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Wolfgang,
Unless you have access to a secret source of information not available to the rest of us, your comments are completely baseless. Have you actually looked at the schematic posted on BakerAircraft.com's website at http://www.barkeraircraft.com/files/AOA_rDisplay.pdf ? Have you actually understood it?
If you actually study the circuit on page 6, you will see that the LEDs are connected to the "+14V In" input voltage and they are set up to run at 24mA not the "typical 10mA" that you pulled out of thin air. At 13.8V input and a drop of 2.2V on the LEDs, the chip has to dissipate 11.6V at 24mA or 278mW. At a Theta-J-A of 55C/W, this leads to a 15C increase per LED that is actually on.
Next time please study the subject matter before posting.
Regards,
Hamid
Wolfgang wrote:
The home made AoA indicator from BarkerAircraft.com has a 5V regulator. With that running the electronics and a 2.2V typical forward V @ 10ma on the LED's, that leaves 2.8V at 100ma total dissipated by the chip with all LED's illuminated. The total dissipation of the chip comes out to about 0.28W. I don't see that raising the chip temperature to any where neat a 100C limit.
Wolfgang
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From: Hamid Wasti <hwasti@lm50.com>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] Do-it-yourself AOA Project
Date: Mon, 11 Jan 2010 19:41:18 -0500
To: lml@lancaironline.net
It is an interesting product with some clever ideas, but a very poor implementation. It is unlikely that it will keep working reliably for long in the real-world/real-aircraft environment.
The system does not take into account flap deployment. Anyone here use flaps?
The "normal" position of the probe is with the Hall sensor at the zero point of the magnet. Anyone concerned about the fact that the system could report "normal" output if the probe or the magnet falls off?
Even the most rudimentary analysis of the Hall sensor's output as its temperature varies from -20C to +50C would reveal a potential for some worrisome inaccuracies. You could stall several LEDs before you expect to, or you could be several LEDs away from a stall when the system says you should be stalling. Would you be more or less likely to actually stall in these situations?
The design does not take into account the fact that each LED that is on will cause the main IC's temperature to rise by about 15C. A little slow flight practice with a 6 LEDs on and the IC is well past its 100C limit, generating a burning smell and possibly smoke. Same would happen after an engine out as you glide down at best glide speed. Can you think of a worse time to find smoke in the cockpit?
This is just a partial list of issues, but I think it gets the picture across. The only thing worse than not having something is having something that is not reliable.
Regards,
Hamid
Gary Fitzgerald wrote:
/He has an article on this project in the Dec. 2008 edition of Sport
Aviation. Interesting use of a Hall Effect sensor./
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