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Posted: Fri Apr 12, 2013 8:08 am
by Jim JKla
I am not sure if this belongs in off topic but I know it's a safe place to put it.

Like some of my other posts please treat this as a thought experiment

If you feel like you need to post that you think it's not needed please feel free to keep your comments to yourself. :D

I have been wondering about field use of the RPi and there's been loads of discussion about battery and solar powered supplyied and in car RPi operation.

Given the nature of the beast and its operation I have been considering the use of Freeplay equipment, and given I can run my RPi headless from my laptop over Wi-fi I have been considering camping uses and my thoughts driffted back to my Freeplay Radio. That brilliant flash that kicked Trevor Baylis into the perception of the British Populus.

I know the original had a simple 3v output and that these devices have moved on a long way from the original concept.

In the light of those thoughts of camping use I have been thinking about a wind up USB hub with a couple of 10BaseT ports on for good measure.

The device could also be used for charging mobile phones.

After some consideration I decided you would need a small battery or capacitence driven audio warning so that you would know when to rewind before the power dropped bellow a level to sustain your RPi. Internet access is not an option as I am considering this for locations where internet coverage is at best patchy and at worst non existent.

But I am looking to the child enjoying a holiday in the UK subject to vagaries of British weather isolated in a caravan with a Rpi a laptop and time to tinker. ;)

Re: Freeplay

Posted: Fri Apr 12, 2013 1:11 pm
by drgeoff
You seem to be thinking of a power source where the energy is stored in a spring rather than in a rechargeable battery. I don't know the specific details of the Freeplay radios but I do know that a simple AM/FM radio will run and produce moderate volume with as little as 25 milliamps. An RPi takes much more than that so either the running time will be much less or the spring will need to be much larger.

Also, it is all very well to have such a powered RPi, but if it needs a display device .....

Re: Freeplay

Posted: Fri Apr 12, 2013 2:07 pm
by Jim JKla
This is why I was considering using a laptop and putty to access the RPi but look at this. ... aptop.html

Re: Freeplay

Posted: Fri Apr 12, 2013 2:33 pm
by drgeoff
Jim JKla wrote:This is why I was considering using a laptop and putty to access the RPi but look at this. ... aptop.html
Many laptops would power an RPi (without peripherals) from one of their USB ports. Still leaves the issue of what to do when the laptop battery conks out. :)

The article you link to is dated 2005. That MIT One Laptop per Child has already been produced in a couple of versions but I'm not aware that a hand cranked one has been produced in volume.

Re: Freeplay

Posted: Fri Apr 12, 2013 3:21 pm
by bwoodbury
Freeplay power has indeed come a long way ... egory_id=4

Note the last question in the FAQ about 5v output ... e-12v-faqs

Re: Freeplay

Posted: Fri Apr 12, 2013 4:28 pm
by AndrewS
bwoodbury wrote:Note the last question in the FAQ about 5v output ... e-12v-faqs
Hmmm, very conflicting information though :?

How many amps is the output at 12v?
Approx. 160mA.

How many watts does the Freecharge 12v deliver?
The Freecharge 12V is designed to deliver about 12W.
(12W at 12V would be 1A i.e. 1000mA)

How many mAmperes can your Freecharge 12V" produce?
It produces approx. 600mA at 12V.

Can the Freecharge 12V be used to power a smartphone (5V - 1400 mAh)?
Yes it will work (Even though the FC cannot give 1400mA). We assume that the 5V 1400mA is the rating of the Car Adaptor that you have and it's a switch mode type. Weassume that you are using a switch mode car adaptor to go from 12v to 5V for your smartphone. If so (most likely) the 12v from FC is then converted with his adaptor to 5V. Since the voltage goes down the current goes up. So 1400mA will mean that he needs about 800mA from FC. So it should work (if the assumptions are correct).

So probably not the best choice for powering a RasPi? Probably a bit hard to type when you're using both hands to crank the generator :lol:
I'd guesstimate that even if you used the Freecharge to charge a battery, and then used the battery to power the Pi, you'd probably only get about 10 minutes "Pi time" from 5 minutes of cranking?

Re: Freeplay

Posted: Thu Apr 18, 2013 12:01 pm
by mikerr
The Pi is only low powered compared to a PC (Pi 1W vs PC 100W)
but not compared to a typical radio ( < 0.05W )

and that's before considering a display.

The Pi also has no "suspend" state to conserve power, it uses a constant 1W whether in heavy use or idle unlike smartphones (or laptops!)
I've found that annoying when leaving pi on batteries and is drains flat, doing nothigng but idling !

But onto possibilities:

Since it would need higher / more constant power than a hand crank can provide I think a foot operated crank would work
-then you have your hands free for computing, and can sit with a foot pedal occasionally powering it
-thinking more organ pedal/ sewing machine pedal than bike pedal.

Seems what I imagined has been made, but all links are from 2009, didn't finally make it to market ? ... aptop.html