Could you please spare a moment and have a look at this circuit. Once Q1 is on, Q2 is biased off and it must stay off as long as Q1 is on. When reed sensor opens, Q1 turns off and a short pulse from C1, through Q2, turn the SCR on. The SCR is a sensitive type. This activates the relay. My question is, due to reed sensors being far and therefore long wire for connection, obviously there will be RFI/EMI issue, so what do you think about input protection C2,C4 and C5, arranged as low pass filter? please note R1 and R3 must be high value to minimise the current consumption from the battery.
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