nuckolls.bob(at)aeroelect
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 Posted: Tue Aug 27, 2013 11:06 am Post subject: Cessna dual electronic stall/gear warning horn |
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At 08:27 AM 8/27/2013, you wrote:
| Quote: | Hi Bob,
I wonder if you can help me with a problem. A partner and I recently purchased a 1977 Cessna 177RG which has a dual electronic stall warning and gear warning system which is only heard through the dual overhead cabin speakers. The stall warning is output through one speaker as a steady on stall warning, while the gear warning is output through the second speaker (slightly different tone) as an intermittent on/off gear warning. I find it difficult to hear the stall horn or the gear warning horn when wearing a noise cancelling headset. Question: is there a way to convert the electric output that drives the two overhead speakers into an electronic output which could be fed into a PMA8000BT audio panel? Perhaps there is a device I could interface between the dual electronic stall/gear warning and the PMA8000BT audio panel, or maybe this could be fabricated with relays and off the shelf electronic parts.
I checked with the audio panel manufacturer, PS Engineering, but they said it's not possible to convert an electromechanical warning into and electronic signal.
Thanks in advance for your advice Bob. |
HHHmmmm. . . . I think the PSE guys missed the boat on
this one. An ELECTROMECHANICAL horn is an enhanced buzzer
with a diaphragm added for greater sound output. This
is an exemplar horn used on MANY thousands of S.E. aircraft.
The warning tones for this style of horn cannot be electrically
'mixed' into the signals that drive your overhead speakers.
[img]cid:.0[/img]
I designed an electronic stall/gear warning tone
generator for the Bonanza/Baron lines at Beech about
1980 time frame. This was not electro-mechanical
and used a special speaker I had specified for
very poor response as an audio device but very
efficient and with an aluminum cone for environmental
robustness.
The tones from this device could have been integrated
into the ship's audio system . . . but it was never
requested . . . at least while I was at Electro-Mech.
Similarly, the warning tones that are applied to
your cabin speakers CAN be tapped, conditioned and
mixed into your PMA8000 audio system.
The installation manual wiring diagrams show "unswitched audio
inputs . . .
[img]cid:.1[/img]
. . . with references to notes 6, 10, 11 . . .
[img]cid:.2[/img]
From this data I deduce that input #1 is always ported
to both speakers (if connected) and headset audio
irrespective of condition for any system controls.
There MIGHT be a simpler way to do this but without
more cogent knowledge of how all the components
are built and wired, the most conservative approach
has a 99% probability of being good-out-of-the-box.
Consider this interface circuit for tapping your speaker
wiring and routing through isolation transformers
to eliminate all possibilities for ground loops and/or
unanticipated sneak paths. Two potentiometers will
allow you to adjust the volume of each tone independently
before they are mixed and applied to US-Input #1.
[img]cid:.3[/img]
You can try single-turn pots if you like but I think
the multi-turn, screwdriver adjust will provide a more
vernier command of the audio levels and will 'stay put'
with time.
Bob . . .
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