Laser Tripwire with Photoresistor

Theory:

This time we're making a laser trip wire. These usually turn up in action movies and the idea is that an alarm goes off if the laser is broken. For this lesson, we are creating these trip wires in order to detect unauthorised vehicles inside our National Parks and Wildlife Reserves. If there is a large vehicle entering the area, we'll send a message to the park rangers and they will go and find the intruders.

However, our laser can't actually tell if the laser is broken - it's just a light. That's why we're using our photoresistor. If you recall from a previous week, our photoresistors sense the amount of light. The darker it is, the higher the number.

To create our trip wire, our laser is going to be pointed at the top of the photoresistor. When something passes between the laser and the photoresistor, the photoresistor will register a higher number and send a message to another microbit via the radio.

On our other device, we have a passive buzzer module and a LED. We've used the passive buzzer before so wiring that should be straightforward, but the LED is a new component. On the diagram, our LED has a straight leg and a bendy leg. On a real LED, the legs of the light are different lengths. The bent side of the LED as seen on the diagram stands for the long leg of the LED in real life. Connected to the long leg is a resistor.

The resistor acts as a way to adjust the amount of electricity in a circuit like taps do on your kitchen sink. It's brown on the diagram, but it's blue in your kits. Connect one end of the resistor to the long leg of your LED. Connect the other side of the resistor to a wire that ends at P1. Make sure you have a wire connecting the short leg of the LED to the Ground rail (the blue rail).