A LaserTag System (Part I)
Basically, a lasertag system consists of two major components: an encoded laser signal generator which sends a laser beam out, and a light-sensitive decoder which detects laser emission. Such systems gain wide applications in marksmanship, precision guidance/control technology, and communications. In the older day, nostalgically this would be a challenging project for electronic hobbyists as the entire system could be built on electronic parts alone. Being an electronic enthusiast myself, I am going to devote this part presenting the wonder of electronics and circuit construction for such laser tracking system. One has to be aware of the potential hazard in laser projects. Laser beams could cause great harm to human eyes. Therefore no one should look directly into laser beams for any period of time. Neither it is safe to point a laser beam at others' eyes. There are always goods and bads in anything depending on how we make use of them. We could only reap the fruits of technology if we act responsibly and sensibly.
Encoded Laser Generation
On the laser signal generator side, I use a $2 laser pointer as the source of laser beam. The laser beam produced is fully focused and could easily reach up to a range of 30 feet! Notice from the circuit diagram Figure 1 that the laser pointer is powered directly from the power source through an array of not gates. This is a necessary arrangement to prevent draining heavy currents from the outputs of the control chips. Another safety precaution to avoid over-exposure of laser I introduced is a monostable timer circuit to limit the on-time of the beam to just a fraction of a second. The generated laser beam is then encoded through the dedicated encoder, the MC145026 IC produced by Motorola . This device is designed to be used as an encoder/decoder pair in remote control applications. The chip encodes nine lines of information which in our case, 4 bits data and 5 bits addresses, and serially sends this information upon receipt of a transmit enable (TE) signal. The words are transmitted twice per encoding sequence to increase security. For the sake of simplicity, only D6 of the encoder is jumpered to high which means that gun sends a serial 0001 data out as its trademark output. A decade counter is used to record and display the number of triggers. Notice that D0 and D9 of the counter are not used as indicators. The former is ignored because it corresponds to the initial reset condition while the latter is used to restart a counting sequence by resetting the counter chip. As a result, we have a total of 8 led tallies for 8 shots in a game. While the SCRs in the indicator circuits latch the counter leds thus showing the number of shots available, the reload button could manually override the counter any time and turn on all the tally leds to start a new session. I also use a buzz module I retrieved from a cheap toy to complement sound effects on the trigger.
Owing to the strong intensity and the focus power of the pointer, the laser transmission could be easily detected by any common photo-sensitive transistors without extra stages of amplification. The MC145027 decoder receives the serial stream and processes the data. The valid transmission (VT) output goes high on the MC145027 when two conditions are met. First, two addresses must be consecutively received (in one encoding sequence) which both match the local address. Second, the 4 bits of data must match the last valid data received. The active VT indicates that the information at the Data output pins has been updated and registers a hit. A similar decade counter as in the transmitter circuit is used to tally number of hits. Again like the transmission stage, the output bits of the decade counter are latched through the SCRs until the reset button i pressed to erase the tallies. The dual timer adds an siren sound effect to announce target hits. The single monostable timer circuit is to define a time interval to differentiate successive strikes received by the target.
The project could be easily modified for multiple players. Through the encoder, the generated laser beam is encoded as a 4-bits signal. Theoretically the encoder offers 16 different combinations of signal to be transmitted. For ease of circuitry and simplicity, I just use the individual data bits to distinguish between different signals. Therefore up to 4 signature laser transmissions could be readily achieved by duplicating the same transmission circuit using the D6, D7, D8, D9 respectively for different players. On the receiving side and depending on the number of players, the D6, D7, D8 and D9 could be correspondingly coupled via an AND gate to a unique decade counter circuit to complete hits tally registry for individual players. Multiple targets could also be achieved under the same principle. With 5 binary bits to represent address codes, 32 targets are possible. In fact the complementary action of the encoder/decoder pair makes remote control highly easy and flexible.
It did not take me long to build the entire project. The circuits are simple and straightforward. I tested my prototypes on breadboard and got them working in half an hour. By making use of modules I retrieved from toys I found in dollar shops I saved considerably construction time. It is certainly not a bad idea to spend some time in those shops to browse for things that might offer you project ideas. You may be surprised at how much bargain you could make. At the cost of a handful of dollars, it may save you hours of work if you have to build them from scratch. It is advisable not to disassemble the laser pointer completely for fear of ruining the focus structure of the laser. I cut the lower two-third of the pointer case off with a pair of pliers and left the top end of the pointer intact. It was then small enough to be fitted into a toy gun hulk.
This project could provide hours of game and sports for kids. Moving or rotating targets could increase difficulty levels of marksmanship. Other than shooting fun, the lasertag system could also be employed for guided systems or control communications with pinpoint accuracy. The marvel of it all is that these could all be done electronically at a few dollars!