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T O P I C    R E V I E W
a2nathan79 Posted - Sep 01 2009 : 3:06:59 PM

hi frens,i'm new here...i would like to build the following project.this circuit is designed to activate the relay for certain period time only. can anyone help me how to make the relay activated continuosly after correct pin code enter.

Description

Substitutions
C1 1 1uF 25V Electrolytic Capacitor
C2 1 220uF 25V Electrolytic Capacitor
R1 1 2.2K 1/4W Resistor
Q1 1 2N3904 NPN Transistor 2N2222
D1 1 1N4148 Rectifier Diode 1N4001-1N4007
K1 1 12V SPDT Relay Any appropriate relay with 12V coil
U1 1 LS7220 Digital Lock IC
S1-S12 12 SPST Momentary Pushbutton Keypad (see notes)
HD1 1 12 Position Header
2   L A T E S T    R E P L I E S    (Newest First)
Aaron Cake Posted - Sep 07 2009 : 10:23:51 AM
It looks like you are referring to the digital keypad lock.

Check the datasheet for the LS7220. It may have a mode that allows this and the only requirement would be bringing a pin high or low.

Failing that, the simplest possible way of achieving this is to use a DPST relay. Connect one of the sets of contacts across the transistor. This will essentially turn the relay into a latching relay and it won't drop out until power is reset.
pebe Posted - Sep 01 2009 : 3:45:40 PM
I don't see the circuit you refer to.

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