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Rough Science 5 Zanzibar: Jonathan Hare's diary: Call of the Wild

Updated Wednesday, 2nd March 2005

Jonathan Hare's diary about the challenge for the Call of the Wild programme, part of the fifth BBC/OU TV series Rough Science, based in Zanzibar

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Jonathan and Ellen Copyrighted  image Icon Copyright: Production team Day 1

The idea of this challenge is to make a hydrophone to allow us to hear the sea creatures under the water. A hydrophone is basically a waterproof microphone, instead of picking up sound waves in the air it picks up sound generated pressure waves in the water.

The heart of the solution to making the hydrophone is a wonderful collaboration between the chemist and the physicist. Mike B, our chemist, is making some piezoelectric crystals. These have the property that they generate electricity if pressure is applied to them. If the pressure is high enough quartz crystals can generate 1000s of volts and make a spark. These are to be found in cigarette lighters and gas oven lighters.

The piezoelectric crystals Mike made are softer than quartz and although they will not be able to generate very high voltages they can produce voltages with less pressures. The idea is to take one of the crystals and fix it to a diaphragm. When sound hits the diaphragm from the air or when in the sea, it transfers the sound vibrations into pressure waves in the crystal. These make the crystal generate electricity and we have the basis of a microphone or a hydrophone.

Today I make up a simple amplifier from old radio parts and get the thing working live on camera which was a bit of a eureka moment. Make up a box for the loudspeaker so that it sounds better. Now I have to wait for Mike B to do his magic with the crystals …

Rough Scientists on boat

Day 2

This was a really great Rough Science day for me. Mike made some really fantastic crystals which I will be able to use straightaway. For my first attempt I would use an old (opened) tin can as the basis of the hydrophone. The bottom metal lid was used as the diaphragm. A crystal was attached to the centre and I made a little pre-amplifier out of one of the transistors from an old radio, so that its signal could be sent to the loudspeaker amplifier.

The first test runs were really great!! I had Kate talking into the tin can and you could hear her loudly through the speaker. Also dragging the tin can across the rough table surface made a really nice noise showing it was coming from the can.

Had a problem with the cable connecting the hydrophone to the amp. It developed a fault and it took ages to find what the problem was, I felt like I was losing valuable time.

My eureka moment for the day (perhaps of the whole series) was to realise that if I fixed the back of the crystal (rather than leaving it free) it meant that the vibrations on the can lid would squeeze the crystal more effectively. By simply using a piece of plastic to rigidly fix the back of the crystal I got perhaps 100 times more signal – the sound came right up!

Ellen gave me a plastic water jar (used for painting) as a container to put over the end of the apparatus to waterproof everything. We glued it all up and hoped that no water would get in. Apart from the obvious fact that sea water and electronics don’t go well together there is also the problem that the crystal would dissolve in sea water!

Day 3

Decide to test out the hydrophone in the water tank with a ringing alarm clock in a plastic bag! As I lower the two into the water I concentrate to see if I can hear anything at all from the hydrophone, which I do. I look up and the camera crew and sound men are trying desperately to be silent while wetting themselves laughing, tears running down their faces – they told me that this scene was one of the funniest things they have had to film!

I re-do the sealing around the hydrophone. We then all go off on the boat and I am a bit anxious because I haven’t had time to test the seals on the hydrophone properly. As it turns out the hydrophone works! I see a few fish around and hear their clicks. Not very spectacular but working none the less.

I make a silly mistake. In order to try and get the most sound from the device, I lower it in as far as I can. Obviously this increases the water pressure and in just a few minutes there was a horrible crackle and then no noise at all – water had got in.





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