# Encoding altimeter to transponder

Discussion in 'Instruments / Avionics / Electrical System' started by Offcenter, Jun 9, 2009.

1. Jun 9, 2009

### Offcenter

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Gentlemen, I have a Smiths Industries encoding altimeter, part # 01-200-103. And I have a ARC RT-859A transponder. I'd like to interface them in the Challenger I'm building. I've googled myself silly and can't find much of anything about how to hook them together. I've also checked the Essco site but they show nothing at all for Smiths instruments.
Furthermore, the altimeter has a 26 pin male fitting on the back for which I need the matching female plug to go on my wiring harness. Can't find anything on that either.
Does anyone have any idea at all where I should look or where I should start with this?
Anything would be appreciated at this point.

2. Jun 14, 2009

### wally

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Hi,
Our airplanes here at work use some Smiths instruments however I could find no information on the part number you have. Smiths is a UK company very big in Aerospace instruments and electronics. I have 52 CDs covering Smiths Component Maintence Manuals but nothing for your part.

I did find that in 2007 GE bought Smiths Aerospace. It is now called GE Aviation Systems.

The only info that might be of help is the Smiths Aerospace U.S.A. office address from a few years ago.

Smiths Aerospace
PO Box 9013
Clearwater FL 33758
phone 727-539-1631

What I hope you have is an encoding altimeter with a 7 wire gray code output that can be a direct input to the transponder.

There is no telling without a wiring print. It could also be a syncro output or data bus output of some sort or who knows! If it came from a jet, it probably also has a built in vibrator to jiggle the gears and help accuracy - not needed on piston plane installations. Some jets like Sabreliners did however have a separate panel vibratior. Some Sabreliners used Smiths "Look-Alike" instruments for the co-pilot that looked like the Rockwell Collins stuff on the left side but a bit less .

The ones I found info on are combination airspeed and altitude instruments used on MD-11 planes. It is used as a standby, or backup instrument for the rare times that one or more of the 6 glass panels have only a big red X on them!

They make a huge assortment of electronics.

Sorry I can't be more help.
Wally

3. Jun 14, 2009

### Offcenter

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Thank you, Wally. I'll have to try giving them a call when I get a chance. Since I posted that I did manage to find a 26 pin plug for the back of the altimeter. What I'm curious about is, if it is a 7 wire gray code, why use a connector with 26 pins?
Thanks again, Wally.

4. Jun 15, 2009

### wally

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That is really hard to figure. It is "possible" that they have standardized their design a bit. That way they can use a single container with one size connector cutout and mounting in the end. In that one container they could offer all sorts or gizmos like airspeed, altimeter, both together or maybe a standby gyro horizon, with various kinds of inputs: power, grounds, lighting, vibrator, and serial bus, syncro or other outputs. They use whatever pins they need and the rest are not connected.

Also that way, by switching the used pins around, if someone accidently plugs the wrong instrument in, If they wired it right, then even if the plugs mate, no power, ground, or signals get crossed and burn something up. The pins match up with unused pins on the other side since it is not the right part.
Just a guess.
Wally

5. Jun 16, 2009

### Offcenter

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Makes sense, Wally. By the way, on that altimeter, number #01-200-103, you said you could find no reference to it. I found a
date on the unit from when somebody serviced it....in 1979!!
It's been around a while. Seems to work fine mechanically.
I've taken it out
in the car up and down some of the steeper hills in the area and it
reacts smoothly and gives correct altitude for the hills I'm familiar
with. What's not known is if the encoder will send out the proper signals to the transponder.

6. Sep 6, 2009

### joesr

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:ermm:Hi all,Im new to this site.I just bought a eaa bi plane single seat very tight,i need a transponder and radio.can anybody suggest anything used i can look for.It had a radio and was removed but the connector is still intact

7. Sep 6, 2009

### wally

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Hi, I just did a little looking around the interwebs but didn't find much that would help you.

You will probably have to do some re-wiring no matter what you find.

What I have seen in some homebult planes is a handheld VHF comm with a headset adapter. It seems to work pretty well. You would not need to do much for that. Just attach the antenna cable and plug in a headset adapter. You can mount it with velcro or tie-wraps. You can buy a new one for only a couple hundred.

Do you really need a transponder? They are going to be kinda expensive.

If you do decide on new panel-mount, I would like to recommend the radio I bought and like. It is a Flightline, FL-760 comm. It is Japanese and looks similar to Becker and Microair. It is 2 and a 1/4 inches square and not very deep. It is available in various places for about $650 or so. It has a built-in 2 place audio control and some other nice features. The other radio I like (I have in my Cessna) is the Val-com 760. It is no longer sold new and the newer version is over$1000.

Icom makes a nice radio too.

Also ask around at your local airport and see if someone might know who to talk to or where to look.
Best wishes,
Wally