Altimeter

[FFMan]

Has anyone tried making an altimeter. I see Motorola have a suitable sensor, but it seems there must be a number of issues to get round, like non linear changes with height, calibration and then changes occuring due to turbulence etc.

I know there are one or two commercial systems out there - has anybody tried one ?

[Gary Warner]

I haven't tried the commercially available units but I've seem then in use. The one's I've seen are very nice and accurate.

What's your application? Do you need accurate readings measured in absolute height or is it just relative height?

I've made one but I didn't want to know absolute height, just relative. I was for making a vertical speed sensor with a down-link. It was fairly easy (though not for a PIC beginner) to make with a Motorola sensor, gain and offset circuit and a PIC.

Gary
--

[FFMan]

I was looking for something that might give me some information about when my glider encounters true lift - i find it hard to see this accurately from the ground, partly through inexperience and partly cos often its too far away to see subtle changes.

I was thinking if i had an alitimter (calibration not necessary as i'm not really interested in figures) then I could down link either an audio tone or data and use the info to improve my flight times.

I'm handy with Basic stamps so developing code and interfaces isn't an issue, but I'd be interested in how anyone else might have done this.

Do you get duff readings due to air turbulence, and can you tell lift from height gain due to 'flying' or do you just use your brain to interpret the results ?

thanks from the UK

[Gary Warner]

Mine had a resolution of 1 meter - poor by todays standards. Mine was in a sailplane too. Unfortunatly, the small changes did not come across that well. When it did report good lift, I could "see" it was in good lift - kind of redundent. This was made 8 years ago and if re-made today, it would be much better. Good luck with the project and keep us informed on how it's going.

Gary
-

[MX]

Has anyone tried making an altimeter. I see Motorola have a suitable sensor, but it seems there must be a number of issues to get round, like non linear changes with height, calibration and then changes occuring due to turbulence etc.

I know there are one or two commercial systems out there - has anybody tried one ?

I tried making one. So far it's working pretty well: ZLog (http://www.hexpertsystems.com/zlog) :)

MX

[MX]

I was looking for something that might give me some information about when my glider encounters true lift - i find it hard to see this accurately from the ground, partly through inexperience and partly cos often its too far away to see subtle changes.

I was thinking if i had an alitimter (calibration not necessary as i'm not really interested in figures) then I could down link either an audio tone or data and use the info to improve my flight times.

I've got a video overlay setup in beta test right now. The altimeter outputs serial data through a simple interface to a 3rd party video overlay board. The video goes through a downlink to display on a monitor. This is being used for aerial photography, so they'll overlay the altitude on their camera's video output so they can get their shots at required altitudes.

I'm handy with Basic stamps so developing code and interfaces isn't an issue, but I'd be interested in how anyone else might have done this...

If you're doing your own telemetry link, my altimeter also outputs raw altitude data through its serial port that you could interface into your system. I'm about to test to see if I can interface my latest altimeter version (3.3v) directly with a BS2 (5v) (someone else has requested this too). Based on the PIC datasheet, it should work.

MX

[FFMan]

MX - are you saying the ZLOG can output the data in real time for you to collect via pic/stamp and transmit ?

Which video overlay board are you using. I looked at a few for overlaying rpm and pedal position information in my race car (boys and their toys eh ?) but never got as far as making it. In the end I put led displays on the dash and as these were visible in the picture anyhow, no overlay was required.

[MX]

MX - are you saying the ZLOG can output the data in real time for you to collect via pic/stamp and transmit ?

That's right.

Which video overlay board are you using. I looked at a few for overlaying rpm and pedal position information in my race car (boys and their toys eh ?) but never got as far as making it. In the end I put led displays on the dash and as these were visible in the picture anyhow, no overlay was required.

The overlay board is an OSD-232 from Intuitive Circuits (www.icircuits.com). Turned out to be easy to program.

MX

[Gary Warner]

That's right.



The overlay board is an OSD-232 from Intuitive Circuits (www.icircuits.com). Turned out to be easy to program.

MX

Corrected link: www.icircuits.com

[MX]

Corrected link: www.icircuits.com

Sorry about that. When you post a url in parenthesis, there is a bug in the forum software that sticks the second parenthesis inside the url tags.

MX

[Mr DIY]

Hi

I built an altimeter for use in thermal aircraft about 4 or more years ago. It has a real time downlink to a base station that displayed altitude in steps of 1 foot. It worked a treat .. the only problem being running out of range at times when reaching heights of 500 meters or higher. The highest recorded height has been around 800 meters (yes a 4 meter plane is quite small when that height). I am currently building 900MHz and a 2.4GHz downlink modules to try an improve reception. You tend to get drop outs as a plane does thermal turns, which is pretty much about antenna positions, antenna lengths and of course power. You need at least 19dbm transmit power to get any decent range. My latest receiver module is slightly smaller than a cell phone and can sit in your shirt pocket emitting tones .. or displaying data on its screen.

The airborne unit also had data logging facility that could be do downloaded and analyzed later.

A few observations when playing with altimeters.

High resolution (less than 1 foot) is not necessary
I would say that at about 0.5 meter resolution is about right.

Atmospheric pressure can change quite a bit over half an hour. (depending on weather) If you need higher accuracy, the base station ought to have a pressure sensor as well so that you can track and allow for pressure changes.

When in a thermal, the height gain can be quite significant. You can climb plenty meters per second very easily. You would be amazed how quickly a thermal plane can climb … and hence even a meter resolution can be more than adequate. For finding weak thermals, higher resolution helps find them more quickly.

Design issues.

Use a temperature compensated and signal conditioned sensors like the MPX range of sensors. They are more expensive than the standard sensors, but a lot easier to use.
To power the sensor, use a very stable voltage source. This is important. I power my sensor from a voltage reference. Some of the new accurate voltage regulators may work just as well though. To get the resolution required, you will need good low drift, temperature stable differential amplifier. You can make up such an amplifier using op amps in a quad package. You will need to find something with a good common mode specification though. I use Analog Devices amps in this application. The better the amplifiers used, the better the overall performance.

The micro used to sample the amplified pressure sensor voltage, can introduce switching noise that can result in having a noise level higher than the ADC resolution. You need to play around with lots of sampling and averaging to overcome this. Use a decent micro and pay attention to layout to minimize noise.


If you are interested, you can download a club magazine here, Jan/Feb 2005 issue ( Hmm .. I see that issue has a snip of Daryl Perkins visiting us :) )
http://www.southernsoaringclub.org.za/

and look at the graphs on page 12 and 14. The green is rate of climb and red shows sink.
These two graphs are just 2 of many printed in the magazine over the past few years.

Have fun
Brian

[Mr.RC-CAM]

Are there any convenient bench test methods for validating the accuracy of a new barometric design? Driving up to the mountains is really not all that efficient, at least not for me. I have seen some setups that used a DiY column of elevated water as barometric reference. In absence of a deep pockets lab environment, is that the extent of my options?

[FFMan]

On a slightly different front, does anyone know a video board that can create real time picture in picture from 2 composite feeds, and is small.

I race a historic formula ford and have for a while now been shooting video using a bullet camera mounted on my helmet, and this is great, useful for post mortem, good revision when you're about to go back to a circuit and fun. However i'd really like to run a second camera pointing backwards and display this in the top of the screen like a rear view mirror. Ideally this would be mixed in real time in the car, i think recording a second stream and editing later will a) mean i got to carry another recording device, and b) will be a headache to edit in later and get the time bases synced or the inserted video synced properly. it could be done but its a pain, the rear image doesn't have to be big, just let you see if someone if hassling you from behind.

I've found cctv systems around in 19inch racks - not ideal for the car !

anyone know of anything - got any ideas ?

[Mr DIY]

Are there any convenient bench test methods for validating the accuracy of a new barometric design? Driving up to the mountains is really not all that efficient, at least not for me. I have seen some setups that used a DiY column of elevated water as barometric reference. In absence of a deep pockets lab environment, is that the extent of my options?

I think so. It is the way I did it as explained here

http://www.repairfaq.org/filipg/RC/F_Altim.html

Brian

[Miami Mike]

On a slightly different front, does anyone know a video board...Welcome to RCGroups.com! This is a very interesting thread that you started, but to find answers to that question you really need to start another thread about that subject, not try to change the subject of this one in mid-stream.

Are there any convenient bench test methods for validating the accuracy of a new barometric design?For a variometer, just set it on your table and open your front door. You should get an indication that you're going down. Close the door and you'll get an indication that you're going up.

That's how my variometer reacts. I know it won't validate accuracy, but at least it would be a start.



.

[Mr.RC-CAM]

For a variometer, just set it on your table and open your front door. You should get an indication that you're going down. Close the door and you'll get an indication that you're going up.Yes, I had noticed that. The HVAC also causes the sensor to show changes in altitude. Both of these issues are sources of headaches too when they happen during testing. However, I am looking for ways to allow convenient altimeter design validation. I would like to conveniently simulate known altitudes, with decent accuracy, rather than relative changes. My budget is modest, so it will need to be DiY. The column of water trick is about all I have at this point. Sure would be nice to hear about other ways to do this.

[Acetronics]

Hi, Mr Cam

I've been interested in model altimeters for years ... the only two serious calibrating ways I know are:

1) THE Water column ... could also try alcohol for higher column !!!
2) if you can approach it ... maintenance calibration material for real aircrafts ( good friend needed ...)

What you describe for door openings is frequently used as Alarm detector !!!

Only software filtering will cancel such quick changes ...( have to recognise the type of change : slowly varying seems real, non linear is false ... ).

a :D note : for years, pilot's eyes have been the best detectors ....

Alain

[Gary Warner]

Are there any convenient bench test methods for validating the accuracy of a new barometric design? Driving up to the mountains is really not all that efficient, at least not for me. I have seen some setups that used a DiY column of elevated water as barometric reference. In absence of a deep pockets lab environment, is that the extent of my options?

I used a 'cheap' method of placing a altitude whrist-watch and the sensor in a jar and a vacumn was adjusted and calibration data taken. Worked very well.

Gary
--

[Mr.RC-CAM]

Thanks for the ideas. The altimeter watch method has the convenience I was looking for (hopefully they have accuracy that is trustworthy). For the vacuum jar, I was thinking of using the hand pump model from Edmund Scientific.

[Acetronics]

;)
Hi, Mr Cam

The problem is always the same : have an absolute reference; those hand pumps gauges have a really poor precision : say , at best 1 or 2 % of FS ...
so, it's not sufficient for an precise altimeter.

see i.e. http://www.mityvac.com/pages/products_hvpo.asp for hand pumps.

You can find convenient electronic gauges ( ~ 100 $ ...) here i.e. :
http://www.greisinger.de/index.php?sub=2.

;) Back to the main subject ... we were talking about variometer !!! so, if the rate of climb is not to be precisely mesured ...
There's no need for precise calibration !!! :D

Alain

[ALtitudeap]

MX here is a great OSD that you might be able to use. http://www.parallax.com/detail.asp?product_id=30015

[MX]

MX here is a great OSD that you might be able to use. http://www.parallax.com/detail.asp?product_id=30015

That looks interesting. I'll have to get one and see if ZLog will work with it. I've already got ZLog working with this one:

http://www.icircuits.com/prod_osd232.html

Thanks for the link,

MX

[FFMan]

MX That OSD looks neat. I was wondering whether on a simpler front you could program zlog to output a tone dependant on whether the model is rising or falling. This tone could then be transmitted to the ground using a simple audio link.

Could this be programmed as an option on a spare pin ? I'm not sure which pic your using and whether this is possible, otherwise i was thinking i could use the data feed from zlog, into a stamp and generate the tone from there but its one more device in the chain which one should always aim to keep as simple as possible.

thanks

[MX]

MX That OSD looks neat. I was wondering whether on a simpler front you could program zlog to output a tone dependant on whether the model is rising or falling. This tone could then be transmitted to the ground using a simple audio link.

Could this be programmed as an option on a spare pin ? I'm not sure which pic your using and whether this is possible, otherwise i was thinking i could use the data feed from zlog, into a stamp and generate the tone from there but its one more device in the chain which one should always aim to keep as simple as possible.

thanks

Might be possible. On MOD3, I brought out a couple I/O pins to pads on the bottom for expansion. I'll have to look at my timer to see what I could set up. How does a typical variometer function? Does the tone vary with rise/fall rate or does it just have a high tone for rising, a low tone for falling, and no tone for level?

[FFMan]

i'm not sure how exactly this works. Someone on this forum may know. I was thinking you could use a low beep for losing height and a high beep for climb. you could then vary the interval between the beeps depending on the rate of climb/descent. Ideally the noise should be of a type and level that isn't going to drive you nuts. Crusing at a fixed altitude should yield no sound, rising would give high beeps etc etc

If no one knows for sure, i can always go ask at one of the local gliding clubs.

[HLGNut]

Take a look at:

http://ludens.cl/Electron/Vario/vario.html

- Bob -

[willfly]

I made a variometer (rate of rise instrument) using Freescale Semiconductors MPX sensor. For telemetry it uses 900Mhz module - WiM900X (http://www.radiotronix.com/products/proddb.asp?ProdID=5)
Works for my 1.2 m sailplane. Radiotronix has new modules with 250mW Tx power which should suffice most sailplanes.

Calibration was easy. Just hop on a sailplane and use my Brauniger variometer as a reference. I used PIC 16F88 internal 10 bit ADC so vario resolution was poor. Might redo this with an external 14/16 bit ADC.

[willfly]

How does a typical variometer function? Does the tone vary with rise/fall rate or does it just have a high tone for rising, a low tone for falling, and no tone for level?

I use a Brauniger CompGPS variometer in hanggiding. Typically the beeps go up in pitch and rate with the rate of rise in thermal. for eg.
At 400 fpm it is beep.....beep.....beep
At 600 fpm it might be something like bep..bep..bep

There is no indication for normal decend, however a sink alarm can be turned on which is a continuoes tone of a very low pitch, something like poo...oon

[Jim_Marconnet]

I know this is an old thread.

I started a thread in sailplanes, thermal looking for a simple inexpensive variometer: http://www.rcgroups.com/forums/showthread.php?t=657998

It was pointed out to me that this DIY forum might be a better place to ask. So can anyone help me out with a simple, inexpensive variometer design or unit?

Thanks,
Jim Marconnet