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Post by daveinfl » Mon Jul 09, 2007 7:52 pm

I need a simple circuit to sound an audible allert "Check Gear" into an intercom system for an airplane (Experimental). The circuit would be acitivated by a simple 12V relay, feeding off a simple warning light circuit already installed in the aircraft. I can tap off the 12V cirucuit and utilize a simple IC for a 5V power supply.

I'm an engineer, but not electronic type. I have tinkered with Digital circuits a little though.

Can anyone point me to a simple circuit to do this? Maybe a STAMP circuit, etc.?

Any help would be appreciated.


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Chris Smith
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Post by Chris Smith » Mon Jul 09, 2007 8:30 pm

Perhaps the signal can send you a simple buzzer noise, IF it dosent park?

During the swing, nothing other than a "buzz" noise occurs, when it lands or parks, .....the noise goes away? 555

If its a falure,[ doesnt land or park] the noise doesnt quit.

[Right after the start down...wheel is safe,... or not? ]

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Post by shillyard » Mon Jul 09, 2007 9:33 pm

You may be able to use one of those small digital voice recorders that hook to a key chain.
If its not worth repairing its not worth buying.

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Post by Externet » Mon Jul 09, 2007 9:55 pm

Hello Dave.
The design of such circuit is not a simple matter, nor one to think of a 'simple' ic implementation; lives depend on its reliability.

Various redundant sensors in many places including motor motion, current draw, voltage supply, position, locking, unlocking, 'untripability' to collapse when on ground even when then commanded to retract, sets and reset status to not cause 'retracted' signal when on flight, overrides, image or light pipe to visual confirmation... and much more am sure am not considering.

Many people would implement a microcontroller, some would not rely on a crystal controlled processor nor any failure-prone electronics.
The liability of posting such circuit on a forum is to consider, and military specs components should be norm.

A buzzer is a buzzer, of simple availability and connection. A well thought logic circuitry is not.

I would go for a commercial proven system for peace of mind.

- Abolish the deciBel ! -

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Post by haklesup » Mon Jul 09, 2007 10:48 pm

I can think of a bunch of ways to do this. One could use a traditional digital voice recorder chip, and simply wire the relay to the enable pin (or whatever the chip requires to start playback. ... 1607-2.htm
(Holtek has a great product line for hackers)

While searching on DIgital voice chip, I found this

If you wanted to go the PIC route, the relay would input to the uController or PIC which would output ASCII text serially to this module which would make the announcement. Other warning indicators could be included wth this design.

Mixing the voice chip output with your intercom is easy. If there is not already another input jack, you probably only need a series cap between the chip output and the intercom line level input. A series pot to adjust level may also be necessary.

Electrically speaking you don't really need a relay but for isolation purposes, it won't hurt. If your curcuit fails, it should not compromise the indicator lamp or any other system. An Opto-Isolator will achieve this task just as well with less of a load on the indicator lamp power and no concern about magnetic or electrical noise near the instrumentation.

I'm assuming this is piggyback on any FAA approved warning systems already in place.

Other ideas I had involved hacking a MP3 USB stick player and its control buttons. Also search on "Voice Module", that had lots of good hits

If you pick a voice chip, I can comment more on implementation.

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