Circuit Scribe is a really neat kit that uses conductive ink in drawing your own circuits. This is really cool because it allows you to doodle your own circuit board! In the following steps, we are using the "Developer Circuit Scribe, Draw Your Own Circuits" 48 piece set. The kit comes with magnetic modules (power, photo sensor, NPN transistor, motor) that connect to the lines you have drawn and create a circuit. The following Instructable will detail the creation of a motor circuit with the addition of a photo sensor.
Step 1: Understand the NPN transistor.
The NPN transistors primary use is to amplify a current. Small current between the base and emitter is used to control a larger current between the collector and emitter. The photo shows how the NPN amplifies a signal.
The NPN transistor can be used to run modules that require higher current loads, such as the motor in this example.
Step 2: Understand the photo sensor.
The photo sensor is similar to the NPN transistor, only the current is activated by light. When power is applied from the battery and light is shown on the sensor, the output current increases. Fading the intensity of the light works as a dimmer switch would, and slowly decreases the current.
Step 3: Observe the connection paths.
In order to control the motor using a photo sensor, we need to amplify the sensor output. The NPN transistor does this by directing a large current from the collector to emitter, and a small current from the base to the emitter. The collector current comes directly from the motors output, while the base current comes from photo sensor output.
Step 4: Fill in the current lines and attach all modules.
The workbook provided with the kit will show where exactly to fill your lines with the conductive ink. The diagram is fairly comprehensive though, so it's possible to create these circuits without the workbook.
Fill in the lines, connecting where each of the modules will be set.
Step 5: Turn it on and test it out!
Aforementioned, the intensity of the light should work as a dimmer to the current capacity. When the light shining on the photo sensor gets brighter, the motor will spin faster!