chris@zorin.UUCP (Christopher Nielsen) (09/17/90)
Well, I played with this stuff Sunday, and here is the result...
I started with Mr. Koch's suggestions. Using the PNP definately does work,
but the first part didn't work, that is, I couldn't get the 2N2222 to turn
on for more than a split second even with a 1M resistor. I think it's
because (I'm guessing) that the output of the 8155 chip sinks better than
it sources (typical, I believe...). With that, I decided to try placing the
cap. between the transistors, so that I could make sure that enough current
could be supplied. Anyway, to make a long story short... The circuit below
works, and I have it wired temporarily to the unlock relay.
By working, I mean it will unlock the door... But there are a few problems.
I hope Mr. Koch, or someone else can straighten me out!
First, there is a bad side effect. When I first apply power, the PNP gets
an initial pulse. I tried various resistors and other parts at various
points, but it didn't get better. I think it has something to do with the
cap. being at 0V (since power was off) when the +12 comes on.
Second, probably a bit harder... Since this is a RC circuit, and the PNP is
a linear device... guess what type of wave form the relay sees! A ramp,
or worse (AC?). Anyway, the effect is that instead of a nice, clean
klunk sound from the relay/door selenoids, I hear a klunk-buzzz. Now you
know why I wired my circuit temporarily. I am begining to take back my
comment to Mr. Swonger, about my not wanting to use a 555. Perhaps that
is the quick & dirty (and better) solution in this case... I thought a
simple RC would suffice.
_____ ,-----.---/\/\/\/\/-- +12
/ \/ C | 10K
B | | / | |
>--\/\/\/--|-|< | | |-------| E
1K | | \| |E | | | B | |--- +12 existing relay
\_____/\__. `--| |--/\/\/\/---| | ______ /
2N2222 | | | 100 | |__________nnnnnn___
| |-------| C `---|<------|
| TIP125 |
| (PNP darlington) -----
----- ---
--- -
-
Does anyone see any danger in the ramp waveform (or what ever evil)
going to the relay (and selenoids)?
Would this circuit (less the cap) be sufficient for flashing the parking
lamps?
Christopher A. Nielsen
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