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Mark Phillips in TN
Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN
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 Posted: Thu Jun 07, 2007 8:11 pm Post subject: Annunciator HELP! |
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This post is for the techno-weenies- all others delete NOW!
Goal: Illuminate an annunciator light when TruTrak servos are OFF using NKK LB series illuminated pushbutton:
http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO
This device is a DPDT PB with LED lamp, built-in resistor for the LED. (Reason for using PB instead of simple lamp is provide built-in PTT function with N.O. contacts. LED has its own +&- contacts on back of switch)
Consultation with TruTrak reveals that the torque line (pin6) to either servo can be used to sense when power is applied to the servo, thereby providing the necessary input. They sent a drawing showing a 10K resistor tied to this pin gating on a darlington transistor to provide the switch (ground path) for a lamp. Good, but I need the light OFF when power is on this pin. Please don't ask why, this is what I want to happen.
I begged the list for guidance some time ago and Bob very generously supplied sketches (THANKS!) for how to achieve this using a IRF510 MOSFET to either (1) turn the lamp ON as TruTrak indicated, or (2) turn the lamp OFF by connecting the MOSFET between a 470 ohm resistor supplying the LED and ground, which I understand would essentially remove voltage from the LED by shorting its supply voltage to ground. With 13 volts supplied, this would be about 30mA through the MOSFET when it is gated on, probably not resulting in a new-clee-ur event. Problem is, I assume Bob is referring to the resistor normally used to control LED current and since in the LB series switches this resistor is built into the LED, connecting the MOSFET to the LED supply voltage would essentially result in a dead short (minus MOSFET internal resistance) to ground. I'd surmise Mr. MOSFET would melt?
Unless there is a more elegant solution, I suppose I could use the MOSFET to ground a relay coil and use NC contacts to operate the LED, which in my electronically-challenged understanding of this would get the job done. But even after hours of googling to understand these MOSFET monsters these questions remain:
What are the connections to this beast? "Gate" I understand- signal from servo to gate on MOSFET. But what the heck are the "Source" (pin opposite gate) and "Drain" (center pin)? I'm supposing "source" in this case would be connection to the relay coil and "drain" is ground. Correct? One place I looked (WebEE?) indicates the mounting flange for the MOSFET (TO-220 pkg) is common to "drain" so that makes sense if the thing is mounted to the airframe. But another source said to insulate this from ground. (?) Another speaks of monster heatsinks, but I seriously doubt the coil current (75mA) of the relay of choice (Omron LY2F) would make the MOSFET break a sweat...
If you managed to hang on this far, I'd sure appreciate some guidance- and if y'all got a better mousetrap, I'm willing to stick my neck out!
Thanks and let's spare the archives with a do not archive thingie-
Mark (I grok batteries....maybe) Phillips
See what's free at AOL.com.
[quote][b]
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nuckollsr(at)cox.net
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| Posted: Fri Jun 08, 2007 6:41 am Post subject: Annunciator HELP! |
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|
At 12:10 AM 6/8/2007 -0400, you wrote:
| Quote: | This post is for the techno-weenies- all others delete NOW!
Goal: Illuminate an annunciator light when TruTrak servos are OFF using
NKK LB series illuminated pushbutton:
<http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO>http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO
This device is a DPDT PB with LED lamp, built-in resistor for the
LED. (Reason for using PB instead of simple lamp is provide built-in PTT
function with N.O. contacts. LED has its own +&- contacts on back of switch)
Consultation with TruTrak reveals that the torque line (pin6) to either
servo can be used to sense when power is applied to the servo, thereby
providing the necessary input. They sent a drawing showing a 10K resistor
tied to this pin gating on a darlington transistor to provide the switch
(ground path) for a lamp. Good, but I need the light OFF when power is on
this pin. Please don't ask why, this is what I want to happen.
I begged the list for guidance some time ago and Bob very generously
supplied sketches (THANKS!) for how to achieve this using a IRF510 MOSFET
to either (1) turn the lamp ON as TruTrak indicated, or (2) turn the lamp
OFF by connecting the MOSFET between a 470 ohm resistor supplying the LED
and ground, which I understand would essentially remove voltage from the
LED by shorting its supply voltage to ground. With 13 volts supplied,
this would be about 30mA through the MOSFET when it is gated on, probably
not resulting in a new-clee-ur event. Problem is, I assume Bob is
referring to the resistor normally used to control LED current and since
in the LB series switches this resistor is built into the LED, connecting
the MOSFET to the LED supply voltage would essentially result in a dead
short (minus MOSFET internal resistance) to ground. I'd surmise Mr.
MOSFET would melt?
|
See if this helps:
http://www.aeroelectric.com/Pictures/Schematics/FiveOnOnePW.jpg
Bob . . .
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nuckollsr(at)cox.net
Guest
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| Posted: Fri Jun 08, 2007 6:49 am Post subject: Annunciator HELP! |
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|
At 12:10 AM 6/8/2007 -0400, you wrote:
| Quote: | This post is for the techno-weenies- all others delete NOW!
Goal: Illuminate an annunciator light when TruTrak servos are OFF using
NKK LB series illuminated pushbutton:
<http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO>http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO
This device is a DPDT PB with LED lamp, built-in resistor for the
LED. (Reason for using PB instead of simple lamp is provide built-in PTT
function with N.O. contacts. LED has its own +&- contacts on back of switch)
Consultation with TruTrak reveals that the torque line (pin6) to either
servo can be used to sense when power is applied to the servo, thereby
providing the necessary input. They sent a drawing showing a 10K resistor
tied to this pin gating on a darlington transistor to provide the switch
(ground path) for a lamp. Good, but I need the light OFF when power is on
this pin. Please don't ask why, this is what I want to happen.
I begged the list for guidance some time ago and Bob very generously
supplied sketches (THANKS!) for how to achieve this using a IRF510 MOSFET
to either (1) turn the lamp ON as TruTrak indicated, or (2) turn the lamp
OFF by connecting the MOSFET between a 470 ohm resistor supplying the LED
and ground, which I understand would essentially remove voltage from the
LED by shorting its supply voltage to ground. With 13 volts supplied,
this would be about 30mA through the MOSFET when it is gated on, probably
not resulting in a new-clee-ur event. Problem is, I assume Bob is
referring to the resistor normally used to control LED current and since
in the LB series switches this resistor is built into the LED, connecting
the MOSFET to the LED supply voltage would essentially result in a dead
short (minus MOSFET internal resistance) to ground. I'd surmise Mr.
MOSFET would melt?
|
See if this helps:
http://www.aeroelectric.com/Pictures/Schematics/FiveOnOnePW.jpg
Try the same technique as suggested before except the external
resistor needs to be fairly low resistance and handle a bit of
power . . . like just under 1 watt. The added resistance will
make the internal LED a tad dimmer but I suspect not so much that
it would be unsatisfactory. This is simpler than a relay and
easier to fabricate. You can put all the stuff on a "perf board"
from Radio Shack. They probably have all the parts too.
Bob . . .
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retasker(at)optonline.net
Guest
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| Posted: Fri Jun 08, 2007 8:54 am Post subject: Annunciator HELP! |
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No offense to Bob or his design, but using a 1W resistor to dissipate 1W
is not a recipe for a long and reliable life for the resistor. When we
design electronics circuits we always de-rate components significantly,
which Bob also normally does.
I would suggest the attached circuit (I hope it attaches), all
components of which are readily available at Radio Shack or a number of
other component houses. While it uses a couple additional parts, they
are cheap and easy to use. This circuit will do what you want and not
dissipate much of anything in either state.
Respectfully,
Dick Tasker
Robert L. Nuckolls, III wrote:
| Quote: |
<nuckollsr(at)cox.net>
At 12:10 AM 6/8/2007 -0400, you wrote:
> This post is for the techno-weenies- all others delete NOW!
>
> Goal: Illuminate an annunciator light when TruTrak servos are OFF
> using NKK LB series illuminated pushbutton:
>
> <http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO>http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO
> This device is a DPDT PB with LED lamp, built-in resistor for the
> LED. (Reason for using PB instead of simple lamp is provide built-in
> PTT function with N.O. contacts. LED has its own +&- contacts on
> back of switch)
>
> Consultation with TruTrak reveals that the torque line (pin6) to
> either servo can be used to sense when power is applied to the servo,
> thereby providing the necessary input. They sent a drawing showing a
> 10K resistor tied to this pin gating on a darlington transistor to
> provide the switch (ground path) for a lamp. Good, but I need the
> light OFF when power is on this pin. Please don't ask why, this is
> what I want to happen.
>
> I begged the list for guidance some time ago and Bob very generously
> supplied sketches (THANKS!) for how to achieve this using a IRF510
> MOSFET to either (1) turn the lamp ON as TruTrak indicated, or (2)
> turn the lamp OFF by connecting the MOSFET between a 470 ohm resistor
> supplying the LED and ground, which I understand would essentially
> remove voltage from the LED by shorting its supply voltage to
> ground. With 13 volts supplied, this would be about 30mA through the
> MOSFET when it is gated on, probably not resulting in a new-clee-ur
> event. Problem is, I assume Bob is referring to the resistor
> normally used to control LED current and since in the LB series
> switches this resistor is built into the LED, connecting the MOSFET
> to the LED supply voltage would essentially result in a dead short
> (minus MOSFET internal resistance) to ground. I'd surmise Mr. MOSFET
> would melt?
See if this helps:
http://www.aeroelectric.com/Pictures/Schematics/FiveOnOnePW.jpg
Try the same technique as suggested before except the external
resistor needs to be fairly low resistance and handle a bit of
power . . . like just under 1 watt. The added resistance will
make the internal LED a tad dimmer but I suspect not so much that
it would be unsatisfactory. This is simpler than a relay and
easier to fabricate. You can put all the stuff on a "perf board"
from Radio Shack. They probably have all the parts too.
Bob . . .
|
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john(at)ballofshame.com
Guest
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| Posted: Fri Jun 08, 2007 9:07 am Post subject: Annunciator HELP! |
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Why not use 2 transistors to invert the signal instead?
-John
www.ballofshame.com
| Quote: |
<nuckollsr(at)cox.net>
At 12:10 AM 6/8/2007 -0400, you wrote:
>This post is for the techno-weenies- all others delete NOW!
>
>Goal: Illuminate an annunciator light when TruTrak servos are OFF using
>NKK LB series illuminated pushbutton:
>
><http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO>http://rocky.digikey.com/scripts/ProductInfo.dll?Site=US&V=360&M=LB25RKW01-5C-JC-RO
>
>This device is a DPDT PB with LED lamp, built-in resistor for the
>LED. (Reason for using PB instead of simple lamp is provide built-in PTT
>function with N.O. contacts. LED has its own +&- contacts on back of
> switch)
>
>Consultation with TruTrak reveals that the torque line (pin6) to either
>servo can be used to sense when power is applied to the servo, thereby
>providing the necessary input. They sent a drawing showing a 10K
> resistor
>tied to this pin gating on a darlington transistor to provide the switch
>(ground path) for a lamp. Good, but I need the light OFF when power is
> on
>this pin. Please don't ask why, this is what I want to happen.
>
>I begged the list for guidance some time ago and Bob very generously
>supplied sketches (THANKS!) for how to achieve this using a IRF510 MOSFET
>to either (1) turn the lamp ON as TruTrak indicated, or (2) turn the lamp
>OFF by connecting the MOSFET between a 470 ohm resistor supplying the LED
>and ground, which I understand would essentially remove voltage from the
>LED by shorting its supply voltage to ground. With 13 volts supplied,
>this would be about 30mA through the MOSFET when it is gated on, probably
>not resulting in a new-clee-ur event. Problem is, I assume Bob is
>referring to the resistor normally used to control LED current and since
>in the LB series switches this resistor is built into the LED, connecting
>the MOSFET to the LED supply voltage would essentially result in a dead
>short (minus MOSFET internal resistance) to ground. I'd surmise Mr.
>MOSFET would melt?
See if this helps:
http://www.aeroelectric.com/Pictures/Schematics/FiveOnOnePW.jpg
Try the same technique as suggested before except the external
resistor needs to be fairly low resistance and handle a bit of
power . . . like just under 1 watt. The added resistance will
make the internal LED a tad dimmer but I suspect not so much that
it would be unsatisfactory. This is simpler than a relay and
easier to fabricate. You can put all the stuff on a "perf board"
from Radio Shack. They probably have all the parts too.
Bob . . .
|
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rjquillin
Joined: 13 May 2007
Posts: 123
Location: KSEE
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| Posted: Fri Jun 08, 2007 10:28 am Post subject: Annunciator HELP! |
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At 09:51 6/8/2007, you wrote:
| Quote: | No offense to Bob or his design, but using a 1W resistor to
dissipate 1W is not a recipe for a long and reliable life for the
resistor. When we design electronics circuits we always de-rate
components significantly, which Bob also normally does.
|
Here's a link to an Ohmite pdf used for selecting and derating resistors.
http://ohmite.com/cgi-bin/showpage.cgi?product=appnotes_res_select.pdf&kw=resistor_selection__pdf_version_only_
The chart suggests no altitude derating below 5000 ft, increasing to
~.84 at FL250.
Other derating factors and a good old-fashioned nomograph is even included.
That one watt device really won't be happy with ~14 volts across it.
Ron Q.
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nuckollsr(at)cox.net
Guest
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| Posted: Fri Jun 08, 2007 11:12 am Post subject: Annunciator HELP! |
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At 12:51 PM 6/8/2007 -0400, you wrote:
| Quote: | No offense to Bob or his design, but using a 1W resistor to dissipate 1W
is not a recipe for a long and reliable life for the resistor. When we
design electronics circuits we always de-rate components significantly,
which Bob also normally does.
I would suggest the attached circuit (I hope it attaches), all components
of which are readily available at Radio Shack or a number of other
component houses. While it uses a couple additional parts, they are cheap
and easy to use. This circuit will do what you want and not dissipate
much of anything in either state.
Respectfully,
Dick Tasker
|
That works too. The 220 ohm was running a bit warm. 270 would be better.
Bob . . .
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Mark Phillips in TN
Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN
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| Posted: Fri Jun 08, 2007 11:40 am Post subject: Annunciator HELP! |
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In a message dated 6/8/2007 9:44:21 AM Central Daylight Time, nuckollsr(at)cox.net writes:
>>>
Helps?! Now I have no excuse to not get this puppy done- Bless yore punkin' heart, Bob- once again the muddy waters become crystaline!
VERY much appreciate the assist!
Mark do not archive
See what's free at AOL.com.
[quote][b]
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_________________
From The PossumWorks... |
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Mark Phillips in TN
Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN
|
| Posted: Fri Jun 08, 2007 12:04 pm Post subject: Annunciator HELP! |
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In a message dated 6/8/2007 9:52:21 AM Central Daylight Time, nuckollsr(at)cox.net writes:
| Quote: | The added resistance will
make the internal LED a tad dimmer |
Probably not a problem, but if necessary NKK offers internal LEDs w/o the resistor, but was hoping to keep all annunciator PBs the same.
Power to these lamps is via a PWM dimmer...
http://fdatasystems.com/LC_40.htm
...which they claim is "low frequency" without giving actual freq. My reading indicates MOSFETs operate well even at high freqs, so I suspect not a problem. Would this affect operation in any way i.e. extra heat?
With MOSFET on and dimmer at full power, current should be about 64 mA or about .9watts (if my bad math is close)- should I heatsink this thing or can I just screw it to a support rib behind the panel (with a dab of h/s compound) with short wires (pigtail) soldered to legs, covered in heatshrink to insulate them?
Thanks again!
Mark
See what's free at AOL.com.
[quote][b]
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Mark Phillips in TN
Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN
|
| Posted: Fri Jun 08, 2007 12:17 pm Post subject: Annunciator HELP! |
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In a message dated 6/8/2007 12:10:40 PM Central Daylight Time, john(at)ballofshame.com writes:
| Quote: | | Why not use 2 transistors to invert the signal instead? |
Hi John- As you likely noticed I can't even get my mind around ONE of the stupid things- could you elaborate? Better yet, send me a schematic, part#s etc. - I'm in full learn mode...
Appreciate the interest-
Mark do not archive
See what's free at AOL.com.
[quote][b]
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retasker(at)optonline.net
Guest
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| Posted: Fri Jun 08, 2007 12:38 pm Post subject: Annunciator HELP! |
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It runs at approximately 170-180 Hz.
Dick Tasker
Fiveonepw(at)aol.com wrote:
| Quote: | In a message dated 6/8/2007 9:52:21 AM Central Daylight Time,
nuckollsr(at)cox.net writes:
The added resistance will
make the internal LED a tad dimmer
Probably not a problem, but if necessary NKK offers internal LEDs w/o
the resistor, but was hoping to keep all annunciator PBs the same.
Power to these lamps is via a PWM dimmer...
http://fdatasystems.com/LC_40.htm
...which they claim is "low frequency" without giving actual freq. My
reading indicates MOSFETs operate well even at high freqs, so I
suspect not a problem. Would this affect operation in any way i.e.
extra heat?
With MOSFET on and dimmer at full power, current should be about 64 mA
or about .9watts (if my bad math is close)- should I heatsink this
thing or can I just screw it to a support rib behind the panel (with a
dab of h/s compound) with short wires (pigtail) soldered to legs,
covered in heatshrink to insulate them?
Thanks again!
Mark
------------------------------------------------------------------------
See what's free at AOL.com
<http://www.aol.com?ncid=AOLAOF00020000000503>.
*
*
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john(at)ballofshame.com
Guest
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| Posted: Fri Jun 08, 2007 1:03 pm Post subject: Annunciator HELP! |
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Actually, there was an e-mail that went out around the same time as mine
that actually had a schematic for such thing. I don't have all my e-mail
in front of me so I can't point you to it unfortunately but now that I
mentioned it you probably know exactly what I'm talking about (my
apologies for not being able to credit whoever drew the schematic).
The schematic showed regular transitors, I think. Bob had suggested a
FET, albeit in a slightly different application. I don't know enough
about the problem to really have an educated opinion on which is "better".
Maybe those two can duke it out and converge to the optimal solution.
-John
www.ballofshame.com
| Quote: |
In a message dated 6/8/2007 12:10:40 PM Central Daylight Time,
john(at)ballofshame.com writes:
Why not use 2 transistors to invert the signal instead?
Hi John- As you likely noticed I can't even get my mind around ONE of the
stupid things- could you elaborate? Better yet, send me a schematic,
part#s etc.
- I'm in full learn mode...
Appreciate the interest-
Mark do not archive
************************************** See what's free at
http://www.aol.com.
|
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kuffel(at)cyberport.net
Guest
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| Posted: Fri Jun 08, 2007 1:50 pm Post subject: Annunciator HELP! |
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|
Also <<No offense to Bob or his design>> or the several components of
Dick Tasker < can't even get my mind around ONE of the stupid things-
could you elaborate? Better yet, send me a schematic, part#s etc>> but
wouldn't the following work?
Change Bob's 220 (or 270) ohm resistor to 5k or maybe even 10k. Insert
one identical FET between the resistor and the switch. The junction of
the 1st Drain and the replaced resistor goes to the gate of the 2nd
FET. The drain of the 2nd FET is connected to lamp power (as is the
high end of the replaced resistor), the source goes to the high input of
the switch LED. The other end of the switch LED goes to ground as in
the original circuit.
So when the TruTrak pin 6 is high the 1st FET conducts. The current
through the new resistor lowers the voltage to the 2nd FET's gate and
turns it off, turning off the lamp. When the pin 6 is low the 1st FET
is off. Lamp power high goes through the 5k resistor to the 2nd FET
gate and turns it on, turning on the switch LED. This eliminates the
dimming of the lamp by running its power through a high wattage resistor.
Don't have the facilities to draw and attach a schematic but the change
to Bob's drawing is hopefully simple enough to be clear.
Tom Kuffel
AL7AU
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retasker(at)optonline.net
Guest
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| Posted: Fri Jun 08, 2007 3:19 pm Post subject: Annunciator HELP! |
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Kinda like this if you like FETs better... Both schematics attached.
Dick Tasker
The Kuffels wrote:
| Quote: |
<kuffel(at)cyberport.net>
Also <<No offense to Bob or his design>> or the several components of
Dick Tasker < can't even get my mind around ONE of the stupid things-
could you elaborate? Better yet, send me a schematic, part#s etc>>
but wouldn't the following work?
Change Bob's 220 (or 270) ohm resistor to 5k or maybe even 10k.
Insert one identical FET between the resistor and the switch. The
junction of the 1st Drain and the replaced resistor goes to the gate
of the 2nd FET. The drain of the 2nd FET is connected to lamp power
(as is the high end of the replaced resistor), the source goes to the
high input of the switch LED. The other end of the switch LED goes to
ground as in the original circuit.
So when the TruTrak pin 6 is high the 1st FET conducts. The current
through the new resistor lowers the voltage to the 2nd FET's gate and
turns it off, turning off the lamp. When the pin 6 is low the 1st FET
is off. Lamp power high goes through the 5k resistor to the 2nd FET
gate and turns it on, turning on the switch LED. This eliminates the
dimming of the lamp by running its power through a high wattage resistor.
Don't have the facilities to draw and attach a schematic but the
change to Bob's drawing is hopefully simple enough to be clear.
Tom Kuffel
AL7AU
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Mark Phillips in TN
Joined: 10 Jan 2006
Posts: 431
Location: Columbia, TN
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| Posted: Fri Jun 08, 2007 5:10 pm Post subject: Annunciator HELP! |
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In a message dated 6/8/2007 4:07:04 PM Central Daylight Time, john(at)ballofshame.com writes:
| Quote: | Actually, there was an e-mail that went out around the same time as mine
that actually had a schematic for such thing. |
>>>
Yeah, it was that Dick Tasker guy- if I understand it correctly, looks like a neat arrangement...
Thanks for the interest!
Mark do not archive
See what's free at AOL.com.
[quote][b]
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