Shrinky Circuit is a way to rapidly prototype circuit boards without the conventional PCB /chemical etching procedure involved. More Instructables on this method to come later.

Step 1: (Optional) Color

Color the Shrinky Dinks with colored pencil. Color on a single side should be enough if you are using the translucent shrinky dinks. Color both sides if you are using the white shrinky dinks. Note: that the color will look a lot darker than the colors before shrinking (See image for comparison).

Step 2: Circuit Design and Testing

It is often helpful to test your circuit and components on a breadboard before you insert component into the substrate because once the circuit is shrinked and you find that the circuit is breaking because of a faulty component, there's no going back.

Step 3: Trace, Then Cut Out the Pattern Along the Outer Traced Pattern

Print / trace pattern of your circuit design and the outline for the circuit shape with a pen.

Notes for surface mount LED (Optional) :

If you are using a surface mount LED instead of a through hole component, then you don't need to dig the holes on the component ends. Also, when tracing circuit pattern, the space that you leave for the LED should be 3 times the size of your actual LED to accommodate for shrinking. Using the through hole component enables more flexibility since the wires can bend.

It may be helpful to draw how the LED should be arranged by marking where the tick of the LED (negative end) should be faceing. In this case, they should all be facing in the same direction

(Image Source: phenoptix)

Step 4: Dig Holes for Through-hole Components

Using an exacto knife, dig a hole through where the components embeds into the circuit (i.e. where the lines connects to the components) . Make sure you remove the excessive plastic around the hole so that it doesn't clutter up during heating.

Step 5: Conductive Tracing

Trace the conductive line for the circuit with conductive pen leaving blank space for the surface mounts LED. Give it some time to dry. For powerpads and component holes, draw a round circle around the hole so that during heating a solder blob is formed around the component.

Step 6: Insert Components

Step 7: Heating

Oven bake (Preheat 5 minutes at 275F) or use a heat gun to shrink the substrate. Flatten the substrate before cooling. Generally, oven baking creates a flatter substrate than heat gun due to a more uniform heating. But heat gun can be used to generate more complex substrate shape because you can work the substance while heating.

Step 8: (Optional) Add a Switch

Place a conductive stripe of wire, conductive thread/ tape, aluminum or any conductive thing across the area denoted by the "Switch" component. Then the circuit is done!

Step 9: Test With Power Supply

Test with power supply on the powerpads. You could also insert a battery holder in the two powerpads before shrinking as a power supply.

Step 10: (Optional) Debugging

If your circuit is not working, it could be that the conductive pattern is not working somewhere in the circuit. Test sections on circuits with a multimeter for conductivity. If you find some region that is disconnected, you can patch with some conductive epoxy. Using the conductive epoxy, connect the LED to both sides of the conductive pattern. Leave the circuit sitting for 24hr for the Epoxy to dry up.