Archive for December, 2009

New Video

Thursday, December 31st, 2009

I’ve just uploaded a new video showing two Libre Tag guns, one shooting the other.

Circuit Diagram Posted

Thursday, December 31st, 2009

I have posted the circuit diagram for the current version of the Libre Tag system:-

Adjustable Power

Monday, December 21st, 2009

Since I first built a working circuit for the LibreTag project, I always found that testing indoors proved to be without any need of aiming. My walls are white and so much IR is generated by the IR LED,that you can almost point the gun in any direction and score a hit.

I have been thinking of ways to be able to scale the power output of the guns down depending on where you intend to use them. My best idea so far was to use another FET to switch the IR LED either through a ~100 ohm resistor or straight to ground, to give a x1 or x1/10th power selection. However the problem with this is that it would never give you a chance to say scale from a large room to a small room.

Tonight I had a brain wave. After glancing over the data sheet for the 38khz IR receivers I noticed that they have a fairly high drop off as the frequency diverges from 38khz. I wondered if I could use this to my advantage by changing the PWM frequency of the transmitting IR LED.

IR LED response curve

I am happy to report it works wonders. I still need to implement a menu option to make the “strength” selectable, but with the freqency set to 50khz the sensitivity of the receiver, as per the graph, drops down to about 20%. It makes the gun usable indoors, with no sign of any reflections. It is maybe a little too under powered at 50khz, but this can be tweaked.

Progress Update

Monday, December 7th, 2009

Work has been progressing rather slow recently. I’ve been very busy and just haven’t had the time to do some serious work on the guns. Coupled with the shorter days and awful weather we have been having in the UK the last few weeks, means I havn’t had a chance to go outside to do wood work / painting.

However I have more or less finished one gun now, with another 2 not far behind.

As you can see I’ve painted them with a large red side, this is so they comply to the VCRA (Violent Crime Reduction Act). It sad that we have to do such things, but better safe than sorry. I have also been experimenting with different types of sights and have attached a prototype one to the gun. It seems fairly accurate, I was easily able to aim perfectly from over 100ft. I will be testing some other types of sights in the coming weeks and hope to post a article comparing them.

The last two pictures are of the sensor. It is mounted in a Tic Tac box, which seems to be a pretty good fit. There will eventually be 3 sensors per gun, but I need some more people to eat Tic Tacs first.

Code wise, not much has changed. I have tidied up some of the code and made a few corrections to the parity encoding/decoding which has reduced the number of corrupt virtual bullets. It seems good enough now, with only one being received every 30-60 shots.