[AT] Electronics - WAY OT

[Spencer Yost]

Diagram URL again:

http://www.uoguelph.ca/~antoon/circ/headalrm.html


And the winner is:

>Howard R. Weeks wrote:
>
>...snip...
>I would try a couple different transistors at Q1.  If that doesn't work,
>try dropping the Q1 base resistor to something like 8K - you can probably
>go down to as little as 5K without hurting anything.  Lower value just
>turns
>the transistor on harder or pulls the collector closer to the emitter
>(voltage wise).
>

Transistor Q1 wasn't getting saturated or was "leaking"(I don't know the
right term for that).  I replaced it in case it was faulty - it wasn't
"leaking".  I then replaced the 10K R1 resistor with a 4.7 and the sucker
worked perfectly.

Honorable mention: Phil Auten and Bill Boyd
Bills advice was not as specific as to the solution (get Q1 saturated) but
his advice implied it.
One of the responses was a private reply from Phil Auten.  His solution was
to add another resistor in-line with the buzzer. Because I was already
close to the base voltage the buzzer would handle, this would have worked.
However, the buzzer would have been permanently softer too.

Close, but no cigar:
1 - Oil pressure based switch:   I can't turn off the buzzer by just
turning the key to "on" if I want.(ie using the headlight to work by but
don't want to have the engine running)
2 - Hot jump (two hots) a buzzer to dash lamp and ignition:   Would work,
but this is cross grounding.  Actually would end up being pretty safe on my
diesel where the ignition and dash lamp circuit are close to the same
rating and fusing but is not safe, or could be costly, with computerized
ignition on gas engines where the two circuits are usually different in
specification and fusing.

Final analysis:   My buzzer must operate at a lower voltage/current than
the buzzer the original schematic designer used; so the Q1 transistor was
not clamping hard enough for my buzzer.  However, parameters for the buzzer
aren't specified so I just had to guess.  I guessed wrong (-;

Thanks for all your input!

Spencer Yost
Owner, ATIS
Plow the Net!
http://www.atis.net