canine defence

canine defence elektor december 1980 — 12-47 The canine defence is in two parts, first line defence and second line defence. The first is in fact operating permanently in the form of a flashing light. This will enable you to locate your pet can at night and has the added bonus of indicating to other humans that your can is alive and well. This part of the circuit uses the well known LM 3909 to flash an LED mounted in the top of the can. The value of timing capacitor C1 can be varied to alter the flash rate if required. The second part of the circuit is an alarm. When the can is tilted or in any canine defence ponents can of course be altered to suit the individual reader, although the din produced by the values given should be enough to protect most cans. A supply voltage of 4.5 volts is re- quired and this can be supplied by means of three HP7 batteries connected in series. Since the quiescent current drain is very low an on-off switch is not necessary and the batteries can be ...