DigitalOut myled3(LED3);
DigitalOut myled4(LED4);

Ticker blinker;
int count=1;
void blink() {
    count = count << 1;
    if (count > 0x08) count = 0x01;
    myled1 = count & 0x01;
    myled2 = count & 0x02;
    myled3 = count & 0x04;
    myled4 = count & 0x08;
}
int main() {
    int result;
// Normal power level around 690mW
//
// If you don't need networking...
// Power down Ethernet interface - saves around 175mW
// Also need to unplug network cable - just a cable sucks power
    PHY_PowerDown();
// If you don't need the PC host USB interface....
// Power down magic USB interface chip - saves around 150mW
// Needs new firmware (URL below) and USB cable not connected
// http://mbed.org/users/simon/notebook/interface-powerdown/
    result = semihost_powerdown();
// Power comsumption is now around half
//
// use Ticker interrupt and Sleep instead of wait - saves around 70mW
// Sleep waits for an interrupt instead of executing instructions
    blinker.attach(&blink, 0.0625);
    while (1) {
        Sleep();
    }
}

jim hamblen wrote:

Units of power, in the below, are said to be mW. Is is indeed mA?

The key to battery life is the ratio of CPU and peripherals on-time to off-time. The power consumption can be rather high, of course, if the ratio (duty cycle) is low, like 20% or less.

 

 

#include "mbed.h"
#include "PowerControl/PowerControl.h"
#include "PowerControl/EthernetPowerControl.h"
// Need PowerControl *.h files from this URL
// http://mbed.org/users/no2chem/notebook/mbed-power-controlconsumption/

#define USR_POWERDOWN    (0x104)
int semihost_powerdown() {
    uint32_t arg;
    return __semihost(USR_POWERDOWN, &arg);
}

DigitalOut myled1(LED1);
DigitalOut myled2(LED2);
DigitalOut myled3(LED3);
DigitalOut myled4(LED4);

Ticker blinker;
int count=1;
void blink() {
    count = count << 1;
    if (count > 0x08) count = 0x01;
    myled1 = count & 0x01;
    myled2 = count & 0x02;
    myled3 = count & 0x04;
    myled4 = count & 0x08;
}
int main() {
    int result;
// Normal power level around 690mW
//
// If you don't need networking...
// Power down Ethernet interface - saves around 175mW
// Also need to unplug network cable - just a cable sucks power
    PHY_PowerDown();
// If you don't need the PC host USB interface....
// Power down magic USB interface chip - saves around 150mW
// Needs new firmware (URL below) and USB cable not connected
// http://mbed.org/users/simon/notebook/interface-powerdown/
    result = semihost_powerdown();
// Power comsumption is now around half
//
// use Ticker interrupt and Sleep instead of wait - saves around 70mW
// Sleep waits for an interrupt instead of executing instructions
    blinker.attach(&blink, 0.0625);
    while (1) {
        Sleep();
    }
}

Divide by 5 for mA - assuming you are using 5V power on the mbed Vin pin

I am putting some more info on it all at http://mbed.org/cookbook/Power-Management with links to where the functions came from.

http://www.sparkfun.com/products/9241 is a solar cell from Sparkfun that looks like it might be about the right size (about 8V 500MA) - price is about the same as the mbed.

http://www.outdoorgearlab.com/Portable-Solar-Reviews has reviews of several new Solar panels and battery packs.

They like the ones from http://www.goalzero.com/

They had a demo booth last month at my local Costco warehouse. Looks like they have a wide range of nice quality stuff - not the lowest $ but perhaps worth it.

Solar power generation is very important for modern times, especially the popularity and use of modern solar lamp. http://http://www.sresky.com/product/product.php?class2=75