How you test your circuit will depend on the specific circuit you are building. In general, you should follow this procedure:
Double-check your circuit and the breadboard diagram to make sure all your components are in the right place.
Check what your circuit is supposed to do according to the project directions. Is it supposed to flash lights, make noise, somehow respond to a sensor (like a motion or light sensor), or make a robot move? Many Science Buddies projects will contain a written description and/or video of how your circuit should work.
Turn the power to your circuit on (for example, by sliding a battery pack switch from OFF to ON). If you see or smell smoke, turn off or disconnect the power supply immediately. This means you have a short circuit.
Follow the project directions to use your circuit (for example, shining a flashlight at a light-tracking robot, or waving your hand in front of a motion sensor).
If your circuit does not work, you need to troubleshoot (or debug, meaning to look for problems or “bugs” in your circuit). See the common mistakes that we have discussed in the previous topic.