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• Great documentation about piezo

  ftregan • 07/01/2014 at 03:00 • 0 comments

  I found this documentation about piezo speakers:

  http://www.murata.com/products/catalog/pdf/p15e.pdf

  The most interesting part for this project is the one where they exaplin how to calculate dimension of a resonnant chamber. If paper resonnant chamber gives good results, I will modify the polyphonic algorithm so it can select the piezo with closer resonnant frequency for each played note.

• Cheap wire found

  ftregan • 06/30/2014 at 08:56 • 0 comments

  After I tried many different options (magnet wire, heat shrink on bare wire, ...) the solution is, in the end, rather simple: Stranded wire is ok if you glue it with cyanoacrylate. Just buy 10m of wire from ebay ($1.49), and use a black permanent marker to make the black wire you may want.

  Ok, if you do lot of electronics, you can also buy two spools of 1000ft 30 AWG single core wire from ebay at $8.50 pieces. For this project you will use about 30ft, i.e. about $0.25 from your stock.

• Testing the fastech piezo

  ftregan • 06/29/2014 at 18:04 • 2 comments

  I made some test with an attiny13a and the piezo I bought from fasttech : the good new is that the piezo are easy to solder, and worked on first try. The sad thing is that sound is not really loud. It is better to run the mCU at 5V than at 3.3, but cheap cell coins does not come in 5V...

  I started to thing about how to handle a 4 tones polyphonic sound generation for a keyboard that can start 14 different notes... I guess I will have to use 4 piezo, or use resistors and a voltage divider to simulate an analog output.

• Piezo discs

  ftregan • 06/12/2014 at 04:43 • 0 comments

  After long long search,  I finally found 20 piezo disc ont fasttech for $1.25. You get 5 of them for that price, shipping included :)

• Cheap wire?

  ftregan • 06/06/2014 at 09:33 • 0 comments

  I need some wire.

  The TQFP package for the mCU has 0.30 to 0.45 wide pins, with a 0.8mm pitch. Awg30 wire seems ok and is standard so should be cheap. Rigid wire would be better so I can bend it.

  "wrapping wire" can be bought on aliexpress for $9 for 300 meter (edit : found it for 5€ shipped). That's dead cheap but buying 300 meter for my cheap project is cheating. People sell it on ebay at about 1.50€ for 5 meters. But for some design reasons, it would be cool to have both black and white wires. I don't want to pay more for the wire than I will spend for the mcu and the piezo!

  I have some alternative solutions:

  -Find something that looks good and is sold by the meter in a local store (cat 5 or telecom cable seldom have full black and full white wires)

  -Use only white wire

  -Use enameled copper wire (I could not find cheap 0.3mm one, but I can use several strand of 0.1mm wire, spools founds for $1)

  -Jumper wire sometimes can be bought for cheap on auction. They are only 50mm long, but I can solder them

  -Ask some ebay seller to send me 2x2m of wire instead of 5m one color for the same price

  I did not calculate how much wire I needed yet. let's estimate 12x80mm for the keys... 1 meter each color is enough.

  After I searched for one hour, the best search on ebay seems to be UL1007. You will find imitations of Kynar UL1007 wire. Unfortunately, it is a flexible wire, but that seems to be the best option if I want to stay cheap. Searching "single core" lead to a wire which would be perfect for me. 300 of it is cheaper than 300m of UL1007, but nobody seems to sell it in 5 or 10 meters legnth. I searched of UL1422, UL1423, and "airline awg", but only found 305m rolls.

  I don't know what to do: buy two spools of single core wire for 9€ both seems great, I will have 600m wire for cheap, but that would not match the project's goal.

• Choosing the mCU

  ftregan • 06/06/2014 at 07:52 • 0 comments

  I want an mCU that:

  -can drive a piezo speaker (most will)

  -has enough gpio to detect at least twelve keys (that's twelve gpios, maybe 8 if multiplexing)

  -is easy to find for cheap

  -run on internal oscillator without any external component.

  Atmega8 is a good candidate, can be bought for $0.90on aliexpress  if you buy 10. But buying 10 is cheating. It can also be unsoldered from a $2.35 avr usb programmer, or an arduino pro min can be bought for $2.72

  I found an Atmega8A on ebay for 1.04€. Ended auction don't seem to get lower than that.

• The idea

  ftregan • 06/06/2014 at 07:26 • 0 comments

  This project idea came when I wander what are the different mechanisms used to make animated popup cards. I found a (french) blog with rather good descriptions and in the middle of this page some simple technique was illustrated by a lovely piano designed by Maria Voctoria Garrido.

  This did not look like a good start for a hackaday.io project... Until two tenths of second later, when I feel like I needed to put some aluminum foil behind the keys to turn them into capacitive touches.

  Paper, glue, aluminum foil: all this is "free". How cheap could I make it?

  -Is a CR2032 battery enough to power it?

  -Could the battery holder be made for free from paper ?

  -What are the requirements for the mCU ?

  -Can the piezo discs be bought for under a dollar ?

  I hoped to stay below 5€, but finding cheap and good looking might be harder than I expected.

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