I got an old 80-0557-11 Rev A manufactured by Grimmes from an EMB-120 Brasilia, and I was wondering how to make it speak.

I powered the component with a 28VDC power supply. It only said "Aural unit Ok" while I was expecting a lot of warnings, due the lack of connected sensors.

Checking an old wiring manual, I realized that most of the sensor inputs have a single connection, not a "HI/LO (+/-)" lines.

Does someone have some idea about how make it play alarms?

Thank you in advance for anyone who can explain me the logic of the system. Please, keep in mind that I'm just a enthusiast trying to better understand how this system works.

  • $\begingroup$ I suspect that "Aural Unit OK" is just an internal self-test. In order for it to "speak what she knows", it may have to be hooked into real (or simulated) signals. Without having a wiring diagram or information on how this unit hooks up and communicates, it will be a very difficult question to answer. While not off-topic because it requires product-specific information, this knowledge is highly specialized and it may be unlikely to get an answer here. $\endgroup$
    – Ron Beyer
    May 8, 2017 at 19:29
  • $\begingroup$ @RonBeyer Thank You for your comment Ron, i understand that's highly speciacialized knowledge, but maybe it's not a mistery like we expect. That's the reason why i brought this question to this room! :) $\endgroup$
    – drmwndr
    May 8, 2017 at 19:38
  • $\begingroup$ Are you sure it should say something when powered on but without the various sensors? It may be working exactly as designed. Sounds like you've got (at least some of) the manuals, so that, mostly likely, makes you more expert on this than any of us. (Unless, of course, an A&P happens to wander by who knows this particular unit...) $\endgroup$
    – FreeMan
    May 8, 2017 at 20:07
  • $\begingroup$ This Ops Manual may be of help. The aural unit can pass-through audio from devices such as the TAWS or TCAS. Most of the other alerts are internally stored audio files that are triggered by the external systems. The single wire connections are discretes. They may be OPEN/GROUND (try grounding to see if it triggers) or 28V/OPEN (applying 28V will trigger). $\endgroup$
    – Gerry
    May 9, 2017 at 0:16
  • $\begingroup$ @Gerry The Ops Manual tip was great. I was analyzing just the aircraft maintenance manual. I'll try to grounding and if it doesn't work i'll look for more info if it's safe to apply 28V on this lines. Thank you Gerry! :) $\endgroup$
    – drmwndr
    May 9, 2017 at 12:23

1 Answer 1


Answering my own question based on tips posted on comments:

As @Gerry suggested on comments, they are OPEN/GROUND, if i ground any of sensor cables it'll trigger the alarms. Those lines are 5V, and i think that most of sensors are just simple switches, except for the Fire Alarms, that i couldn't trigger and has 6.8V over its line.

For now i got my AWU speaking.

Thank everybody who commented with their suggestions. Those were very very very useful, you guys are awesome!

  • $\begingroup$ The fire signals come from something called a 'fire loop', which is basically a wire-shaped thermistor wrapped around the engine/apu. Maybe researching that will lead you to a solution. Its amazing you didn't fry your box experimenting with it, good work! $\endgroup$
    – nexus_2006
    May 11, 2017 at 0:54

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .