Tuesday, November 27, 2012

A home-made Voltaic Pile

Back from my trip to Italy and visit to Tempio Voltiano I decided that I really ought to make my own Voltaic Pile. So, I gathered together the following easy to obtain items: British 2p coins, zinc coated disks of metal, some blotting paper and a bottle of vinegar.

The British 2p coins are copper (at least on the outside) and so, with the zinc disks, will make the two electrodes of each cell in the pile. The vinegar is the electrolyte and the blotting paper is used to separate the metals. I got the zinc disks by buying the cheapest electrical junction box I could find and punching out all the holes:

Each cell consists of a 2p coin, a piece of blotting paper soaked in vinegar and a zinc disk:

Each cell gave roughly 1.02v (apparently zinc-copper should be 1.1v at 25C) and then it's just a question of making a pile of them to make a larger voltage. This pile of 10 cells had a measured voltage of 9.7v (clearly not all the cells are at 1.02v).

And there's sufficient current to light an LED:

To make it easier to connect to the bottom of the pile I sat the whole thing on a small piece of aluminium foil.

The greatest Google Mail feature you may not be using

There's a wonderfully powerful and subtle technique in Google Mail that can be used to enhance every reply you make to a mail: if you select an area of a message and then hit Reply only the selected text will be quoted in the response.

For example, here's an email I need to reply to:

If I simply hit Reply then the entire original message is quoted in the response:

But if I first select the piece that's important to me:

And then hit reply, only that part is in the response:

Use this to respond to just the right parts of a message and cut down those enormous chains of replies where the messages grow and grow and grow.

PS This feature has been disabled by default in Google Mail. You must enable it to use it.

Sunday, November 18, 2012

The Bergamo Analemma

While in Italy I briefly visited Bergamo and stumbled upon a wonderful projection of the Sun's analemma in the old town. A hole in a metal disk causes a dot of sunlight to be projected on the ground and the path of the Sun throughout the year is recorded by keeping track of the position of the Sun at local noon. The path of the Sun is an analemma. In Bergamo the position of the dot has been permanently engraved in the stone work:

In the photograph you can see the curved line that shows the local noon position of the Sun as projected through a metal disk. At the top of the image you can just make out the metal disk that has the hole used to create the track of the Sun on the ground. The two ends of the analemma represent the summer and winter solstices. The central line is a meridian and the photograph above is facing south. Here's the compass rose at the end of the meridian line:

Here's the disk:

And the position of the solstices:

All along the meridian line are the days of the year laid out so that the date can be determined from the angle of the Sun at solar noon.

I didn't manage to get a good shot of the characteristic elongated figure-8 shape of the analemma itself. The ends of the 8 are the solstices. The two outer lines parallel to the meridian show 15 minutes before and after solar noon.

Thursday, November 08, 2012

"That'll Never Work!"

I got invited to speak at the last Hacker News London meet up and gave a talk called That'll Never Work! about crazy ideas and what to do about them. The organizers have now posted the talk video:

If you want the slides themselves then here they are:

Wednesday, November 07, 2012

The Rizzoli Conundrum

I was in the Rizzoli book shop in Milan buying The Economist when I noticed that the wear pattern on the pinpad used to pay using a debit card was anything but uniform.  Unfortunately, I didn't have my phone with me so was unable to snap a picture, but it looked like this:

There was heavy wear on the buttons 1, 4, 7, 8, 9 and the green OK button. The buttons 2, 3, 5 and 6 showed little wear. What could cause this?

At first I assumed that Italian debit cards had four digit PINs and people might be able to choose their PIN and use a birth year. To check that I grabbed the latest statistics on the number of people living in Italy by age (statistics are available from ISTAT in CSV format) and wrote a small program to process that. Based on people aged 18 to 80, assuming 4 digit PINs equal to birth year the wear pattern would be: 9 (29.08%), 1 (27.46%), 7 (7.39%), 6 (7.34%), 5 (6.39%), 8 (6.19%), 4 (6.13%), 3 (4.84%), 2 (2.70%), 0 (2.47%) (which isn't terribly surprising as there would have had to be a sudden drop in the birth rate in 1950s and 1960s Italy for the observed pattern).

Then I asked some Italians about their debit card PINs. Italian PINs are 5 digits long (not 4) and are chosen by the bank and cannot be changed.

So, can anyone come up with an explanation of what I observed?

PS If anyone's in Milan and can walk into Rizzoli and snap a picture of the pinpad (at the till straight in the front door) it would be cool.

Monday, November 05, 2012

Tempio Voltiano

At the bottom tip of Lake Como one of the most (if not the) most over-the-top memorials to a scientist is found sitting on the edge of the lake. The Tempio Voltiano is a temple built to commemorate the Italian scientist Alessandro Volta (who, amongst other things, invented the battery). Built in 1927 the temple depicts Volta as a classical figure. In central Como there's a statue of Volta (on the Piazza Alessandro Volta) with the scientist draped in robes as if he were a figure from the Roman era.

The temple itself continues the theme, with statues representing science (on the left of the entrance) and the Roman goddess Fides (Goddess of trust).

And the interior is similarly grand with an inlaid floor of marble, alabaster and other stones. The circular  layout follows the progression of science that Volta worked from the left to right with the dates engraved in the stonework.

The actual exhibition is a little disappointing. In 1899 Como put on an enormous exhibition celebrating the 100 year anniversary of the Volta's invention of the battery. A massive fire broke out and many of Volta's original instruments and creations (including his batteries) were destroyed. The temple contains those artifacts that remain augmented by reconstructions based on parts that were recovered.

Nevertheless it's here that you can see some of the first batteries ever created. Such as this Voltaic Pile:

And there's a good display of other batteries made by Volta using a variety of metals and electrolytes (some of them dry and some of the wet technologies):

And here's some equipment used for electrolysis to see what gases are generated at the anode and cathode.

Volta's invention came about because of Galvani's investigation of 'animal electricity' that appeared to be exhibited when frogs' legs moved when placed in contact with two different metals. Volta didn't believe Galvani's explanation of the presence of electricity in animals, but rather thought the the contact of the metals and the legs was creating electricity. In disproving Galvani he invented the battery.

Also, on display is equipment that Volta used to measure the electromotive force by balancing weights against two charged plates to measure the force required to separate them. And there's a display of capacitors (which he called 'condensors' because the electricity was thought to 'condense' on the plates).

If you visit the museum be sure to ask for the handout in English that describes all of the numbered exhibits and buy the 6 Euro English-language "Guide to the Volta Temple" which is well worth reading as it covers the history of the building and Volta's inventions in detail.

Making an old USB printer support Apple AirPrint using a Raspberry Pi

There are longer tutorials on how to connect a USB printer to a Raspberry Pi and make it accessible via AirPrint but here's the minimal ...