Play dough circuits
First you need to make your dough. You will need salt play dough |
Cute little illuminated sculptures is where we're heading, but let's get started with some basics. You'll need a few light-emitting diodes, a battery pack, and two types of play dough: ordinary conductive play dough, which you can buy or make yourself (see instructions below), and non-conductive play dough, which you'll need to make (see instructions below). |
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Light-emitting diodes (LEDs) LEDs are cheap and they're available from most electronics suppliers. The flexible legs make them perfect for poking into play dough. Grab a variety of colours while you're there. |
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Batteries To power the LEDs, you need a 4 by AA battery pack. You'll need to solder terminals onto the leads for better electrical contact with the play dough. All these parts are available where you buy LEDs. And, who knows, they might even solder the terminals on for you. Doesn't hurt to ask, right? |
How to make conductive play dough
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1.Ordinary play dough from the toy store conducts electricity and works fine, but you can also make your own with this standard play dough recipe. In a saucepan, completely dissolve half a cup of salt in 1 cup of warm water (dissolving the salt first ensures a good texture). Add your favourite food colour. Next, add 3 tablespoons cream of tartar, 1 tablespoon of vegetable oil and 1 cup of plain flour. Stir thoroughly. |
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2. Cook the play dough mixture on low heat, stirring constantly with a wooden spoon until a ball forms (it takes just a few minutes). Place the ball and flatten it out on a lightly floured baking tray to cool (again, just a few minutes is enough). |
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3. Knead in more flour until the dough stops feeling sticky and you're done. Like play dough from toy stores, this batch will conduct electricity nicely. |
How to make non-conductive play dough
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1. Use demineralised water instead of tap water if possible (available from supermarkets and grocery stores). Mix 1 cup of plain flour and half a cup of white sugar in a mixing bowl (caster sugar works even better). Add 3 tablespoons of vegetable oil and mix thoroughly. Now add one tablespoon of water at a time until the dough forms baked-bean sized clumps. |
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2. Transfer the lumpy dough onto a baking tray (not floured yet) and knead into a ball. Add more water, one tablespoon at a time and knead. Continue adding water until the dough becomes sticky. Now knead in more flour until the ball stops feeling sticky and reaches the texture of play dough. |
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3. The non-conducting dough isn't quite as 'smooth' in texture, but can still be sculpted and rolled like normal play dough. Most importantly, it won't conduct electricity at the low voltages we're using. Store this dough in the fridge when not in use. |
Making circuits
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A simple circuit Make two lumps of ordinary conducting play dough and poke one of the battery pack leads into each lump. Now poke one of your LEDs legs into each lump. Electricity only flows through LEDs in one direction so, if the LED doesn't light up, take it out, turn it around and poke the legs back into the lumps. |
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Short circuits While the lumps are separated, the only way for electricity to flow through the circuit is to go through the LED, so it lights up. Push the two play dough lumps so they're touching each other, however, and the LED stops shining because you've created a short circuit. The conducting play dough has much lower electrical resistance than an LED. In a short circuit, the electricity flows through the play dough and bypasses the more resistive LED. |
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Preventing short circuits Use the non-conducting dough to prevent the two lumps of conducting play dough from touching each other. The non-conducting dough has much higher electrical resistance than both the LED and conducting play dough, so now the electricity flows through the path of least resisance, which is through the LED. |
Now you know how to light up the LED, start experimenting and next time, I'll show you how to build and illuminate some groovy play dough sculptures.
What's going on?
Salty water conducts electricity, which makes ordinary play dough a reasonably good conductor. Sugary water doesn't conduct electricity nearly as well. Replacing the salt in play dough with sugar produces dough that conducts so poorly at low voltages that it functions like a non-conducting insulator. Normal tap water, however, contains trace quantities of dissolved minerals that act like salt. That's why demineralised water will improve the insulating properties of your non-conducting dough.Have the children write down the experiment with pictures in the last triangle on their page.
