X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 13 Jan 2010 16:08:12 -0500 Message-ID: X-Original-Return-Path: Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125] verified) by logan.com (CommuniGate Pro SMTP 5.3.1) with ESMTP id 4081508 for lml@lancaironline.net; Wed, 13 Jan 2010 14:51:19 -0500 Received-SPF: none receiver=logan.com; client-ip=71.74.56.125; envelope-from=Wolfgang@MiCom.net X-Original-Return-Path: X-Authority-Analysis: v=1.0 c=1 a=50vDblQ1AAAA:8 a=dOoDZmAWAAAA:8 a=Ia-xEzejAAAA:8 a=pdDl4ngrAAAA:8 a=qfM1wD_kpyxmox1EoesA:9 a=RiNz_xN6xcoU2dsP7xeMCPMgcPUA:4 a=EZD7PgxjWdgA:10 a=XY96fHeFyScA:10 a=f-MNE9I93sYA:10 a=EzXvWhQp4_cA:10 a=V_cC3ne3A8d2iGCg8a8A:9 a=yiNLqCpSlfqrvXwCN0sA:7 a=MeDol737caXE_ssf3SALgxZ8kRgA:4 X-Cloudmark-Score: 0 X-Originating-IP: 74.218.201.50 Received: from [74.218.201.50] ([74.218.201.50:1942] helo=micomxp) by hrndva-oedge02.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 2D/02-17464-4142E4B4; Wed, 13 Jan 2010 19:50:44 +0000 X-Original-Message-ID: <000d01ca9489$ae62c760$6401a8c0@micomxp> From: "Wolfgang" X-Original-To: Subject: Re: Do-it-yourself AOA Project X-Original-Date: Wed, 13 Jan 2010 14:50:38 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000A_01CA945F.C509ACB0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_000A_01CA945F.C509ACB0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I had not looked at the schematics, just the parts list. The LED's are, = in fact going back to 12V/14V. http://www.barkeraircraft.com/files/AOA_rDisplay.pdf Agreed, this is not a good idea but starting a fire is not an expected = result either. At least 40 years in electronics shows me that. Based on the LM3914 spec sheet, the LED current comes out to 23ma. 520 = ohms in parallel with 10K on 1.25V. Paralax error maybe? With a 100C limit,an ambient of 40C and 55C/W, the allowable disipation = is 1.09W. With all LED's on at 230ma, that allows 7V on the LED's. A simple solution would be to have the 5V regulator with a heat sink = feed the LED's. . . . . what I assumed in the first place. I like offering a fix rather than just crtiticism. Wolfgang -------------------------------------------------------------------------= ------- From: Hamid Wasti =20 Sender: =20 Subject: Re: [LML] Re: Do-it-yourself AOA Project=20 Date: Wed, 13 Jan 2010 11:07:58 -0500=20 To: lml@lancaironline.net=20 =20 =20 =20 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. =20 Wolfgang = ------------------------------------------------------------------------ From: Hamid Wasti Sender: Subject: Re: [LML] Do-it-yourself AOA Project Date: Mon, 11 Jan 2010 19:41:18 -0500 To: lml@lancaironline.net =20 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 =20 ------=_NextPart_000_000A_01CA945F.C509ACB0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
I had not looked at the schematics, = just the parts=20 list. The LED's are, in fact going back to 12V/14V.
http://www.= barkeraircraft.com/files/AOA_rDisplay.pdf
Agreed, this is not a good idea but = starting a fire=20 is not an expected result either. At least 40 years in electronics shows = me=20 that.
 
Based on the LM3914 spec sheet, the LED = current=20 comes out to 23ma. 520 ohms in parallel with 10K on 1.25V. Paralax error = maybe?
With a 100C limit,an ambient of 40C and = 55C/W, the=20 allowable disipation is 1.09W. With all LED's on at 230ma, that allows = 7V on the=20 LED's.
 
A simple solution would be to have = the 5V=20 regulator with a heat sink feed the LED's. . . . . what I = assumed in=20 the first place.
 
I like offering a fix rather than just=20 crtiticism.
 
Wolfgang
lml@lancaironline.net
From: Hamid Wasti=20 <hwasti@lm50.com>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] Re: Do-it-yourself = AOA=20 Project
Date: Wed, 13 Jan 2010 11:07:58 = -0500
To:


 
Wolfgang,

Unless you have access = to a=20 secret source of information not available to the rest of us, your = comments are completely baseless. Have you actually looked at the=20 schematic posted on BakerAircraft.com's website at http://www.barkeraircraft.com/files/AOA_rDisplay.pdf = ?=20 Have you actually understood it?

If you actually study the = circuit=20 on page 6, you will see that the LEDs are connected to the "+14V = In" input=20 voltage and they are set up to run at 24mA not the "typical 10mA" = that you=20 pulled out of thin air. At 13.8V input and a drop of 2.2V on the = LEDs, the=20 chip has to dissipate 11.6V at 24mA or 278mW. At a Theta-J-A of = 55C/W,=20 this leads to a 15C increase per LED that is actually = on.

Next time=20 please study the subject matter before=20 posting.

Regards,

Hamid

Wolfgang wrote:
The home made AoA indicator from BarkerAircraft.com = has a=20 5V regulator. With that running the electronics and a 2.2V = typical=20 forward V @ 10ma on the LED's, that leaves 2.8V at 100ma total=20 dissipated by the chip with all LED's illuminated. The total = dissipation=20 of the chip comes out to about 0.28W. I don't see that raising = the chip=20 temperature to any where neat a 100C=20 = limit.
 
Wolfgang
-----------------------------------------= -------------------------------
From:=20 Hamid Wasti <hwasti@lm50.com>
Sender:=20 <marv@lancaironline.net>
Subject: Re: [LML] = Do-it-yourself AOA=20 Project
Date: Mon, 11 Jan 2010 19:41:18 -0500
To:=20 lml@lancaironline.net



 

It is an = interesting=20 product with some clever ideas, but a very poor implementation. = It is=20 unlikely that it will keep working reliably for long in the=20 real-world/real-aircraft environment.

The system does not = take=20 into account flap deployment. Anyone here use flaps?

The = "normal"=20 position of the probe is with the Hall sensor at the zero point = of the=20 magnet. Anyone concerned about the fact that the system could = report=20 "normal" output if the probe or the magnet falls = off?

Even the=20 most rudimentary analysis of the Hall sensor's output as its = temperature=20 varies from -20C to +50C would reveal a potential for some = worrisome=20 inaccuracies. You could stall several LEDs before you expect to, = or you=20 could be several LEDs away from a stall when the system says you = should=20 be stalling. Would you be more or less likely to actually stall = in these=20 situations?

The design does not take into account the = fact that=20 each LED that is on will cause the main IC's temperature to rise = by=20 about 15C. A little slow flight practice with a 6 LEDs on and = the IC is=20 well past its 100C limit, generating a burning smell and = possibly smoke.=20 Same would happen after an engine out as you glide down at best = glide=20 speed. Can you think of a worse time to find smoke in the=20 cockpit?

This is just a partial list of issues, but I = think it=20 gets the picture across. The only thing worse than not having = something=20 is having something that is not=20 = reliable.

Regards,

Hamid
 ------=_NextPart_000_000A_01CA945F.C509ACB0--