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Is there a switch configuration that will do this?

 
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david(at)carter.net
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PostPosted: Thu Jun 17, 2021 8:29 am    Post subject: Is there a switch configuration that will do this? Reply with quote

I'd like to have a single switch control both my taxi lights & landing lights. Sounds simple enough, right? Here's the catch. I want to control the taxi lights directly from this switch by making a connection to +12v. The landing lights, however, will be controlled through the Garmin GAD 27 electrical controller "magic box" so that it can provide airspeed-based wig-wag. The GAD 27 light control switch input is active-low. 

How I'd like it to work:
1. Switch down - both lights off
2. Middle position - +12v supplied to the taxi lights. 
3. Top position - taxi lights no longer connected to +12v, GAD 27 light switch input connected to ground. 
I know I can do this with a relay, but I'd rather avoid adding an additional failure point. It's not the end of the world if I use separate switches for these functions, but I'd prefer they are combined on one switch. 
Thanks,
David
---
David Carter
david(at)carter.net (david(at)carter.net)


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david(at)carter.net
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PostPosted: Thu Jun 17, 2021 1:59 pm    Post subject: Is there a switch configuration that will do this? Reply with quote

Quote:
> There MIGHT be a simple way to do this but it
>>   depends on the 'pull down' current of the electrical

>>   controller. Is there a spec for that device that speaks
>>   to parameters of this input?

Here's what I was able to find in the installation manual: (top of page 26-8, or page 342 in Acrobat Reader)
https://static.garmin.com/pumac/190-01115-01_an.pdf
These active-low discrete inputs conform to the following specification:

Low: Vin < 3.5 VDC, or Rin < 375 Ω (input active)
High: Vin > 8 VDC, or Rin> 100k Ω (input inactive)

---
David Carter
david(at)carter.net (david(at)carter.net)

On Thu, Jun 17, 2021 at 5:37 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
At 11:28 AM 6/17/2021, you wrote:
Quote:
I'd like to have a single switch control both my taxi lights & landing lights. Sounds simple enough, right? Here's the catch. I want to control the taxi lights directly from this switch by making a connection to +12v. The landing lights, however, will be controlled through the Garmin GAD 27 electrical controller "magic box" so that it can provide airspeed-based wig-wag. The GAD 27 light control switch input is active-low.Â

How I'd like it to work:
1. Switch down - both lights off
2. Middle position -Â +12v supplied to the taxi lights.Â
3. Top position - taxi lights no longer connected to +12v, GAD 27 light switch input connected to ground.Â

I know I can do this with a relay, but I'd rather avoid adding an additional failure point. It's not the end of the world if I use separate switches for these functions, but I'd prefer they are combined on one switch.Â

  There MIGHT be a simple way to do this but it
  depends on the 'pull down' current of the electrical
  controller. Is there a spec for that device that speaks
  to parameters of this input?



  Bob . . .

  Un impeachable logic: George Carlin asked, "If black boxes
  survive crashes, why don't they make the whole airplane
  out of that stuff?"



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user9253



Joined: 28 Mar 2008
Posts: 1907
Location: Riley TWP Michigan

PostPosted: Fri Jun 18, 2021 8:53 am    Post subject: Re: Is there a switch configuration that will do this? Reply with quote

You need a DP3T ON-ON-ON switch.
Mouser and Digikey and others sell them.
https://www.mouser.com/Electromechanical/Switches/Toggle-Switches/_/N-5g2jZ1yzvvqx?P=1z0z2o3Z1z0z28f
https://www.digikey.com/en/products/filter/toggle-switches/201?s=N4IgjCBcpgzADFUBjKAzAhgGwM4FMAaEAeygG0RYAWeWAdgE4QBdIgBwBcoQBlDgJwCWAOwDmIAL5EATLACsSEKkiZchEuUoAOafABseluy6ReAkeKkgAtNMXKBAV3WlIFBcwlW7bkABEABVgAFRYJIA


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david(at)carter.net
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PostPosted: Mon Jun 21, 2021 10:49 am    Post subject: Is there a switch configuration that will do this? Reply with quote

Quote:
   P.S. those 'loose' components present a small
   packaging problem.  I think I'd fabricate an
   assembly-under-heat-shrink of the three compoents
   with wires coming out each end.
   Use 1/2" dual wall heat shrink . . . that's
   how I packaged a few hundred crowbar ov management
   modules.
   Your finished assembly will be about 1-1/2 inches
   long and 3/8" in diameter. It would tie nicely
   into an adjacent wire bundle. I've got all the
   materials in stock. I could build one up for you.


Bob - thanks for the solution design & for the packaging tip. I was also wondering how much heat the resistor would need to dissipate in this application? I'm guessing not much? 
---
David Carter
david(at)carter.net (david(at)carter.net)
On Mon, Jun 21, 2021 at 12:26 PM Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:

Quote:
Quote:
  This switch with addition of two
  diodes and the resistor cited above can be configured
  to accomplish the switching functions you requested.
  See attached:

   P.S. those 'loose' components present a small
   packaging problem.  I think I'd fabricate an
   assembly-under-heat-shrink of the three compoents
   with wires coming out each end.

   Use 1/2" dual wall heat shrink . . . that's
   how I packaged a few hundred crowbar ov management
   modules.

   Your finished assembly will be about 1-1/2 inches
   long and 3/8" in diameter. It would tie nicely
   into an adjacent wire bundle. I've got all the
   materials in stock. I could build one up for you.


  Bob . . .

  Un impeachable logic: George Carlin asked, "If black boxes
  survive crashes, why don't they make the whole airplane
  out of that stuff?"



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