This is probably simple, but I'm not an ee.
A closet with 4 doors, each has a normally-closed pushbutton connected to 5V source on one end and (to the same) 5V relay which controls the 220V (AC) of the room lights. So the doors connected to the relay directly, not through a digital relay driver.
The problem : when either door closed, the door physically bounces, regardless of the pushbutton's electrical bounce.
And so I need to do around 0.75 second debouncing when the door gets closed (switch gets open), most circuits i see involves push-up/down resistors into TTL logic, which means i'll need to attach a relay-driver afterwards.. and this is what i'm trying to avoid.
How can this be done with passive parts ?
Thanks in advance.
Best Answer
Not passive parts, but nothing to be very scared of, one little 8-pin DIP chip and some passives.
simulate this circuit – Schematic created using CircuitLab
R1 is the timing resistor (in conjunction with C1). 75K will give you about 750ms.
R3 and R4 set up a timing reference of approximately \$5V \times (1- \frac {1} {e})\$ = 3.18V so R1 works out nicely.
C2 is a bypass capacitor
R5 adds about 1% hysteresis to prevent relay chattering
D1 absorbs inductive kick from the relay coil inductance
LM311 is an ancient bipolar comparator chip