contact mic

Bigger, Harder, Stronger, Homemade Piezoelectric Crystals

Thursday, August 25th, 2011 | Building Things | 3 Comments

Had a bash at making larger Rochelle Salt crystals using this method. Initially used too much water and nothing formed overnight. I reheated the liquid and added more Sodium Carbonate until milky, then added Cream of Tartar until it went clear again. Seems like the larger bowl I formed the crystals in coupled with the slightly stronger liquid worked a treat. Most of the following are about 3-4cm in size.

Click to enlarge….

 

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Announcing my intention to do a Weekly DIY Music Thing…

Err yep, I’m going to post a new project that you can make at home, every week starting now. My last post about making Piezoelectric crystals at home seemed to be something of a hit getting featured both on hackaday.com and CreateDigitalMusic.com so I thought I’d give you more of what you like while building a sample library for my own compositions.

I thought of covering:

  • Contact microphones – construction and creative usage
  • Simple electronic music circuits – warm up your cmos chips
  • Prepared instruments
  • Max/MSP usage – Maybe some generative stuff?
  • Arduino
  • DIY music controllers
  • Studio techniques

If you have any ideas please comment here and I’ll try and cover them. Keep your ideas simple and doable in a 5 min video!

Next time you see the soldering iron logo there will be a tutorial under it.

Take care,

John.

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Real Sound Cookery – Make a contact mic with baking soda and cream of tartar.

home made Potassium sodium tartrate "Rochelle Salt" crystals chunk in top right is aprox 5mm long

I’ve been into contact mics for a very long time, and have used them to record sounds for my records since 1999. There is something magical about how an innocuous little brass disc covered in ceramic piezo crystals can act as a sonic microscope, revealing tiny sound-worlds easily and cheaply. For a bit more info on contact pickups have a look at some of my previous posts: Shit I’m a Geek / The joy of Piezoelectricity and Leafcutter’s DIY Steel Can Hydrophone & Preamp. Step-by-step guide *schematic link fixed!*

I recently stumbled on a great video tutorial by Collin’s Lab entitled  ‘Homebrew Piezo’ in it he shows how to make Potassium sodium tartrate  crystals also known as “Rochelle Salt”. These crystals are fairly amazing in that they are made from ingredients available cheaply from your local grocery store or supermarket. I suggest you watch it as it shows the process really clearly. Later in this post I’ll show my experience of following Collin’s method and do something Collin didn’t – Made some sound with it!

If you want to make your own crystals you’ll need:

  • 200 g / 7 oz Cream of Tartar (aka Potassium Bitartrate, aka potassium hydrogen tartrate) from the grocer/supermarket
  • about 120 g / 4 oz Sodium Carbonate  (aka soda ash) OR same amount of baking soda (Sodium Bicarbonate) if you cant find the Sodium Carbonate.
  • Pyrex jug or bowl
  • Pan big enough to fit the bowl inside
  • Filter paper or Kitchen towel
  • Thermometer useful but not essential
  • Clean Baking tray and Oven if you are using Baking Soda instead of Sodium Carbonate

The Method is pretty simple, follow Collin’s Video to the letter! If you cant see the video for some reason here are the basic steps:

Collin asks for Sodium Carbonate  (soda ash) in the video, I could not find this but luckily you can make it very easily. Get hold of some Sodium Bicarbonate from the chemist or supermarket and spread it thinly on a clean baking tray. Now bake this for an hour or so at about 150 deg C / 300 deg F stirring the powder every 15 mins or so. Doing this will give of water vapor and Carbon Dioxide (open a window maybe) and after an hour your Sodium Bicarbonate will have turned into Sodium Carbonate!

  1. Using your Pyrex jug Dissolve 200 gr / 7oz Cream of Tartar (Potassium Bitartrate) into 1 cup cold water. Stir.
  2. Pop the jug into a pan of water, turn on the heat until the water bath reaches about 82 C / 180 F. If you don’t have a thermometer the water will start simmering at this point so keep an eye out for little bubbles in the pan.
  3. When the water bath is at 82 C / 180 F put half a teaspoon of Sodium Carbonate into the Pyrex jug and stir, it’ll bubble up and then subside.
  4. When the bubbling subsides repeat step 3. until the milky mixture goes clear (slight yellow tint).
  5. Your mixture is now ready to filter, while still hot pour into another heat proof container (a clean jam jar is good) through filter paper or kitchen towel to get rid of any solids. Don’t mess about here as crystals will form as soon as the mixture cools and you don’t want that happening in the filter.
  6. Place the container in a coolish spot cover loosely and wait for the crystals to form!

This is my solution just after pouring:

 

tiny crystal forming at the botom of the jam jar

 

after 2-3 hours

after sitting overnight

loose crystals fished out of the jar dried and viewed X50

So I seem to have generated thousands of tiny crystals as opposed to a few big ones like Collin managed – not sure why this happened but maybe linked to a fairly short cooling time. I wanted to see if the crystals were in fact piezo electric so I arranged the following rig to hold the tiny crystal against two contacts which were connected to a little battery powered guitar amp.

.

Holding a music box against the clamp I was able to record this sound

Not quite as good as the stuff in my mic drawer but it’s amazing considering it’s made from cookery ingredients!

I’m going to let the crystals in the jars carry on growing and I’ll add another post when I’ve managed to grow a bigger crystal.

Give it a go and let me know how you get on!

J x.

UPDATE – Check out my larger crystals.

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Shit I’m a Geek / The joy of Piezoelectricity

Sunday, July 26th, 2009 | Building Things, Electronics | 16 Comments

For some reason I have become completely obsessed with electronic circuits in the last couple of weeks. Maybe it’s because I bought a semi-decent soldering iron for the first time and realised that it’s very satisfying to make nice shiny connections. I think i’m headed toward a life breathing in the heady (and no doubt toxic) vapor of solder fumes.

Anyway I know next to nothing about building electronic circuits so it’s been a bit of a challenge to pick up the basics. I’ve been studying Ohms’ Law, and working out how to interpret circuit diagrams, while I was looking for information about audio circuits I stumbled on an interesting first project.

Introducing Alex Rice’s Piezo Preamplifier

If you click on the link you’ll find a schematic and lot’s of notes on component selection and construction and interesting information on how the circuit actually works. I must say that I don’t understand all of it but I thought it looked like a useful circuit to have.

First a little about Piezo discs….

£0.14p Piezo Disc - attach a jack lead and you have a Contact Pickup!

Piezo discs are fantastically cheap and interesting things, they are like sonic microscopes and allow you to to make very simple ‘contact pickups’ which can be pressed onto objects to probe for hidden sounds. I have used them constantly since I discovered them about 10 years ago. I used them a lot to record mechanical sounds for my 2003 record Microcontact. Here a Zip disk gives way to a mechanical breast pump…

 

if it sounds half as good as it looks.....

Looks like this....

Sounds like this….

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Over the years I have used piezo discs to:

 

In a hydrophone....

listen underwater....

 

record the slinky...

record the slinky...

 

and hear ice melting.

and hear sound of ice melting.

Brilliant as Piezo’s are my interest in them had started to wane a little in the last couple of years. Things recorded using them tend to lack bass and often sound a bit thin. Alex’s Circuit addresses the problem of impedance matching the Piezo disc and the audio input (which helps counter bass loss). He also promises ‘to make piezo contact microphones sound awesome’ which has to be worth a go!

Alex’s circuit is very simple with just 12 components but given my complete lack of knowledge in this area it took me a couple of days to make sure I knew which were the right components to get. I ordered from Rapid and true to their name the parts arrived in a few days. I first tried to build the circuit on a proto-board which allows you to prototype circuits without soldering. When tested the first version it was very noisy and had a lot of 50hz hum. I had another shot at the circuit and because I was finding it hard get my head around translating the schematic to the the proto-board got very confused indeed. I decided to have a break and then take the plunge and solder the parts onto breadboard figuring that it might sound better as the components would be better connected. After a hour or two I had this:

Phantom powered piezo pre-amp

My first circuit - Phantom powered piezo pre-amp

Thankfully again it failed to explode and sounded much better on the bread board. There was still some hum and interference which went away when I shielded the board using a little metal tin box.

Here is a recording made with the Piezo stuck onto a Kalimba

Audio clip: Adobe Flash Player (version 9 or above) is required to play this audio clip. Download the latest version here. You also need to have JavaScript enabled in your browser.

And one of my watch ticking (very quietly)

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The pre-amp sounds pretty good, amazing really considering the components excluding cable and XLR connector cost under £2.00. The recordings with the pre-amp sound much fuller than without and I’m sure the noise you can hear in the watch recording would be reduced if I had matched the FETs as it says you should in Alex’s instructions.

I’m really pleased with my first circuit and have learned a lot. I wonder what I should try and build next?

before I go here are some links that I have been using to learn about electronics.

Alex’s Site has disappeared but his preamp remains!

All About Circuits

Java Circuit Simulator

And before I go have a look at Alex’s miniaturised  Piezo preamp which fits inside an XLR plug. It must be 1/6th the size of mine.

 

amazing!

amazing!

Take care!

Leafcutter John x.

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