Self-Made Laser Tag

We all have played the laser tag game at various fest or amusement parks. This laser tag is suitable for two player but can be easily extended to more number of players. Another advantage of this system is that in place of conventional infrared light used in commercial system, real lasers are used. In simpler terms it comprises of a laser blaster, base station, and shot detection vest. Every blaster comprises of an RF transceiver, an LCD, a sensor, and a laser. The laser is used to fire at other players on the press of a button. A RF transceiver is also used to send and receive any information about the game. Each blaster is also equipped with a photo-transistor to determine if the blaster itself has been hit by another player. An ATmega644 is used along with a self-made laser driving circuit to drive the laser. A real timer kernel is deployed on the MCU as it allow one to easily manage the main tasks and control how often to run them, as well as to provide certain tasks… Continue reading

Simplest RFID tag on AVR

This is real electronics porn. Simply speaking RFID tag is built by using AVR Attiny85 and small inductor. The power pins of AVR aren’t connected at all. It works, but how? Secret lies behind nature of IO/O pins of AVR. Coil connected to input pins power chip itself via clamping diodes. Once power problem is solved there is one more – chip clocking. Because voltage is too low to start chip internal oscillator. So coil also is an external clock source. This is why it has to be connected to AVR clock input. As RFID frequency is 125kHz so the AVR is also clocked at this rate. Firmware also has to perform on edge of resources. Probably to have reliable operation you would add couple capacitors and bigger coil. In other hand this is great hack showing how low can AVR go. Continue reading