737 Yoke Pitch Trim switches question?

[XOrionFE]

Are the two trim switches on the real yoke meant to have to be activated at the same time in one direct in order to activate the trim?   Or are they simply redundant to each other?

I am getting ready to wire mine and it basically has 5 wires going to it.   One is a common ground and the other 4 each go to one direction of each of the two switches.

So I am thinking I just wire Nose down wires from each of the two switches together and then hook to one input and wire the Nose up wires from the two together into a second input.    I plan on putting these onto a Bodnar board which will also be controling the pitch and roll pots.    The copilots side has the same switches so thinking these can be wired the same way and joined to the same 2 inputs as the pilot side.

I also have the mic and AP disconnect switches to wire which each will take up an input as well but again, i figure those two inputs can be wired also to copilots side buttons.

Does this all make sense?   Let me know if it sounds wrong or if I am wiring the trim switches incorrectly.

Thank you,
Scott

[Trevor Hale]

Hi Scott,

In the real aircraft there are 2 hydraulic systems that operate the elevator.  Both are redundant to each other.  Each switch is assigned to each system.  However if I am not mistaken, pressing one does nothing, and pressing the other does nothing, but both together shares the load on the trim system and allows the system to work.

Therefore for ultimate in realism, I would wire both switches in a series/parallel configuration, so that both have to be pushed in the same direction for them to work.

Trev

[Bob Reed]

Real simple answer. Trevor already answerd it..... Yup.....

[XOrionFE]

Hmmm

This is confusing.   I have two different yokes which are from different planes and they have different types of switches.    Maybe they are different though because of being captain versus First Office side.

The switches have wiring diagrams on them but I for the life of me cant figure out the best way to wire it.  I used the Red/Wht on the Cpt side as a common gnd and was able to test each switch position with a continuity tester and came up with the switch position for each which I wrote down.

On the F/O side though I havent a clue.   This probably works more like Trevor's idea.   Only on this one there are only 4 wires instead of 5.   

Can anyone help suggest how to wire these.   Making them work like Trevor said would be the way to go I think but I cant figure out how.   I have attached a diagram of each type.  If it doesnt show big enough on this site you can also go to this link. http://farm3.static.flickr.com/2766/4179139983_af4a70ace6_o.jpg

[Trevor Hale]

Hey Scott,  There are always more then one way to skin a cat.. (But we don;t condone that, cause I have 4 and I love them all) Regardless.

If you want to do this the "complicated" way, you will need to connect the switches to a relay, and using the relay you can create the 100% proper logic, to only allow the systems to work "IF" all the correct logics are met.  But most people don;t have relays's kicking around.

You can make it work if you follow this schematic.  If you want me to do one with the relay I can do that also.  but either way. 

Technically as long as both switches are moved.. this would be the easiest way to do this.  The one on the right could be either up or down.. which would be very awkward to do, but who would really try that in your setup.. LOL

anyway, here you go..  if you have any questions, please ask.

[XOrionFE]

This looks like it would work great but the problem is that these types of switches are wired like two seperate switches shown and the units are sealed with only the wires shown on the diagram coming out.   I think they are internally wired a certain way as the diagrams I sent show.   So there is not two seperate ground terminals for instance.

[Trevor Hale]

OK, sorry, I thought you had a wire for every terminal.

Then if that is the case and on the Pilot side wiring diagram, you would need a relay to connect to that, to make it work  the way you want it too.

Lat me see what I can figure out for that.  Assuming these wiring diagrams are all you have access to. I do have tonnes and tonnes of relays too, so if I needed to send you a couple, that wouldn't be an issue.

Trev

[XOrionFE]

Thanks Trevor

The bright side is that they are real :-).  Should be really nice if I can make them work real also.   Getting close now to having my columns all working.   I am for now going to run a couple Cat5e cables up the columns so I will have 16 leads on pilot side and 8 on copilots and can come back and wire switches later once figured this out.

I hope to take a little video of the setup before the weekend is over.

[Trevor Hale]

Woot,  sounds like a lot of fun..  Looking forward to some vid's  I will work on your issue right now.

[XOrionFE]

Hey thanks!

I dont want you to kill your Sat night though...I am sure you have things on your sim you need to get done also. 

[Trevor Hale]

OK, for the F/O Side.. it is very easy to wire..

Connect White/Red to Input card Common
Connect White/Orange to (Trim Up) Input
Connect White/Black/Orange to (Trim Down) Input.

White/Violet.. = NO CONNECTION

Easy no problem..


Here is the Captain Solution..

Trev

[Boeing Skunk Works]

I can give you the diagram from the Boeing manual that I used, but for the life of me I can't remember how I wired them. Mine both have to be pressed together to get the trim to work. One or the other will not do anything.

It was so long ago I don't remember how I did this and I can't see the wiring.

[Trevor Hale]

Hope the above helps Scott.  If you need the relays let me know, I will dig some out.

Trev

[XOrionFE]

Thanks guys!! 

I am trying to digest.

[XOrionFE]

Ok, just had to learn a little about relays.   This is pretty cool the way this works.  A little more than I bargained for but looks easy enough.   I dont have any relays but probably could pick some up cheap enough at Radio Shack if you could point out which type http://www.radioshack.com/search/index.jsp?kwCatId=&kw=relay&origkw=relay&sr=1

Thanks again Trevor...this will be awesome to have them operating correctly

Scott

[Trevor Hale]

                     Model: 275-249                     | Catalog #: 275-249

That one will do nicely, so you would need 4 of them.

Keep in mind, each actually has 2 sets of independent dry contacts, but you will only be using one set on each relay.

What I am actually doing with the relays is isolating the second switch. and the first switch only allows the second switch to operate if that makes sense.

Relays are awesome, They allow you to control High voltage things with low voltage switches.

For instance, these relays I selected for you can pass 5A at 250Volts..  so in essence is you had a 120V light bulb or Christmas light bulb string, or something, they could effectively be turned on and off through a small 12V Switch.

I use a relay to isolate my computer power supplies, and 120V air conditioning unit for the cockpit.

If you ever wanted to use (Real aircraft panels) with 28V lamps like in Mikes 727, you would need Relays to isololate the high voltage from the 12V supplied by your computer power supply etc.

Trev
         

[XOrionFE]

That is why I really love this hobby.  I learn so much from everyone and from doing the many different projects required to build a cockpit.    I have done woodworking, astronomy, RC planes, etc but none compare to the variety of skills necessary to build a pit.    And being able to learn various electronics things like this from folks like you is great.   I really appreciate the help and the lesson.   I see using more relays in the future possibly.    I do have 3 power supplies set asside and already converted for supplying my 12v and 5v power. 

I assume that using some normal low voltage category 5 cable should still be fine for this project between the switches and the relays correct?   I will use a little heavier from the relays (12V) to the power supply.

[Trevor Hale]

The cat5 cable should be fine for all of it. it is all low current stuff.

One thing you will see in most diagrams, they show a diode across the relay (coil) + and -  I would pick up 4 diodes to go with your relays, these prevent any feeback from the coil shooting back to your power supply.  Just remember to put the >| <-- black or white line of the diode towards the + side of the coil

No worries, we are all here to help you, and if you still have questions, you know where to find me.

Trev

[XOrionFE]

Great

Thanks again.    I will post the result.   I am sure this thread will be great for someone else too down the road.

[Garys]

Hi Guys, Dont mean to take anything away from this thread but I think the Trim switch is being made overly complicated. On the real aircraft one of the switches is used as an electrical ground to the actuator which of course makes the trim system electrically incomplete without both of those switches used together. It isnt for the independant use of hydraulic systems A or B which I think is a misunderstanding.

Using the diagram on the switch and a multimeter I was able to find the grounds and up/down of the switch pretty easily, but like Mike that was a long time ago. As long as you have those, the actual ground switch for the actuator can stay unwired, unless of course you would like to simulate trim system malfunctions as well.

[Trevor Hale]

Awesome...Appreciate that Gary..  My dual trim system for my old Falcon 900B was set up  dual hydraulic systems, I assumed the 737 would be similar. That was a misunderstanding regarding the behind the scenes operation,  however..  My circuit diagram for Scott will still work, as the left switch will allow the right one to operate as you stated.

[Garys]

Your welcome Trevor. Yep your diagram will still work for sure. With mine I just have the one switch wired up into the interface. The other side just goes along for the ride :-)

[Trevor Hale]

Ahhhh... That makes perfect sense..  Cheers,

Trev