Wednesday, January 30, 2013

Ice Waves

On a walk in my home town, I came across something which I at first couldn't understand at all - it was water slowly running down an icy rock face, which had created a weird mushroom-like structure.

Friday, January 25, 2013

Wintry Moiré

I saw an awesome Moiré pattern, formed from two perforated sheets of metal at slightly different distances from the camera. This gives a slight size difference, and therefore a slight frequency mismatch for the two sheets. It's nice how the original hexagonal pattern of the holes is repeated, hugely, in the Moiré pattern (much nicer than the boring examples on Wikipedia)!

Monday, January 14, 2013

New Hama Anti-Ad Sign

Our previous 'no advertisements' sign proved so popular that it was actually stolen (or anyway, it disappeared, most likely it fell down and was cleaned away or something). So I made a new one.

The new sign is made with Hama beads, like the old one. The sign has 01 White text on a 17 Grey background. I also made a glow-in-the-dark frame, with 55 Glow-in-the-dark green and 57 Glow-in-the-dark blue. It looks quite nice, a pop of bright color in the dark hallway, but it was very difficult to photograph!

The text, "Ei mainoksia kiitos!", is Finnish for "No advertisements please".

Sunday, January 6, 2013

Nut Domains

The square nuts from our Meccano set. Pushed together randomly, they form nice orientation domains - little areas where each square lines up with its neighbors.  Gaps open up between these domains, since they are not  lined up with each other.

The pattern reminds me of a city map, where rectangular buildings on a block are lined up, and then at a bigger street, the angle changes.

Wednesday, January 2, 2013

Wiring A Wireless Doorbell

Wireless doorbell

My father-in-law installed a wireless doorbell. The ring-button outside the door contains a battery and a radio transmitter, the indoor unit contains a radio receiver and a speaker. It turned out that the battery in the ring-button outside does not like the cold Finnish winter, so it went flat. It seems this doorbell is best suited for indoors use...

We planned to replace the transmitter with an old-fashioned switch with wires, and move the transmitter indoors. Opening up both the receiver and the transmitter first revealed a rather sloppy soldering job, then something about the design of the transmitter and receiver.

Wireless doorbell LP8029

The transmitter contains an encoder chip LP801B, while the receiver contains a LP8029 decoder. The radio circuitry appears to be built with discrete components in both units. The transmitter circuit board has two push-buttons: one for ringing and one for changing the melody. Only the ring-button is accessible when the cover is closed.

The receiver contains a melody generator chip, under a black plastic blob. Both units have a bank of four dip switches. Pressing the transmitter button causes a noise inside only if the switches in the receiver and transmitter are in identical positions, this is to avoid hearing the doorbells of all neighbors.

modified wireless doorbell

The initial plan was to move the transmitter inside, and connect the ring-button outside in parallel with the ring button on the transmitter. After a look at the Japanese LP8029 data sheet, I found a point in the receiver circuit that starts the ringing noise when momentarily connected to the positive supply. I wired the outdoors button to this point. The transmitter module is now needed only for selecting the melody, the receiver on its own works as an old-fashioned wired doorbell.


It was hard to find any information in English about the LP801B and LP8029 chips. An Austrian hacker found the same encoder chip in the transmitter for radio controlled mains switches. He figured out how to connected the transmitter to a microcontroller, to switch things on and off from a program.
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