Well then by gum all the signals we need can be gotten w/o tearing the
dash apart! A little pcb, a handful of parts, and hey presto! we have a
idiot buzzer. Perfect for that man or woman in your life who wishes to
keep his or her on the road while driving.

--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR

On 12/16/2009 8:22 PM David Beierl wrote:

> At 09:19 PM 12/16/2009, Rocket J Squirrel wrote:
>> The Coolant Temp light on the 1.9 appears to have both ends going into a
>> magic box according to Bentleys. It may be that one side of the lamp is
>> tied high, or the other low, but without getting into the dash, it's
>> unclear: they may both be active wires.
>
> The temp light on all versions of Vanagon is a self-blinking 5 volt LED
> in series with a 5.1v Zener diode, driven by a timing circuit employing
> a 741 op amp. This circuit powers the LED for about three seconds any
> time the resistance to ground on the sender input falls to or below
> about 35 ohms (I don't know the voltage that represents but I'll find out).
>
> In practical terms it would be easier to essentially duplicate that
> circuit than to open up the gauge and get a drive signal from inside it.
> The circuit I'm envisioning would piggyback on the back of the gauge
> terminals (+10v, ground and sender input) outside the flexible circuit.
> It would have inputs from the other lamps which I believe are both
> switched-ground, wired-ORed with the temp-light-circuit. Might or might
> not need a buffer amp on the piezo drive.
>
> Yours,
> David
>