On 3/28/2009 12:26 PM David spake thus:
"David Nebenzahl" wrote in message
s.com...
OK, so I'm trying to come up with a simple (maybe even
elegant) solution to a simple problem. Have an idea I
want to run by y'all.
Function: person has a motion-detector light installed
in their home. They want a buzzer/bell/annunciator of
some kind to go off *momentarily* whenever the light is
activated.
Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif
Why not take a crack at calculating the values of the
components and post your final circuit here. That way we
will get a good idea of how adept you are at circuit design.
I would still recommend putting R3 across C2 rather than C1
as per my original suggestion. That insures the drive to the
transistor truly goes to zero after some amount of time.
Hey, thanks for sticking with me. Check latest circuit incarnation at
http://www.geocities.com/bonezphoto/...e-shotBell.gif.
Component Value
-----------------------------
C1 100 uf/200 V.
C2 1 uf/100 V.
R1, R2 500 Ω, 2 W
R3 220 kΩ, 1/8 W
R4, R5 10 kΩ, 1/8 W
D1 1N4001
Q1 D1266 or equiv.
Rationale for values (assuming ~20 volt, 100 mA load):
C1: large enough to filter bulk of ripple
C2: sized for proper "on" time (WAG)
R1, R2: voltage divider to yield ~20 volts for load device;
calculations dictate 5 watt load, but since it's of short
duration, 2 w. should be sufficient
R3: bleeder (slow) for C1
R4, R5: this is also a WAG (wild-ass guess); see below
D1: 1A, 600 PIV
Q1: selected because I have these and have used them before.
OK, I admit that I do not know how to calculate those last 2 resistances
for proper biasing of Q1; so sue me. I do understanfd the general
principle of biasing; just never had the formal training to learn how to
calculate values to implement it. I'd appreciate your comments here, and
I'd be curious to know how far off my guesses were.
BTW, I misunderstood where you wanted the bleeder resistor.
So give me a grade on my work.
--
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