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this circuit features automatic exit entry delays a timed bell cut-off. it has provision f both nmally-closed nmally-open contacts, a 24-hour personal attack/tamper zone. it is connected permanently to the 12-volt supply its operation is "enabled" by opening sw1. by using the expansion modules, you can add as many zones as you require; some all of which may be the inertia (shock) sens type. all the green leds should be lighting befe you open sw1. you then have up to about a minute to leave the building. as you do so, the buzzer will sound. it should stop sounding when you shut the do behind you. this indicates that the exit/entry loop has been successfully rested within the time allowed. when you re-enter the building you have up to about a minute to move sw1 to the off position. if sw1 is not switched off in time, the relay will energise sound the main bell. it will ring f up to about 40 minutes. but it can be turned off at any time by sw1. the "instant" zone has no entry delay. if you don't want to use n/o switches, leave out r8, c8 q2; fit a link between led 3 c7. the 24 hour pa/tamper protection is provided by the scr/thyrist. if any of the switches in the n/c loop is opened, r11 will trigger the scr the bell will ring. in this case the bell has no time limit. once the loop is closed again, the scr may be reset by pressing sw2 temparily interrupting the current flow. the basic circuit will be satisfacty in many situations. however, it's much easier to find a fault when the alarm is divided into zones the control panel can remember which zone has caused the activation. the expansion modules are designed to do this. although they will wk with the existing instant zone, they are intended to replace it. when a zone is activated, its red led will light remain lit until the reset button is pressed. all the modules can share a single reset button. the stripboard layout of the prototype is available.
