Hydrogen powered Pi?

There is no "by design" here - you probably misunderstood sudo and the shell - the redirection is run as your normal user...

Try this:

sudo /bin/bash -c "echo 0 > /sys/devices/platform/bcm2708_usb/buspower"

but maybe put it in a bash script with a sleep 10 then echo 1 to re-enable if it doing it via ssh or even local keyboard.

Or just pull the plug to reboot it...

Gordon

Reply to
Gordon Henderson
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That's not a particularly nice way of saying it. I forgot. Alternative I used before is 'tee':

echo 0 | sudo tee /sys/devices/platform/bcm2708_usb/buspower

Reply to
A. Dumas

And, as its a high temperature process, its energy efficiency will be low, if only because bulk industrial processes running at high temperatures tend to have fairly poor insulation wrapped round them and, anyway its an strongly endothermic process, much as you'd expect. Efficiency is said to be 65-75%, i.e. up to 1/3 of the energy put into the conversion is lost.

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martin@   | Martin Gregorie 
gregorie. | Essex, UK 
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Reply to
Martin Gregorie

Raspian has SSH available to the serial port at any time. I'm not sure if others have it enabled, but it would be good to know how to because it is a simpler than using the network as well as a viable alternative for headless access. That is, assuming you have a serial port and terminal program on your second computer. (and the appropriate level shifter 9 pin adapter for the Pi) Ron M.

Reply to
Ron

Another way to direct stdout from a process with the redirection done as root is to use 'dd':

echo something | sudo dd of=/some/path

runs 'dd' as root, opens /some/path as root, and channels the data output by the left-hand process into the file. Options for block size can be added for efficiency if handling a lot of data.

HTH

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Robert Riches 
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Reply to
Robert Riches

if you can store the hydrogen in an effectively negative-weight balloon instead of a heavy tank it may be more suitable for the high-altitude guys :)

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For a good time: install ntp
Reply to
Jasen Betts

Good one. Under Raspbian, /etc/inittab controls whether a login terminal is available at the serial port. At the bottom of that file there should be:

#Spawn a getty on Raspberry Pi serial line T0:23:respawn:/sbin/getty -L ttyAMA0 115200 vt100

On the other hand, if you need the serial port for something else and don't want interference from the OS, you should comment out that line, edit /boot/cmdline.txt to remove ttyAMA0 references, and reboot. Specifics can be found on the web.

"USB serial / debug / console cable" available from shops like

formatting link
and
formatting link
(same cable; 5 V power, 3.3 V logic).

Reply to
A. Dumas

Thanks, that cable makes things easy, I overlooked it mainly because RISC OS doesn't have an established USB-serial driver yet. I think the last time it was tackled the PL2303 chip was friendlier than the others so something might eventuate. If the second computer was a RasPi also, pin to pin connections would be OK I think. I have heard of a GPS module connecting to serial this way OK as it is a 3.3V logic also.

Ron M.

Reply to
Ron

... From a ruddy great tank of the stuff in Emeryville... (:-P)

Actually, I did a bit of digging, and they do have an electrolyser on site that can provide enough (60kg) for two bus loads/day, but most does indeed come from methane reforming.

The object of the exercise with buses is of course to reduce pollution, but I guess it must be economic or they couldn't do it.

They do claim an overall reduction in CO2, even from the methane chain. (The headline says "nearly half" vs. diesel...)

-- Pete --

Reply to
Pete

That's because methane has four hydrogen atoms per carbon, while long chain saturated hydrocarbons asymptotically approach two hydrogens per carbon.

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-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon
Reply to
Michael J. Mahon

Indeed. Actually, you need to put in *more* energy than you'll get back from the oxidising the hydrogen because electrolysis is not 100% efficient. A tankfull of hydrogen is best regarded as a form of energy storage, i.e. the equivalent of a rechargeable battery, rather than as a source of energy.

Hydrogen is difficult to store because, as a compressed gas, the stored energy per litre is quite low. The tank tends to be big due to the low energy density of compressed hydrogen and heavy because of the high pressure it has to contain. The result is that the energy you get back, regardless of whether you use a fuel cell or a conventional IC engine is very low in terms of the size and weight of the tank by comparison with a tank of petrol.

Cryogenic storage has other problems: while its a big improvement in both volume and weight over compressed hydrogen, it has the huge problem that about the only way of keeping the stuff liquid is to allow it to boil off. IOW, this really only works if you're going to use the entire tankfull as soon as its been filled. This works for rockets and for buses provided that they get through a tankful in a day or less and are never allowed to sit overnight with anything in the tank. Last but not least, you really don't want to leave a vehicle with a tank of LH in a closed garage: the fire hazard from doing that is rather high.

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martin@   | Martin Gregorie 
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Martin Gregorie

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