sain

The upgraded microcontroller (a PIC16f887) sample has arrived, and I've decided to use it for the project instead of the PIC16f877a I've been testing with currently. The new controller is largely backwards compatible with the older one, but includes a handy internal oscillator (meaning the crystal and associated capacitor arn't needed). Anyway, hopefully it'll work fine with minimal changes. I was able to get the current display code working without any trouble, and I'll be testing the diode temp sensor tonight. I've been thinking more about the design for the thermocouple to pic interface. I think i'm just going to go with a quad op amp, with each op-amp output driving a different A/D channel on the pic - it has plenty to spare, so why not - this will be about the cheapest way to do it I think (assuming it works). It'll also make expanding to an 8 channel version very simple (just add another op-amp). At this stage I've also been thinking about what features to add to the system, besides just displaying the CHT temp. I would also welcome thoughts from others on what would be considered must-haves, should-haves, and would-be-nice-to-have. Should and would be nice options will be considered, and added if they don't increase the cost/difficulty of the unit to far. Must haves will be done if its achievable. This is what I have so far: Must Haves: Visual Alert approaching over temp. - i.e channel flashes until cleared. (mostly done) Visual Alert on over temp. - i.e channel double flashes until cleared. (mostly done) Variable display brightness (already done). Should Have: Audible alert on approaching over temp and over temp (i.e intermittent beeps until cleared) Would be Nice to have: Voice alert on approaching over temp and over temp (i.e speaks until cleared "CHT warning" or "CHT Alert") Data logging facility to SD Card or MMC card. Visual + audible alert on power supply problems (i.e warning when supplied power begins to drop - indicates charging/alternator fail) Option for user-definable colour settings for LEDs - for colour blind support. Suggestions welcome - even on prioritisation.

Just beware the dreaded "why is the sky blue?" question as they get a little bit older.. can result in quite an interesting discusion on wavelengths and harmonics though.

Last night's testing turned into an absolute shocker. The initial test using a post conversion offset worked fine, but the subsequent power off and back on testings (checking that the calibration remained valid after power off) didn't work as expected. I then reverted to the pre-conversion offset for calibration method and changed the code to store and load the calibrated value. This somehow resulted in the calibrated value being changed continually (lots of pretty lights on the display in other words). Unfortunately when I pulled the PIC and stuck it back in the programmer I broke the programmer, which took me a good while to realise, and several code revisions. A couple of hours later I had it all working again, and stable code (without the store and save bit, or the calibration adjustment code). I then added my new and improved calibration code (without the store and save) and it all went horribly wrong again. At this point I gave up and went to bed. I'll give it another crack tonight.

schematic for the diode temp sensor Here is the schematic for the diode based temp sensor i'll hopefully be using to do the cold junction offset calcs. [ATTACH]5425.vB[/ATTACH]

Thanks Mathew - I sure appreciate your support. :-p

You could always make one of those massive air cannon things they use at the the pumpkin chunkin festival....

The diode thermometer worked suprisingly well (first attempt even), and once calibrated was accurate to approx +-2deg C, which I think will be "close enough" for the cold junction calcs, especially as the inaccuracy is consistant. For those who want to build a simple and really cheap digital thermometer (with reasonableish accuracy) the site I used to get the idea for is here http://www.micro-examples.com/public/microex-navig/doc/098-temperature-sensor the sensor itself is consists of a 4k7 resistor connected between +5v and a 1n4148 diode, with the cathode (striped) end of the diode being connected to GND. The junction between the resistor and the diode is then connected to one of the AN pins on a PIC microcontroller (schematic to follow) The code for the PIC was a partial cut and paste job from the site listed above (the sensor read and conversion to deg C portions), and was then just a case of displaying the result on my already built test display. I chose to display it as a binary number, which was a simple as outputting the number to the display port, and turning on one of the display channels. I also added code to log the first 16 reads to the PICs internal eeprom (to be read later by the computer). Testing was done by placing a k-type thermocouple (connected to my multimeter set to display deg C) next to the diode and then reading the temps on both. The initial test run (no calibration) had the diode sensor showing consistantly 5 deg lower. I'm planning on doing some further work on the calibration code tonight, with the calibration changing the results of the deg C conversion, rather than the initially read value - I believe this will make the calibration easier and quicker. If that works I'll then test storing the calibration value in the eeprom and loading this at startup. If that works I'll be good to move on to the thermocouple sensor portion..

Goulburn certainly gets pretty cold. I think I only had 2 sub-zero flying days (at ground level before take off) last year though, so it wasn't all thaaaaaaaaaat bad. The gazelle does have a cabin heater, but its pretty ineffective unfortunately. I think I might try and get hold of a set of heated moterbike gloves for her - good suggestion that - thanks muchly.

I don't think my chances of getting her into a trike are particularly good - given her reaction to an open cockpit thruster was "no chance". Sounds fun to me though.

fantastic call I think she probably wants kids one day...

As we start to get into the season of chillier weather I thought I'd ask what everybody does for their comfort? Over winter last year the Gazelle was quite frigid to fly around in, especially with my tendancy to airsickness requiring the window vents to be opened. I delt with this by just putting on a few extra layers and was quite comfortable, but I'm hoping this year to take my GF for a flight or two, and she feels the cold a lot more than I do.... Is it just a case of bundling her up in ski gear etc till she looks like the good year blimp and hoping the seat belt will still fit, or does anybody have any tips? I was thinking a set of those gel handwarmers that Katmandu sells might be the go, or perhaps a hot water bottle, warn between a couple of layers of clothing.

Sweet - thanks Ian!

Its normal to use thermocouple wire for the extensions - you can buy this in lengths or by the spool from various different places.

Not much progress due to me being a lazy **** recently. Last night I finally did some more work on it, wiring up the diode temperature sensor and writing the program to measure it. The diode will be used to provide a reference temperature which will be used to perform the cold junction offset compensation for the thermocouples. There are a couple of disadvantages to going this way, mainly that it makes the code more complicated than using a dedicated cold junction compensator chip, but it is a fair bit cheaper. Test of the diode temp sensor should be tonight - I got called away to dinner at my gf's parents before I could test it. I'm also awaiting delivery of a couple of samples - a new PIC microcontroller from microchip and a cold junction compensator chip from analog devices. Both should be arriving this week sometime hopefully. The new PIC is the recommended replacement for the 16f877a (which apparantly should no longer be used for new designs). Hopefully I'll be able to make the circuit and code compatible with both devices. The cold junction compensator will be used to confirm that the diode compensation stuff is working as intended, or if it fails dismally as part of the circuit itself. I've also been having a few issues with the op-amp amplifier circuit for the thermocouple (to bring the output up to something the PIC can read). I think the issue is just that the room temp voltage output is in the noise threshold for the op-amp i was using. I'll try a different one soon. Extra-bits to be used in the project: 1x 4k7 resistor, 1 x 1n4148 small signal diode: $0.70 Total so far: $33.51

Yeah, that was mine too... what I thought the origional quote I posed said was "you want to fly, you have to have one of these" Turns out I was wrong..

sorry for the double post :im with stupid:whups, clicked the application button and answered my own question: :sorry:all

Today my boss (knowing I'm aviation obsessed, and being a pilot himself) forwarded me the CASA breifing (http://casa.gov.au/corporat/casabriefing/08Mar.htm) to read, which had the very interesting line: All active pilots over 18 years must undergo a background security check and be issued with one of the identification cards. Does this apply to RA-AUS Pilot Certificate holders like me? I was under the impression that you only needed to get the background checks done if your flying into security controlled airports, but this seems to be saying that we still need to get them done if we want to fly at all (and recieve our value-for-money-i-just-burned-$181 AVID card). Can anybody clarify that for me? Personally I'd much rather spend that money going flying than on a chunk of plastic with my photo on it.

Good choice in the end I think Geoff. You can still use the power supply to run some other device - you can set the voltage output on the LM338 to whatever you want (as long as its approx 2.5volts below the supply)... I was initially horrified at how much he was charging you for the power supply until I stopped to think about it and came up with 2hrs labour + parts + gst coming out at remarkably close to the $250. And I think it'd take me longer than 2hrs to build it (including making pcb etc).

Great news, fantastic job volksy - you and your dad should be very proud of what you've achieved - not just for the club, but the entire goulburn community.

Short answer is yes he is right (I think), but wont the radio switch to its own battery pack when the external supply is removed (i.e giving you some more talk time)? Easiest way to tell would be to plug a power adaptor into the radio but don't hook it up to any power, and then seeing if you can still talk. Long answer: The dropout on the lm338 based mainly on the difference between the input and output voltages, and the amount of current being drawn by the load (radio). Ideally you want the input and output voltages difference to be about 2.5 - 3 volts (assuming a 3A load - you can get away with a bit lower for a smaller load) - which in normal conditions wont be a problem for this circuit. More than that and you have to problems with excess heat needing to be dissapated, and less than that and the regulator wont function. What its going to come down to is how much current your radio draws (i don't know i'm afraid). Datasheet for the lm338 is here if your interested http://www.national.com/ds.cgi/LM/LM138.pdf The circuit supplied by Zulu1 wont fix all your problems with noise etc, but will supply a good, clean source of power in normal circumstances, which gives the radio a better chance of working right. If the alternator fails, you should still have the radios battery, which is a much better situation than you'd be in with a fixed radio. I'd follow his suggestions for RF noise elimination on the mic lines as well - thats probably your other "big" source of noise. I'll see if I can get my hands on a spare headset to pull apart so I can do up a set of how-to instructions - unfortunately my free cash is going on other projects, so my hopes arn't high. Failing that you'll need to rely on Zulu1 (sorry Paul :-p)

Doesn't Great Plains sell alternators for VW engines? They seem to attach to the crankshaft, rather than to the spinner backing plate like you were saying. I'd be worried about unbalancing the prop if you were attaching magnets to the backing plate. Anyway, pretty pictures of one of the alternators being installed: http://bobhooversblog.blogspot.com/2007/06/av-reliable-ignition.html Great Plains site: http://www.greatplainsas.com/scindex.html

I did a fair bit of listening to music through my david clarks (forgotten which model) while I was building my mp3 mixer circuit (see the kit building section). The quality was suprisingly good, but they are only mono so... On the whole listening to music while flying thing - I find there is generally so much radio traffic happening that your not going to get a chance to listen to music anyways, and your favourite songs will keep getting muted for the radio. I came up with the idea for the mp3 mixer after a particularly quite afternoon session of circuits where I was the only one around, and hence the only interruptions would have been my own. That sort of day just doesn't seem to come up that often.

Our instructor took a bunch of us to visit ATC at sydney, which was a very useful experience for me. One of the things they stressed was if you think your in trouble, don't hesitate to ask for help - Its much easier for them if they get in on the situation early. They also gave us a couple of example cases of what not to do, such as the gentleman who called for help because he was lost, and all he could tell them was "I'm over water". The water turned out to be the parramatta river, with land and houses each side (he was up the narrow end). It was also quite scary watching some of the near miss tracks on people infringing airspace... One guy had a very close encounter with a RAAF herc. Anyway, if you think you need help ask for it, thats one of the things they are there for.

I'm fairly new to the nav stuff (only recently passed my test) but I found it helped a lot to have a plan for when your going to do stuff, so you don't forget things (like writing down ATD... whups). This can be as simple as thinking the whole flight through in your head, maybe with reminders written on your map for when you need to do certain things, like frequency changes and inbound calls. Think about the major landmarks you'll be looking for as well, so you can easily keep track of where you are on the flight. The other thing I found I needed to do was practice doing the paper plans a lot, and do "imaginary flights" where I do the time/speed checks on the whizzy wheel. I found without a fair bit of practice that I was very slow doing the revised estimates, despite this being quite an easy one to do. If your amazingly bad at maths (like i am) it might be wise to blue tac a el cheapo calculator to your kneeboard/folder, so you can quickly check your mental arithmatic. Another thing that is good to practice is to write down 6 or so towns (or nearby airfields) and then use a dice to pick one. Plan a divert to that town from some random point on your plan (though make it easy for yourself and make sure the point is right next to/over an easily recognisable landmark). Remeber the instructor is going to do this to you in flight, so its handy to be able to do it quickly and easily. If your instructor is nice they might hold the stick for you while your doing this, but you might want to practice doing the wizzy wheel calcs one handed (just in case they are busy picking up starbursts...). With regard to landmarks make sure you check with some of the more experienced pilots that they are actually there... don't do what I did on my first nav and pick the midpoint on a dried up lake as a point for my timecheck, or on my first solo nav when I picked a town that doesn't exist yet as a waypoint where I needed to change direction. Which reminds me... practice doing your diverts - it really sucks trying to do one while your brain is going "oh crap, i'm lost - should I call melbourne centre and ask for a heading to my next waypoint (or home!), or trust that those landmarks down there are the ones i think they are on my map" and turbulance is bouncing the plane around. Hope that doesn't sound scary (because its only momentarily scary). Basically just practice lots, think about what things on your map are going to look like and don't be afraid to call for help if you end up not being able to figure out where you are - it'll take hardly any time for the controller to figure out where you are, and give you a heading to fly to get you somewhere safe. My first solo nav was a wonderful experience (flew past bungonia gorge - very pretty from the air), despite getting myself lost (and finding myself) twice. Its a great feeling cruising along a few thousand feet up, watching the scenary go by (landmarks - yay I'm not lost!), following a plan that i'd made myself (well, diversions on a plan i made myself (damn, i'm lost!)) and listening to the friendly chatter on the radio. Anyway, enjoy the your next nav - hope my advice helps you avoid the mistakes I made. EDIT: Re: your invention Ian sells them at clearprop in the nav section - the little nav computer dohickey. Laptop software wise this would also be very easy to do, but the whizzy wheel does get very quick and easy with practice, and its a lot cheaper.

Personally those things make me nervous. How do you control them once they are deployed? what happens when you arrive at the ground and the wind is still blowing? will the plane get dragged, or is there a quick release mechanism? There was a site I found when I was first researching stuff about flying and it cited an example in the US where a plane in trouble had deployed their chute, decended to the ground safely and then been flipped and dragged along the ground for a couple of miles killing the occupants. I think in certain situations they could be life savers, but a lot of thought needs to be given by the operators as to when they are best used. If treated as the option of last resort, not the first thing you pull when the engine cuts out, I think they are a wonderful idea.