The Circuit

Below are links to the circuit diagrams for the Libre Tag system:-

The main diagram showing the Gun, sensor and power supply
Libre Tag Circuit – Rev A

Parts List

Name Value
R1,R12,R13,R15,R17 1K
R2,R3,R4,R5,R6,R8 10K
R7 20K
R8,R9,R10 100
R11,R14 20K
C1,C2 100uf
C3 10uf
Q1,Q2,Q3 BC548
Q3,Q4 Logic Level FET
XU1 LE50CZ LDO REG 5V 0.1A
IR LED An Infrared LED
LED 1 Hit LED
LED 2 Muzzle Flash

The IR LED needs to match the wavelength of the IR recievers. These two parts below from Rapids are what I have been using and suit each other well:-

http://www.rapidonline.com/Electronic-Components/Optoelectronics/Infrared-Devices/Matched-T1-frac34-infrared-emitter-and-detector-pairs/29406/kw/58-0442
http://www.rapidonline.com/Electronic-Components/Optoelectronics/Infrared-Devices/Infrared-photo-modules-38kHz/71292/kw/55-0901

These exact part numbers may not be available from your  supplier. The 3 main things you need to check are:-

  1. As above the wavelengths of the IR LED and Receiver must match
  2. The viewing angle of the IR LED needs to be suited to the focal length of your lens. A half angle of 10 degrees works quite well with a 50mm lens
  3. The LED needs a pulse power rating of a couple of amps

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