The last step in creating the laser tag robots is to add the laser source and laser target, as well as the code that will let you fire the source and detect a hit on the target. First, you'll need to install the hardware.
Let's start with the laser source. You can just use a raw laser source, similar to the one shown in the following image:
They are inexpensive and available on eBay and other online electronics retailers. However, it is a bit easier if you get a laser source with a bit more supporting circuitry, as shown in the following:
These are also available from a number of online retailers, you can find similar modules. All you need is a way to turn on your laser with a control signal from Raspberry Pi. In this module, you'll connect the device to one of the open collector outputs on the motor controller board, the GND pin to OC1 pin, and the S pin to other OC1 pin connection, as shown in the following image:
