GB1509562A - Gun and target apparatus utilising a light signal - Google Patents

Abstract

1509562 Optical position finding METTOY CO Ltd 26 March 1975 12738/75 Heading H4D A gun and target apparatus takes the form of a pulsed light transmitter mounted on the gun and an associated photosensitive receiver circuit which detects the pulsed light signal from the gun transmitter when gun is pointed on target, and operates an alarm or similar responsive device. As described the transmitter, Fig. 1 comprises a multivibrator 10 the base voltages for which are controlled by timing circuit 11. When the trigger switch 15 is pulled C3 charges through resistors R 1 and R4 which turns on the multivibrator 10. When the capacitor is approaching the fully charged state the frequency has slowed down and oscillations then stop. The output from the multivibrator drives light source 19 via transistor TR3. The light source may be an infra-red diode or may emit visible light. The result is a transmitted light pulse at approximately 1000 Hz for 1 second. The receiver, Fig. 2, is mounted at the target or may be mounted on the gun with a corner reflector mounted on target to retro-reflect light to a receiver mounted on the gun. Light-dependent transistor 25 may be solely mounted at the target and the rest of the receiver circuit housed separately. Photo-transistor 25 is biased by circuit comprising transistor 26, resistors 27, 28 and capacitor 30 so that the collector emitter voltage thereof is kept constant despite changes in collector current due to changes in ambient light conditions. The reduction in output impedance in the first stage produced by capacitor 30 at frequencies at or above the transmitted light signal allows high-pass filtering of the desired signal which is fed through amplifier 21, buffer stage 22, diode pump 32 and 33 and a transistor 35. Detection of the wanted signal triggers S.C.R. 38 to operate, e.g. relay 39, which operates a visual or audible indication that a "hit" has been scored.